forked from Minki/linux
f12e4ed8f0
Update the documentation for crypto_register_algs() and crypto_unregister_algs() to match the actual behavior. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2093 lines
69 KiB
XML
2093 lines
69 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
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<book id="KernelCryptoAPI">
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<bookinfo>
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<title>Linux Kernel Crypto API</title>
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<authorgroup>
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<author>
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<firstname>Stephan</firstname>
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<surname>Mueller</surname>
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<affiliation>
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<address>
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<email>smueller@chronox.de</email>
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</address>
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</affiliation>
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</author>
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<author>
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<firstname>Marek</firstname>
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<surname>Vasut</surname>
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<affiliation>
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<address>
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<email>marek@denx.de</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<copyright>
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<year>2014</year>
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<holder>Stephan Mueller</holder>
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</copyright>
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<legalnotice>
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<para>
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This documentation is free software; you can redistribute
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it and/or modify it under the terms of the GNU General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later
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version.
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</para>
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<para>
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This program is distributed in the hope that it will be
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useful, but WITHOUT ANY WARRANTY; without even the implied
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warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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See the GNU General Public License for more details.
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</para>
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<para>
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You should have received a copy of the GNU General Public
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License along with this program; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
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MA 02111-1307 USA
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</para>
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<para>
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For more details see the file COPYING in the source
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distribution of Linux.
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</para>
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</legalnotice>
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</bookinfo>
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<toc></toc>
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<chapter id="Intro">
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<title>Kernel Crypto API Interface Specification</title>
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<sect1><title>Introduction</title>
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<para>
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The kernel crypto API offers a rich set of cryptographic ciphers as
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well as other data transformation mechanisms and methods to invoke
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these. This document contains a description of the API and provides
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example code.
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</para>
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<para>
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To understand and properly use the kernel crypto API a brief
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explanation of its structure is given. Based on the architecture,
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the API can be separated into different components. Following the
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architecture specification, hints to developers of ciphers are
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provided. Pointers to the API function call documentation are
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given at the end.
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</para>
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<para>
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The kernel crypto API refers to all algorithms as "transformations".
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Therefore, a cipher handle variable usually has the name "tfm".
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Besides cryptographic operations, the kernel crypto API also knows
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compression transformations and handles them the same way as ciphers.
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</para>
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<para>
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The kernel crypto API serves the following entity types:
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<itemizedlist>
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<listitem>
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<para>consumers requesting cryptographic services</para>
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</listitem>
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<listitem>
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<para>data transformation implementations (typically ciphers)
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that can be called by consumers using the kernel crypto
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API</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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This specification is intended for consumers of the kernel crypto
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API as well as for developers implementing ciphers. This API
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specification, however, does not discuss all API calls available
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to data transformation implementations (i.e. implementations of
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ciphers and other transformations (such as CRC or even compression
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algorithms) that can register with the kernel crypto API).
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</para>
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<para>
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Note: The terms "transformation" and cipher algorithm are used
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interchangeably.
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</para>
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</sect1>
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<sect1><title>Terminology</title>
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<para>
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The transformation implementation is an actual code or interface
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to hardware which implements a certain transformation with precisely
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defined behavior.
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</para>
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<para>
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The transformation object (TFM) is an instance of a transformation
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implementation. There can be multiple transformation objects
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associated with a single transformation implementation. Each of
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those transformation objects is held by a crypto API consumer or
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another transformation. Transformation object is allocated when a
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crypto API consumer requests a transformation implementation.
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The consumer is then provided with a structure, which contains
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a transformation object (TFM).
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</para>
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<para>
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The structure that contains transformation objects may also be
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referred to as a "cipher handle". Such a cipher handle is always
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subject to the following phases that are reflected in the API calls
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applicable to such a cipher handle:
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</para>
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<orderedlist>
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<listitem>
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<para>Initialization of a cipher handle.</para>
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</listitem>
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<listitem>
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<para>Execution of all intended cipher operations applicable
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for the handle where the cipher handle must be furnished to
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every API call.</para>
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</listitem>
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<listitem>
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<para>Destruction of a cipher handle.</para>
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</listitem>
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</orderedlist>
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<para>
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When using the initialization API calls, a cipher handle is
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created and returned to the consumer. Therefore, please refer
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to all initialization API calls that refer to the data
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structure type a consumer is expected to receive and subsequently
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to use. The initialization API calls have all the same naming
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conventions of crypto_alloc_*.
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</para>
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<para>
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The transformation context is private data associated with
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the transformation object.
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</para>
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</sect1>
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</chapter>
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<chapter id="Architecture"><title>Kernel Crypto API Architecture</title>
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<sect1><title>Cipher algorithm types</title>
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<para>
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The kernel crypto API provides different API calls for the
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following cipher types:
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<itemizedlist>
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<listitem><para>Symmetric ciphers</para></listitem>
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<listitem><para>AEAD ciphers</para></listitem>
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<listitem><para>Message digest, including keyed message digest</para></listitem>
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<listitem><para>Random number generation</para></listitem>
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<listitem><para>User space interface</para></listitem>
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</itemizedlist>
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</para>
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</sect1>
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<sect1><title>Ciphers And Templates</title>
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<para>
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The kernel crypto API provides implementations of single block
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ciphers and message digests. In addition, the kernel crypto API
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provides numerous "templates" that can be used in conjunction
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with the single block ciphers and message digests. Templates
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include all types of block chaining mode, the HMAC mechanism, etc.
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</para>
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<para>
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Single block ciphers and message digests can either be directly
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used by a caller or invoked together with a template to form
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multi-block ciphers or keyed message digests.
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</para>
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<para>
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A single block cipher may even be called with multiple templates.
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However, templates cannot be used without a single cipher.
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</para>
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<para>
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See /proc/crypto and search for "name". For example:
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<itemizedlist>
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<listitem><para>aes</para></listitem>
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<listitem><para>ecb(aes)</para></listitem>
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<listitem><para>cmac(aes)</para></listitem>
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<listitem><para>ccm(aes)</para></listitem>
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<listitem><para>rfc4106(gcm(aes))</para></listitem>
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<listitem><para>sha1</para></listitem>
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<listitem><para>hmac(sha1)</para></listitem>
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<listitem><para>authenc(hmac(sha1),cbc(aes))</para></listitem>
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</itemizedlist>
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</para>
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<para>
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In these examples, "aes" and "sha1" are the ciphers and all
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others are the templates.
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</para>
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</sect1>
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<sect1><title>Synchronous And Asynchronous Operation</title>
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<para>
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The kernel crypto API provides synchronous and asynchronous
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API operations.
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</para>
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<para>
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When using the synchronous API operation, the caller invokes
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a cipher operation which is performed synchronously by the
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kernel crypto API. That means, the caller waits until the
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cipher operation completes. Therefore, the kernel crypto API
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calls work like regular function calls. For synchronous
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operation, the set of API calls is small and conceptually
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similar to any other crypto library.
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</para>
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<para>
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Asynchronous operation is provided by the kernel crypto API
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which implies that the invocation of a cipher operation will
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complete almost instantly. That invocation triggers the
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cipher operation but it does not signal its completion. Before
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invoking a cipher operation, the caller must provide a callback
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function the kernel crypto API can invoke to signal the
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completion of the cipher operation. Furthermore, the caller
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must ensure it can handle such asynchronous events by applying
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appropriate locking around its data. The kernel crypto API
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does not perform any special serialization operation to protect
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the caller's data integrity.
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</para>
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</sect1>
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<sect1><title>Crypto API Cipher References And Priority</title>
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<para>
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A cipher is referenced by the caller with a string. That string
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has the following semantics:
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<programlisting>
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template(single block cipher)
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</programlisting>
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where "template" and "single block cipher" is the aforementioned
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template and single block cipher, respectively. If applicable,
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additional templates may enclose other templates, such as
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<programlisting>
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template1(template2(single block cipher)))
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</programlisting>
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</para>
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<para>
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The kernel crypto API may provide multiple implementations of a
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template or a single block cipher. For example, AES on newer
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Intel hardware has the following implementations: AES-NI,
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assembler implementation, or straight C. Now, when using the
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string "aes" with the kernel crypto API, which cipher
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implementation is used? The answer to that question is the
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priority number assigned to each cipher implementation by the
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kernel crypto API. When a caller uses the string to refer to a
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cipher during initialization of a cipher handle, the kernel
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crypto API looks up all implementations providing an
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implementation with that name and selects the implementation
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with the highest priority.
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</para>
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<para>
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Now, a caller may have the need to refer to a specific cipher
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implementation and thus does not want to rely on the
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priority-based selection. To accommodate this scenario, the
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kernel crypto API allows the cipher implementation to register
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a unique name in addition to common names. When using that
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unique name, a caller is therefore always sure to refer to
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the intended cipher implementation.
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</para>
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<para>
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The list of available ciphers is given in /proc/crypto. However,
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that list does not specify all possible permutations of
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templates and ciphers. Each block listed in /proc/crypto may
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contain the following information -- if one of the components
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listed as follows are not applicable to a cipher, it is not
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displayed:
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</para>
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<itemizedlist>
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<listitem>
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<para>name: the generic name of the cipher that is subject
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to the priority-based selection -- this name can be used by
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the cipher allocation API calls (all names listed above are
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examples for such generic names)</para>
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</listitem>
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<listitem>
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<para>driver: the unique name of the cipher -- this name can
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be used by the cipher allocation API calls</para>
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</listitem>
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<listitem>
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<para>module: the kernel module providing the cipher
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implementation (or "kernel" for statically linked ciphers)</para>
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</listitem>
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<listitem>
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<para>priority: the priority value of the cipher implementation</para>
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</listitem>
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<listitem>
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<para>refcnt: the reference count of the respective cipher
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(i.e. the number of current consumers of this cipher)</para>
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</listitem>
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<listitem>
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<para>selftest: specification whether the self test for the
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cipher passed</para>
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</listitem>
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<listitem>
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<para>type:
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<itemizedlist>
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<listitem>
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<para>skcipher for symmetric key ciphers</para>
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</listitem>
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<listitem>
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<para>cipher for single block ciphers that may be used with
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an additional template</para>
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</listitem>
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<listitem>
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<para>shash for synchronous message digest</para>
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</listitem>
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<listitem>
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<para>ahash for asynchronous message digest</para>
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</listitem>
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<listitem>
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<para>aead for AEAD cipher type</para>
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</listitem>
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<listitem>
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<para>compression for compression type transformations</para>
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</listitem>
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<listitem>
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<para>rng for random number generator</para>
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</listitem>
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<listitem>
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<para>givcipher for cipher with associated IV generator
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(see the geniv entry below for the specification of the
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IV generator type used by the cipher implementation)</para>
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</listitem>
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</itemizedlist>
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</para>
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</listitem>
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<listitem>
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<para>blocksize: blocksize of cipher in bytes</para>
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</listitem>
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<listitem>
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<para>keysize: key size in bytes</para>
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</listitem>
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<listitem>
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<para>ivsize: IV size in bytes</para>
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</listitem>
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<listitem>
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<para>seedsize: required size of seed data for random number
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generator</para>
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</listitem>
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<listitem>
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<para>digestsize: output size of the message digest</para>
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</listitem>
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<listitem>
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<para>geniv: IV generation type:
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<itemizedlist>
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<listitem>
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<para>eseqiv for encrypted sequence number based IV
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generation</para>
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</listitem>
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<listitem>
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<para>seqiv for sequence number based IV generation</para>
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</listitem>
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<listitem>
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<para>chainiv for chain iv generation</para>
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</listitem>
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<listitem>
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<para><builtin> is a marker that the cipher implements
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IV generation and handling as it is specific to the given
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cipher</para>
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</listitem>
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</itemizedlist>
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</para>
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</listitem>
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</itemizedlist>
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</sect1>
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<sect1><title>Key Sizes</title>
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<para>
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When allocating a cipher handle, the caller only specifies the
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cipher type. Symmetric ciphers, however, typically support
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multiple key sizes (e.g. AES-128 vs. AES-192 vs. AES-256).
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These key sizes are determined with the length of the provided
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key. Thus, the kernel crypto API does not provide a separate
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way to select the particular symmetric cipher key size.
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</para>
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</sect1>
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<sect1><title>Cipher Allocation Type And Masks</title>
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<para>
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The different cipher handle allocation functions allow the
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specification of a type and mask flag. Both parameters have
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the following meaning (and are therefore not covered in the
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subsequent sections).
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</para>
|
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|
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<para>
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The type flag specifies the type of the cipher algorithm.
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The caller usually provides a 0 when the caller wants the
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default handling. Otherwise, the caller may provide the
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following selections which match the aforementioned cipher
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types:
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</para>
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|
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<itemizedlist>
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<listitem>
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<para>CRYPTO_ALG_TYPE_CIPHER Single block cipher</para>
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</listitem>
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|
<listitem>
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<para>CRYPTO_ALG_TYPE_COMPRESS Compression</para>
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</listitem>
|
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<listitem>
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<para>CRYPTO_ALG_TYPE_AEAD Authenticated Encryption with
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Associated Data (MAC)</para>
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</listitem>
|
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<listitem>
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<para>CRYPTO_ALG_TYPE_BLKCIPHER Synchronous multi-block cipher</para>
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</listitem>
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<listitem>
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<para>CRYPTO_ALG_TYPE_ABLKCIPHER Asynchronous multi-block cipher</para>
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|
</listitem>
|
|
<listitem>
|
|
<para>CRYPTO_ALG_TYPE_GIVCIPHER Asynchronous multi-block
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cipher packed together with an IV generator (see geniv field
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|
in the /proc/crypto listing for the known IV generators)</para>
|
|
</listitem>
|
|
<listitem>
|
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<para>CRYPTO_ALG_TYPE_DIGEST Raw message digest</para>
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</listitem>
|
|
<listitem>
|
|
<para>CRYPTO_ALG_TYPE_HASH Alias for CRYPTO_ALG_TYPE_DIGEST</para>
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</listitem>
|
|
<listitem>
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<para>CRYPTO_ALG_TYPE_SHASH Synchronous multi-block hash</para>
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|
</listitem>
|
|
<listitem>
|
|
<para>CRYPTO_ALG_TYPE_AHASH Asynchronous multi-block hash</para>
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|
</listitem>
|
|
<listitem>
|
|
<para>CRYPTO_ALG_TYPE_RNG Random Number Generation</para>
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|
</listitem>
|
|
<listitem>
|
|
<para>CRYPTO_ALG_TYPE_AKCIPHER Asymmetric cipher</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>CRYPTO_ALG_TYPE_PCOMPRESS Enhanced version of
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CRYPTO_ALG_TYPE_COMPRESS allowing for segmented compression /
|
|
decompression instead of performing the operation on one
|
|
segment only. CRYPTO_ALG_TYPE_PCOMPRESS is intended to replace
|
|
CRYPTO_ALG_TYPE_COMPRESS once existing consumers are converted.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The mask flag restricts the type of cipher. The only allowed
|
|
flag is CRYPTO_ALG_ASYNC to restrict the cipher lookup function
|
|
to asynchronous ciphers. Usually, a caller provides a 0 for the
|
|
mask flag.
|
|
</para>
|
|
|
|
<para>
|
|
When the caller provides a mask and type specification, the
|
|
caller limits the search the kernel crypto API can perform for
|
|
a suitable cipher implementation for the given cipher name.
|
|
That means, even when a caller uses a cipher name that exists
|
|
during its initialization call, the kernel crypto API may not
|
|
select it due to the used type and mask field.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1><title>Internal Structure of Kernel Crypto API</title>
|
|
|
|
<para>
|
|
The kernel crypto API has an internal structure where a cipher
|
|
implementation may use many layers and indirections. This section
|
|
shall help to clarify how the kernel crypto API uses
|
|
various components to implement the complete cipher.
|
|
</para>
|
|
|
|
<para>
|
|
The following subsections explain the internal structure based
|
|
on existing cipher implementations. The first section addresses
|
|
the most complex scenario where all other scenarios form a logical
|
|
subset.
|
|
</para>
|
|
|
|
<sect2><title>Generic AEAD Cipher Structure</title>
|
|
|
|
<para>
|
|
The following ASCII art decomposes the kernel crypto API layers
|
|
when using the AEAD cipher with the automated IV generation. The
|
|
shown example is used by the IPSEC layer.
|
|
</para>
|
|
|
|
<para>
|
|
For other use cases of AEAD ciphers, the ASCII art applies as
|
|
well, but the caller may not use the AEAD cipher with a separate
|
|
IV generator. In this case, the caller must generate the IV.
|
|
</para>
|
|
|
|
<para>
|
|
The depicted example decomposes the AEAD cipher of GCM(AES) based
|
|
on the generic C implementations (gcm.c, aes-generic.c, ctr.c,
|
|
ghash-generic.c, seqiv.c). The generic implementation serves as an
|
|
example showing the complete logic of the kernel crypto API.
|
|
</para>
|
|
|
|
<para>
|
|
It is possible that some streamlined cipher implementations (like
|
|
AES-NI) provide implementations merging aspects which in the view
|
|
of the kernel crypto API cannot be decomposed into layers any more.
|
|
In case of the AES-NI implementation, the CTR mode, the GHASH
|
|
implementation and the AES cipher are all merged into one cipher
|
|
implementation registered with the kernel crypto API. In this case,
|
|
the concept described by the following ASCII art applies too. However,
|
|
the decomposition of GCM into the individual sub-components
|
|
by the kernel crypto API is not done any more.
|
|
</para>
|
|
|
|
<para>
|
|
Each block in the following ASCII art is an independent cipher
|
|
instance obtained from the kernel crypto API. Each block
|
|
is accessed by the caller or by other blocks using the API functions
|
|
defined by the kernel crypto API for the cipher implementation type.
|
|
</para>
|
|
|
|
<para>
|
|
The blocks below indicate the cipher type as well as the specific
|
|
logic implemented in the cipher.
|
|
</para>
|
|
|
|
<para>
|
|
The ASCII art picture also indicates the call structure, i.e. who
|
|
calls which component. The arrows point to the invoked block
|
|
where the caller uses the API applicable to the cipher type
|
|
specified for the block.
|
|
</para>
|
|
|
|
<programlisting>
|
|
<![CDATA[
|
|
kernel crypto API | IPSEC Layer
|
|
|
|
|
+-----------+ |
|
|
| | (1)
|
|
| aead | <----------------------------------- esp_output
|
|
| (seqiv) | ---+
|
|
+-----------+ |
|
|
| (2)
|
|
+-----------+ |
|
|
| | <--+ (2)
|
|
| aead | <----------------------------------- esp_input
|
|
| (gcm) | ------------+
|
|
+-----------+ |
|
|
| (3) | (5)
|
|
v v
|
|
+-----------+ +-----------+
|
|
| | | |
|
|
| skcipher | | ahash |
|
|
| (ctr) | ---+ | (ghash) |
|
|
+-----------+ | +-----------+
|
|
|
|
|
+-----------+ | (4)
|
|
| | <--+
|
|
| cipher |
|
|
| (aes) |
|
|
+-----------+
|
|
]]>
|
|
</programlisting>
|
|
|
|
<para>
|
|
The following call sequence is applicable when the IPSEC layer
|
|
triggers an encryption operation with the esp_output function. During
|
|
configuration, the administrator set up the use of rfc4106(gcm(aes)) as
|
|
the cipher for ESP. The following call sequence is now depicted in the
|
|
ASCII art above:
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
esp_output() invokes crypto_aead_encrypt() to trigger an encryption
|
|
operation of the AEAD cipher with IV generator.
|
|
</para>
|
|
|
|
<para>
|
|
In case of GCM, the SEQIV implementation is registered as GIVCIPHER
|
|
in crypto_rfc4106_alloc().
|
|
</para>
|
|
|
|
<para>
|
|
The SEQIV performs its operation to generate an IV where the core
|
|
function is seqiv_geniv().
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Now, SEQIV uses the AEAD API function calls to invoke the associated
|
|
AEAD cipher. In our case, during the instantiation of SEQIV, the
|
|
cipher handle for GCM is provided to SEQIV. This means that SEQIV
|
|
invokes AEAD cipher operations with the GCM cipher handle.
|
|
</para>
|
|
|
|
<para>
|
|
During instantiation of the GCM handle, the CTR(AES) and GHASH
|
|
ciphers are instantiated. The cipher handles for CTR(AES) and GHASH
|
|
are retained for later use.
|
|
</para>
|
|
|
|
<para>
|
|
The GCM implementation is responsible to invoke the CTR mode AES and
|
|
the GHASH cipher in the right manner to implement the GCM
|
|
specification.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The GCM AEAD cipher type implementation now invokes the SKCIPHER API
|
|
with the instantiated CTR(AES) cipher handle.
|
|
</para>
|
|
|
|
<para>
|
|
During instantiation of the CTR(AES) cipher, the CIPHER type
|
|
implementation of AES is instantiated. The cipher handle for AES is
|
|
retained.
|
|
</para>
|
|
|
|
<para>
|
|
That means that the SKCIPHER implementation of CTR(AES) only
|
|
implements the CTR block chaining mode. After performing the block
|
|
chaining operation, the CIPHER implementation of AES is invoked.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The SKCIPHER of CTR(AES) now invokes the CIPHER API with the AES
|
|
cipher handle to encrypt one block.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The GCM AEAD implementation also invokes the GHASH cipher
|
|
implementation via the AHASH API.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
When the IPSEC layer triggers the esp_input() function, the same call
|
|
sequence is followed with the only difference that the operation starts
|
|
with step (2).
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2><title>Generic Block Cipher Structure</title>
|
|
<para>
|
|
Generic block ciphers follow the same concept as depicted with the ASCII
|
|
art picture above.
|
|
</para>
|
|
|
|
<para>
|
|
For example, CBC(AES) is implemented with cbc.c, and aes-generic.c. The
|
|
ASCII art picture above applies as well with the difference that only
|
|
step (4) is used and the SKCIPHER block chaining mode is CBC.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2><title>Generic Keyed Message Digest Structure</title>
|
|
<para>
|
|
Keyed message digest implementations again follow the same concept as
|
|
depicted in the ASCII art picture above.
|
|
</para>
|
|
|
|
<para>
|
|
For example, HMAC(SHA256) is implemented with hmac.c and
|
|
sha256_generic.c. The following ASCII art illustrates the
|
|
implementation:
|
|
</para>
|
|
|
|
<programlisting>
|
|
<![CDATA[
|
|
kernel crypto API | Caller
|
|
|
|
|
+-----------+ (1) |
|
|
| | <------------------ some_function
|
|
| ahash |
|
|
| (hmac) | ---+
|
|
+-----------+ |
|
|
| (2)
|
|
+-----------+ |
|
|
| | <--+
|
|
| shash |
|
|
| (sha256) |
|
|
+-----------+
|
|
]]>
|
|
</programlisting>
|
|
|
|
<para>
|
|
The following call sequence is applicable when a caller triggers
|
|
an HMAC operation:
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
The AHASH API functions are invoked by the caller. The HMAC
|
|
implementation performs its operation as needed.
|
|
</para>
|
|
|
|
<para>
|
|
During initialization of the HMAC cipher, the SHASH cipher type of
|
|
SHA256 is instantiated. The cipher handle for the SHA256 instance is
|
|
retained.
|
|
</para>
|
|
|
|
<para>
|
|
At one time, the HMAC implementation requires a SHA256 operation
|
|
where the SHA256 cipher handle is used.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The HMAC instance now invokes the SHASH API with the SHA256
|
|
cipher handle to calculate the message digest.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</sect2>
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<chapter id="Development"><title>Developing Cipher Algorithms</title>
|
|
<sect1><title>Registering And Unregistering Transformation</title>
|
|
<para>
|
|
There are three distinct types of registration functions in
|
|
the Crypto API. One is used to register a generic cryptographic
|
|
transformation, while the other two are specific to HASH
|
|
transformations and COMPRESSion. We will discuss the latter
|
|
two in a separate chapter, here we will only look at the
|
|
generic ones.
|
|
</para>
|
|
|
|
<para>
|
|
Before discussing the register functions, the data structure
|
|
to be filled with each, struct crypto_alg, must be considered
|
|
-- see below for a description of this data structure.
|
|
</para>
|
|
|
|
<para>
|
|
The generic registration functions can be found in
|
|
include/linux/crypto.h and their definition can be seen below.
|
|
The former function registers a single transformation, while
|
|
the latter works on an array of transformation descriptions.
|
|
The latter is useful when registering transformations in bulk,
|
|
for example when a driver implements multiple transformations.
|
|
</para>
|
|
|
|
<programlisting>
|
|
int crypto_register_alg(struct crypto_alg *alg);
|
|
int crypto_register_algs(struct crypto_alg *algs, int count);
|
|
</programlisting>
|
|
|
|
<para>
|
|
The counterparts to those functions are listed below.
|
|
</para>
|
|
|
|
<programlisting>
|
|
int crypto_unregister_alg(struct crypto_alg *alg);
|
|
int crypto_unregister_algs(struct crypto_alg *algs, int count);
|
|
</programlisting>
|
|
|
|
<para>
|
|
Notice that both registration and unregistration functions
|
|
do return a value, so make sure to handle errors. A return
|
|
code of zero implies success. Any return code < 0 implies
|
|
an error.
|
|
</para>
|
|
|
|
<para>
|
|
The bulk registration/unregistration functions
|
|
register/unregister each transformation in the given array of
|
|
length count. They handle errors as follows:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
crypto_register_algs() succeeds if and only if it
|
|
successfully registers all the given transformations. If an
|
|
error occurs partway through, then it rolls back successful
|
|
registrations before returning the error code. Note that if
|
|
a driver needs to handle registration errors for individual
|
|
transformations, then it will need to use the non-bulk
|
|
function crypto_register_alg() instead.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
crypto_unregister_algs() tries to unregister all the given
|
|
transformations, continuing on error. It logs errors and
|
|
always returns zero.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
</sect1>
|
|
|
|
<sect1><title>Single-Block Symmetric Ciphers [CIPHER]</title>
|
|
<para>
|
|
Example of transformations: aes, arc4, ...
|
|
</para>
|
|
|
|
<para>
|
|
This section describes the simplest of all transformation
|
|
implementations, that being the CIPHER type used for symmetric
|
|
ciphers. The CIPHER type is used for transformations which
|
|
operate on exactly one block at a time and there are no
|
|
dependencies between blocks at all.
|
|
</para>
|
|
|
|
<sect2><title>Registration specifics</title>
|
|
<para>
|
|
The registration of [CIPHER] algorithm is specific in that
|
|
struct crypto_alg field .cra_type is empty. The .cra_u.cipher
|
|
has to be filled in with proper callbacks to implement this
|
|
transformation.
|
|
</para>
|
|
|
|
<para>
|
|
See struct cipher_alg below.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2><title>Cipher Definition With struct cipher_alg</title>
|
|
<para>
|
|
Struct cipher_alg defines a single block cipher.
|
|
</para>
|
|
|
|
<para>
|
|
Here are schematics of how these functions are called when
|
|
operated from other part of the kernel. Note that the
|
|
.cia_setkey() call might happen before or after any of these
|
|
schematics happen, but must not happen during any of these
|
|
are in-flight.
|
|
</para>
|
|
|
|
<para>
|
|
<programlisting>
|
|
KEY ---. PLAINTEXT ---.
|
|
v v
|
|
.cia_setkey() -> .cia_encrypt()
|
|
|
|
|
'-----> CIPHERTEXT
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Please note that a pattern where .cia_setkey() is called
|
|
multiple times is also valid:
|
|
</para>
|
|
|
|
<para>
|
|
<programlisting>
|
|
|
|
KEY1 --. PLAINTEXT1 --. KEY2 --. PLAINTEXT2 --.
|
|
v v v v
|
|
.cia_setkey() -> .cia_encrypt() -> .cia_setkey() -> .cia_encrypt()
|
|
| |
|
|
'---> CIPHERTEXT1 '---> CIPHERTEXT2
|
|
</programlisting>
|
|
</para>
|
|
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1><title>Multi-Block Ciphers</title>
|
|
<para>
|
|
Example of transformations: cbc(aes), ecb(arc4), ...
|
|
</para>
|
|
|
|
<para>
|
|
This section describes the multi-block cipher transformation
|
|
implementations. The multi-block ciphers are
|
|
used for transformations which operate on scatterlists of
|
|
data supplied to the transformation functions. They output
|
|
the result into a scatterlist of data as well.
|
|
</para>
|
|
|
|
<sect2><title>Registration Specifics</title>
|
|
|
|
<para>
|
|
The registration of multi-block cipher algorithms
|
|
is one of the most standard procedures throughout the crypto API.
|
|
</para>
|
|
|
|
<para>
|
|
Note, if a cipher implementation requires a proper alignment
|
|
of data, the caller should use the functions of
|
|
crypto_skcipher_alignmask() to identify a memory alignment mask.
|
|
The kernel crypto API is able to process requests that are unaligned.
|
|
This implies, however, additional overhead as the kernel
|
|
crypto API needs to perform the realignment of the data which
|
|
may imply moving of data.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2><title>Cipher Definition With struct blkcipher_alg and ablkcipher_alg</title>
|
|
<para>
|
|
Struct blkcipher_alg defines a synchronous block cipher whereas
|
|
struct ablkcipher_alg defines an asynchronous block cipher.
|
|
</para>
|
|
|
|
<para>
|
|
Please refer to the single block cipher description for schematics
|
|
of the block cipher usage.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2><title>Specifics Of Asynchronous Multi-Block Cipher</title>
|
|
<para>
|
|
There are a couple of specifics to the asynchronous interface.
|
|
</para>
|
|
|
|
<para>
|
|
First of all, some of the drivers will want to use the
|
|
Generic ScatterWalk in case the hardware needs to be fed
|
|
separate chunks of the scatterlist which contains the
|
|
plaintext and will contain the ciphertext. Please refer
|
|
to the ScatterWalk interface offered by the Linux kernel
|
|
scatter / gather list implementation.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1><title>Hashing [HASH]</title>
|
|
|
|
<para>
|
|
Example of transformations: crc32, md5, sha1, sha256,...
|
|
</para>
|
|
|
|
<sect2><title>Registering And Unregistering The Transformation</title>
|
|
|
|
<para>
|
|
There are multiple ways to register a HASH transformation,
|
|
depending on whether the transformation is synchronous [SHASH]
|
|
or asynchronous [AHASH] and the amount of HASH transformations
|
|
we are registering. You can find the prototypes defined in
|
|
include/crypto/internal/hash.h:
|
|
</para>
|
|
|
|
<programlisting>
|
|
int crypto_register_ahash(struct ahash_alg *alg);
|
|
|
|
int crypto_register_shash(struct shash_alg *alg);
|
|
int crypto_register_shashes(struct shash_alg *algs, int count);
|
|
</programlisting>
|
|
|
|
<para>
|
|
The respective counterparts for unregistering the HASH
|
|
transformation are as follows:
|
|
</para>
|
|
|
|
<programlisting>
|
|
int crypto_unregister_ahash(struct ahash_alg *alg);
|
|
|
|
int crypto_unregister_shash(struct shash_alg *alg);
|
|
int crypto_unregister_shashes(struct shash_alg *algs, int count);
|
|
</programlisting>
|
|
</sect2>
|
|
|
|
<sect2><title>Cipher Definition With struct shash_alg and ahash_alg</title>
|
|
<para>
|
|
Here are schematics of how these functions are called when
|
|
operated from other part of the kernel. Note that the .setkey()
|
|
call might happen before or after any of these schematics happen,
|
|
but must not happen during any of these are in-flight. Please note
|
|
that calling .init() followed immediately by .finish() is also a
|
|
perfectly valid transformation.
|
|
</para>
|
|
|
|
<programlisting>
|
|
I) DATA -----------.
|
|
v
|
|
.init() -> .update() -> .final() ! .update() might not be called
|
|
^ | | at all in this scenario.
|
|
'----' '---> HASH
|
|
|
|
II) DATA -----------.-----------.
|
|
v v
|
|
.init() -> .update() -> .finup() ! .update() may not be called
|
|
^ | | at all in this scenario.
|
|
'----' '---> HASH
|
|
|
|
III) DATA -----------.
|
|
v
|
|
.digest() ! The entire process is handled
|
|
| by the .digest() call.
|
|
'---------------> HASH
|
|
</programlisting>
|
|
|
|
<para>
|
|
Here is a schematic of how the .export()/.import() functions are
|
|
called when used from another part of the kernel.
|
|
</para>
|
|
|
|
<programlisting>
|
|
KEY--. DATA--.
|
|
v v ! .update() may not be called
|
|
.setkey() -> .init() -> .update() -> .export() at all in this scenario.
|
|
^ | |
|
|
'-----' '--> PARTIAL_HASH
|
|
|
|
----------- other transformations happen here -----------
|
|
|
|
PARTIAL_HASH--. DATA1--.
|
|
v v
|
|
.import -> .update() -> .final() ! .update() may not be called
|
|
^ | | at all in this scenario.
|
|
'----' '--> HASH1
|
|
|
|
PARTIAL_HASH--. DATA2-.
|
|
v v
|
|
.import -> .finup()
|
|
|
|
|
'---------------> HASH2
|
|
</programlisting>
|
|
</sect2>
|
|
|
|
<sect2><title>Specifics Of Asynchronous HASH Transformation</title>
|
|
<para>
|
|
Some of the drivers will want to use the Generic ScatterWalk
|
|
in case the implementation needs to be fed separate chunks of the
|
|
scatterlist which contains the input data. The buffer containing
|
|
the resulting hash will always be properly aligned to
|
|
.cra_alignmask so there is no need to worry about this.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<chapter id="User"><title>User Space Interface</title>
|
|
<sect1><title>Introduction</title>
|
|
<para>
|
|
The concepts of the kernel crypto API visible to kernel space is fully
|
|
applicable to the user space interface as well. Therefore, the kernel
|
|
crypto API high level discussion for the in-kernel use cases applies
|
|
here as well.
|
|
</para>
|
|
|
|
<para>
|
|
The major difference, however, is that user space can only act as a
|
|
consumer and never as a provider of a transformation or cipher algorithm.
|
|
</para>
|
|
|
|
<para>
|
|
The following covers the user space interface exported by the kernel
|
|
crypto API. A working example of this description is libkcapi that
|
|
can be obtained from [1]. That library can be used by user space
|
|
applications that require cryptographic services from the kernel.
|
|
</para>
|
|
|
|
<para>
|
|
Some details of the in-kernel kernel crypto API aspects do not
|
|
apply to user space, however. This includes the difference between
|
|
synchronous and asynchronous invocations. The user space API call
|
|
is fully synchronous.
|
|
</para>
|
|
|
|
<para>
|
|
[1] <ulink url="http://www.chronox.de/libkcapi.html">http://www.chronox.de/libkcapi.html</ulink>
|
|
</para>
|
|
|
|
</sect1>
|
|
|
|
<sect1><title>User Space API General Remarks</title>
|
|
<para>
|
|
The kernel crypto API is accessible from user space. Currently,
|
|
the following ciphers are accessible:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Message digest including keyed message digest (HMAC, CMAC)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Symmetric ciphers</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>AEAD ciphers</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Random Number Generators</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The interface is provided via socket type using the type AF_ALG.
|
|
In addition, the setsockopt option type is SOL_ALG. In case the
|
|
user space header files do not export these flags yet, use the
|
|
following macros:
|
|
</para>
|
|
|
|
<programlisting>
|
|
#ifndef AF_ALG
|
|
#define AF_ALG 38
|
|
#endif
|
|
#ifndef SOL_ALG
|
|
#define SOL_ALG 279
|
|
#endif
|
|
</programlisting>
|
|
|
|
<para>
|
|
A cipher is accessed with the same name as done for the in-kernel
|
|
API calls. This includes the generic vs. unique naming schema for
|
|
ciphers as well as the enforcement of priorities for generic names.
|
|
</para>
|
|
|
|
<para>
|
|
To interact with the kernel crypto API, a socket must be
|
|
created by the user space application. User space invokes the cipher
|
|
operation with the send()/write() system call family. The result of the
|
|
cipher operation is obtained with the read()/recv() system call family.
|
|
</para>
|
|
|
|
<para>
|
|
The following API calls assume that the socket descriptor
|
|
is already opened by the user space application and discusses only
|
|
the kernel crypto API specific invocations.
|
|
</para>
|
|
|
|
<para>
|
|
To initialize the socket interface, the following sequence has to
|
|
be performed by the consumer:
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
Create a socket of type AF_ALG with the struct sockaddr_alg
|
|
parameter specified below for the different cipher types.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Invoke bind with the socket descriptor
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Invoke accept with the socket descriptor. The accept system call
|
|
returns a new file descriptor that is to be used to interact with
|
|
the particular cipher instance. When invoking send/write or recv/read
|
|
system calls to send data to the kernel or obtain data from the
|
|
kernel, the file descriptor returned by accept must be used.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</sect1>
|
|
|
|
<sect1><title>In-place Cipher operation</title>
|
|
<para>
|
|
Just like the in-kernel operation of the kernel crypto API, the user
|
|
space interface allows the cipher operation in-place. That means that
|
|
the input buffer used for the send/write system call and the output
|
|
buffer used by the read/recv system call may be one and the same.
|
|
This is of particular interest for symmetric cipher operations where a
|
|
copying of the output data to its final destination can be avoided.
|
|
</para>
|
|
|
|
<para>
|
|
If a consumer on the other hand wants to maintain the plaintext and
|
|
the ciphertext in different memory locations, all a consumer needs
|
|
to do is to provide different memory pointers for the encryption and
|
|
decryption operation.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1><title>Message Digest API</title>
|
|
<para>
|
|
The message digest type to be used for the cipher operation is
|
|
selected when invoking the bind syscall. bind requires the caller
|
|
to provide a filled struct sockaddr data structure. This data
|
|
structure must be filled as follows:
|
|
</para>
|
|
|
|
<programlisting>
|
|
struct sockaddr_alg sa = {
|
|
.salg_family = AF_ALG,
|
|
.salg_type = "hash", /* this selects the hash logic in the kernel */
|
|
.salg_name = "sha1" /* this is the cipher name */
|
|
};
|
|
</programlisting>
|
|
|
|
<para>
|
|
The salg_type value "hash" applies to message digests and keyed
|
|
message digests. Though, a keyed message digest is referenced by
|
|
the appropriate salg_name. Please see below for the setsockopt
|
|
interface that explains how the key can be set for a keyed message
|
|
digest.
|
|
</para>
|
|
|
|
<para>
|
|
Using the send() system call, the application provides the data that
|
|
should be processed with the message digest. The send system call
|
|
allows the following flags to be specified:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
MSG_MORE: If this flag is set, the send system call acts like a
|
|
message digest update function where the final hash is not
|
|
yet calculated. If the flag is not set, the send system call
|
|
calculates the final message digest immediately.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
With the recv() system call, the application can read the message
|
|
digest from the kernel crypto API. If the buffer is too small for the
|
|
message digest, the flag MSG_TRUNC is set by the kernel.
|
|
</para>
|
|
|
|
<para>
|
|
In order to set a message digest key, the calling application must use
|
|
the setsockopt() option of ALG_SET_KEY. If the key is not set the HMAC
|
|
operation is performed without the initial HMAC state change caused by
|
|
the key.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1><title>Symmetric Cipher API</title>
|
|
<para>
|
|
The operation is very similar to the message digest discussion.
|
|
During initialization, the struct sockaddr data structure must be
|
|
filled as follows:
|
|
</para>
|
|
|
|
<programlisting>
|
|
struct sockaddr_alg sa = {
|
|
.salg_family = AF_ALG,
|
|
.salg_type = "skcipher", /* this selects the symmetric cipher */
|
|
.salg_name = "cbc(aes)" /* this is the cipher name */
|
|
};
|
|
</programlisting>
|
|
|
|
<para>
|
|
Before data can be sent to the kernel using the write/send system
|
|
call family, the consumer must set the key. The key setting is
|
|
described with the setsockopt invocation below.
|
|
</para>
|
|
|
|
<para>
|
|
Using the sendmsg() system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is
|
|
specified with the data structure provided by the sendmsg() system call.
|
|
</para>
|
|
|
|
<para>
|
|
The sendmsg system call parameter of struct msghdr is embedded into the
|
|
struct cmsghdr data structure. See recv(2) and cmsg(3) for more
|
|
information on how the cmsghdr data structure is used together with the
|
|
send/recv system call family. That cmsghdr data structure holds the
|
|
following information specified with a separate header instances:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
specification of the cipher operation type with one of these flags:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>ALG_OP_ENCRYPT - encryption of data</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>ALG_OP_DECRYPT - decryption of data</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
specification of the IV information marked with the flag ALG_SET_IV
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The send system call family allows the following flag to be specified:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
MSG_MORE: If this flag is set, the send system call acts like a
|
|
cipher update function where more input data is expected
|
|
with a subsequent invocation of the send system call.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
Note: The kernel reports -EINVAL for any unexpected data. The caller
|
|
must make sure that all data matches the constraints given in
|
|
/proc/crypto for the selected cipher.
|
|
</para>
|
|
|
|
<para>
|
|
With the recv() system call, the application can read the result of
|
|
the cipher operation from the kernel crypto API. The output buffer
|
|
must be at least as large as to hold all blocks of the encrypted or
|
|
decrypted data. If the output data size is smaller, only as many
|
|
blocks are returned that fit into that output buffer size.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1><title>AEAD Cipher API</title>
|
|
<para>
|
|
The operation is very similar to the symmetric cipher discussion.
|
|
During initialization, the struct sockaddr data structure must be
|
|
filled as follows:
|
|
</para>
|
|
|
|
<programlisting>
|
|
struct sockaddr_alg sa = {
|
|
.salg_family = AF_ALG,
|
|
.salg_type = "aead", /* this selects the symmetric cipher */
|
|
.salg_name = "gcm(aes)" /* this is the cipher name */
|
|
};
|
|
</programlisting>
|
|
|
|
<para>
|
|
Before data can be sent to the kernel using the write/send system
|
|
call family, the consumer must set the key. The key setting is
|
|
described with the setsockopt invocation below.
|
|
</para>
|
|
|
|
<para>
|
|
In addition, before data can be sent to the kernel using the
|
|
write/send system call family, the consumer must set the authentication
|
|
tag size. To set the authentication tag size, the caller must use the
|
|
setsockopt invocation described below.
|
|
</para>
|
|
|
|
<para>
|
|
Using the sendmsg() system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is
|
|
specified with the data structure provided by the sendmsg() system call.
|
|
</para>
|
|
|
|
<para>
|
|
The sendmsg system call parameter of struct msghdr is embedded into the
|
|
struct cmsghdr data structure. See recv(2) and cmsg(3) for more
|
|
information on how the cmsghdr data structure is used together with the
|
|
send/recv system call family. That cmsghdr data structure holds the
|
|
following information specified with a separate header instances:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
specification of the cipher operation type with one of these flags:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>ALG_OP_ENCRYPT - encryption of data</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>ALG_OP_DECRYPT - decryption of data</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
specification of the IV information marked with the flag ALG_SET_IV
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
specification of the associated authentication data (AAD) with the
|
|
flag ALG_SET_AEAD_ASSOCLEN. The AAD is sent to the kernel together
|
|
with the plaintext / ciphertext. See below for the memory structure.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The send system call family allows the following flag to be specified:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
MSG_MORE: If this flag is set, the send system call acts like a
|
|
cipher update function where more input data is expected
|
|
with a subsequent invocation of the send system call.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
Note: The kernel reports -EINVAL for any unexpected data. The caller
|
|
must make sure that all data matches the constraints given in
|
|
/proc/crypto for the selected cipher.
|
|
</para>
|
|
|
|
<para>
|
|
With the recv() system call, the application can read the result of
|
|
the cipher operation from the kernel crypto API. The output buffer
|
|
must be at least as large as defined with the memory structure below.
|
|
If the output data size is smaller, the cipher operation is not performed.
|
|
</para>
|
|
|
|
<para>
|
|
The authenticated decryption operation may indicate an integrity error.
|
|
Such breach in integrity is marked with the -EBADMSG error code.
|
|
</para>
|
|
|
|
<sect2><title>AEAD Memory Structure</title>
|
|
<para>
|
|
The AEAD cipher operates with the following information that
|
|
is communicated between user and kernel space as one data stream:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>plaintext or ciphertext</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>associated authentication data (AAD)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>authentication tag</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The sizes of the AAD and the authentication tag are provided with
|
|
the sendmsg and setsockopt calls (see there). As the kernel knows
|
|
the size of the entire data stream, the kernel is now able to
|
|
calculate the right offsets of the data components in the data
|
|
stream.
|
|
</para>
|
|
|
|
<para>
|
|
The user space caller must arrange the aforementioned information
|
|
in the following order:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
AEAD encryption input: AAD || plaintext
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
AEAD decryption input: AAD || ciphertext || authentication tag
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The output buffer the user space caller provides must be at least as
|
|
large to hold the following data:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
AEAD encryption output: ciphertext || authentication tag
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
AEAD decryption output: plaintext
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1><title>Random Number Generator API</title>
|
|
<para>
|
|
Again, the operation is very similar to the other APIs.
|
|
During initialization, the struct sockaddr data structure must be
|
|
filled as follows:
|
|
</para>
|
|
|
|
<programlisting>
|
|
struct sockaddr_alg sa = {
|
|
.salg_family = AF_ALG,
|
|
.salg_type = "rng", /* this selects the symmetric cipher */
|
|
.salg_name = "drbg_nopr_sha256" /* this is the cipher name */
|
|
};
|
|
</programlisting>
|
|
|
|
<para>
|
|
Depending on the RNG type, the RNG must be seeded. The seed is provided
|
|
using the setsockopt interface to set the key. For example, the
|
|
ansi_cprng requires a seed. The DRBGs do not require a seed, but
|
|
may be seeded.
|
|
</para>
|
|
|
|
<para>
|
|
Using the read()/recvmsg() system calls, random numbers can be obtained.
|
|
The kernel generates at most 128 bytes in one call. If user space
|
|
requires more data, multiple calls to read()/recvmsg() must be made.
|
|
</para>
|
|
|
|
<para>
|
|
WARNING: The user space caller may invoke the initially mentioned
|
|
accept system call multiple times. In this case, the returned file
|
|
descriptors have the same state.
|
|
</para>
|
|
|
|
</sect1>
|
|
|
|
<sect1><title>Zero-Copy Interface</title>
|
|
<para>
|
|
In addition to the send/write/read/recv system call family, the AF_ALG
|
|
interface can be accessed with the zero-copy interface of splice/vmsplice.
|
|
As the name indicates, the kernel tries to avoid a copy operation into
|
|
kernel space.
|
|
</para>
|
|
|
|
<para>
|
|
The zero-copy operation requires data to be aligned at the page boundary.
|
|
Non-aligned data can be used as well, but may require more operations of
|
|
the kernel which would defeat the speed gains obtained from the zero-copy
|
|
interface.
|
|
</para>
|
|
|
|
<para>
|
|
The system-interent limit for the size of one zero-copy operation is
|
|
16 pages. If more data is to be sent to AF_ALG, user space must slice
|
|
the input into segments with a maximum size of 16 pages.
|
|
</para>
|
|
|
|
<para>
|
|
Zero-copy can be used with the following code example (a complete working
|
|
example is provided with libkcapi):
|
|
</para>
|
|
|
|
<programlisting>
|
|
int pipes[2];
|
|
|
|
pipe(pipes);
|
|
/* input data in iov */
|
|
vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT);
|
|
/* opfd is the file descriptor returned from accept() system call */
|
|
splice(pipes[0], NULL, opfd, NULL, ret, 0);
|
|
read(opfd, out, outlen);
|
|
</programlisting>
|
|
|
|
</sect1>
|
|
|
|
<sect1><title>Setsockopt Interface</title>
|
|
<para>
|
|
In addition to the read/recv and send/write system call handling
|
|
to send and retrieve data subject to the cipher operation, a consumer
|
|
also needs to set the additional information for the cipher operation.
|
|
This additional information is set using the setsockopt system call
|
|
that must be invoked with the file descriptor of the open cipher
|
|
(i.e. the file descriptor returned by the accept system call).
|
|
</para>
|
|
|
|
<para>
|
|
Each setsockopt invocation must use the level SOL_ALG.
|
|
</para>
|
|
|
|
<para>
|
|
The setsockopt interface allows setting the following data using
|
|
the mentioned optname:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
ALG_SET_KEY -- Setting the key. Key setting is applicable to:
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>the skcipher cipher type (symmetric ciphers)</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>the hash cipher type (keyed message digests)</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>the AEAD cipher type</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>the RNG cipher type to provide the seed</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
ALG_SET_AEAD_AUTHSIZE -- Setting the authentication tag size
|
|
for AEAD ciphers. For a encryption operation, the authentication
|
|
tag of the given size will be generated. For a decryption operation,
|
|
the provided ciphertext is assumed to contain an authentication tag
|
|
of the given size (see section about AEAD memory layout below).
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
</sect1>
|
|
|
|
<sect1><title>User space API example</title>
|
|
<para>
|
|
Please see [1] for libkcapi which provides an easy-to-use wrapper
|
|
around the aforementioned Netlink kernel interface. [1] also contains
|
|
a test application that invokes all libkcapi API calls.
|
|
</para>
|
|
|
|
<para>
|
|
[1] <ulink url="http://www.chronox.de/libkcapi.html">http://www.chronox.de/libkcapi.html</ulink>
|
|
</para>
|
|
|
|
</sect1>
|
|
|
|
</chapter>
|
|
|
|
<chapter id="API"><title>Programming Interface</title>
|
|
<para>
|
|
Please note that the kernel crypto API contains the AEAD givcrypt
|
|
API (crypto_aead_giv* and aead_givcrypt_* function calls in
|
|
include/crypto/aead.h). This API is obsolete and will be removed
|
|
in the future. To obtain the functionality of an AEAD cipher with
|
|
internal IV generation, use the IV generator as a regular cipher.
|
|
For example, rfc4106(gcm(aes)) is the AEAD cipher with external
|
|
IV generation and seqniv(rfc4106(gcm(aes))) implies that the kernel
|
|
crypto API generates the IV. Different IV generators are available.
|
|
</para>
|
|
<sect1><title>Block Cipher Context Data Structures</title>
|
|
!Pinclude/linux/crypto.h Block Cipher Context Data Structures
|
|
!Finclude/crypto/aead.h aead_request
|
|
</sect1>
|
|
<sect1><title>Block Cipher Algorithm Definitions</title>
|
|
!Pinclude/linux/crypto.h Block Cipher Algorithm Definitions
|
|
!Finclude/linux/crypto.h crypto_alg
|
|
!Finclude/linux/crypto.h ablkcipher_alg
|
|
!Finclude/crypto/aead.h aead_alg
|
|
!Finclude/linux/crypto.h blkcipher_alg
|
|
!Finclude/linux/crypto.h cipher_alg
|
|
!Finclude/crypto/rng.h rng_alg
|
|
</sect1>
|
|
<sect1><title>Symmetric Key Cipher API</title>
|
|
!Pinclude/crypto/skcipher.h Symmetric Key Cipher API
|
|
!Finclude/crypto/skcipher.h crypto_alloc_skcipher
|
|
!Finclude/crypto/skcipher.h crypto_free_skcipher
|
|
!Finclude/crypto/skcipher.h crypto_has_skcipher
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_ivsize
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_blocksize
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_setkey
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_reqtfm
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_encrypt
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_decrypt
|
|
</sect1>
|
|
<sect1><title>Symmetric Key Cipher Request Handle</title>
|
|
!Pinclude/crypto/skcipher.h Symmetric Key Cipher Request Handle
|
|
!Finclude/crypto/skcipher.h crypto_skcipher_reqsize
|
|
!Finclude/crypto/skcipher.h skcipher_request_set_tfm
|
|
!Finclude/crypto/skcipher.h skcipher_request_alloc
|
|
!Finclude/crypto/skcipher.h skcipher_request_free
|
|
!Finclude/crypto/skcipher.h skcipher_request_set_callback
|
|
!Finclude/crypto/skcipher.h skcipher_request_set_crypt
|
|
</sect1>
|
|
<sect1><title>Asynchronous Block Cipher API - Deprecated</title>
|
|
!Pinclude/linux/crypto.h Asynchronous Block Cipher API
|
|
!Finclude/linux/crypto.h crypto_alloc_ablkcipher
|
|
!Finclude/linux/crypto.h crypto_free_ablkcipher
|
|
!Finclude/linux/crypto.h crypto_has_ablkcipher
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_ivsize
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_blocksize
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_setkey
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_reqtfm
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_encrypt
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_decrypt
|
|
</sect1>
|
|
<sect1><title>Asynchronous Cipher Request Handle - Deprecated</title>
|
|
!Pinclude/linux/crypto.h Asynchronous Cipher Request Handle
|
|
!Finclude/linux/crypto.h crypto_ablkcipher_reqsize
|
|
!Finclude/linux/crypto.h ablkcipher_request_set_tfm
|
|
!Finclude/linux/crypto.h ablkcipher_request_alloc
|
|
!Finclude/linux/crypto.h ablkcipher_request_free
|
|
!Finclude/linux/crypto.h ablkcipher_request_set_callback
|
|
!Finclude/linux/crypto.h ablkcipher_request_set_crypt
|
|
</sect1>
|
|
<sect1><title>Authenticated Encryption With Associated Data (AEAD) Cipher API</title>
|
|
!Pinclude/crypto/aead.h Authenticated Encryption With Associated Data (AEAD) Cipher API
|
|
!Finclude/crypto/aead.h crypto_alloc_aead
|
|
!Finclude/crypto/aead.h crypto_free_aead
|
|
!Finclude/crypto/aead.h crypto_aead_ivsize
|
|
!Finclude/crypto/aead.h crypto_aead_authsize
|
|
!Finclude/crypto/aead.h crypto_aead_blocksize
|
|
!Finclude/crypto/aead.h crypto_aead_setkey
|
|
!Finclude/crypto/aead.h crypto_aead_setauthsize
|
|
!Finclude/crypto/aead.h crypto_aead_encrypt
|
|
!Finclude/crypto/aead.h crypto_aead_decrypt
|
|
</sect1>
|
|
<sect1><title>Asynchronous AEAD Request Handle</title>
|
|
!Pinclude/crypto/aead.h Asynchronous AEAD Request Handle
|
|
!Finclude/crypto/aead.h crypto_aead_reqsize
|
|
!Finclude/crypto/aead.h aead_request_set_tfm
|
|
!Finclude/crypto/aead.h aead_request_alloc
|
|
!Finclude/crypto/aead.h aead_request_free
|
|
!Finclude/crypto/aead.h aead_request_set_callback
|
|
!Finclude/crypto/aead.h aead_request_set_crypt
|
|
!Finclude/crypto/aead.h aead_request_set_ad
|
|
</sect1>
|
|
<sect1><title>Synchronous Block Cipher API - Deprecated</title>
|
|
!Pinclude/linux/crypto.h Synchronous Block Cipher API
|
|
!Finclude/linux/crypto.h crypto_alloc_blkcipher
|
|
!Finclude/linux/crypto.h crypto_free_blkcipher
|
|
!Finclude/linux/crypto.h crypto_has_blkcipher
|
|
!Finclude/linux/crypto.h crypto_blkcipher_name
|
|
!Finclude/linux/crypto.h crypto_blkcipher_ivsize
|
|
!Finclude/linux/crypto.h crypto_blkcipher_blocksize
|
|
!Finclude/linux/crypto.h crypto_blkcipher_setkey
|
|
!Finclude/linux/crypto.h crypto_blkcipher_encrypt
|
|
!Finclude/linux/crypto.h crypto_blkcipher_encrypt_iv
|
|
!Finclude/linux/crypto.h crypto_blkcipher_decrypt
|
|
!Finclude/linux/crypto.h crypto_blkcipher_decrypt_iv
|
|
!Finclude/linux/crypto.h crypto_blkcipher_set_iv
|
|
!Finclude/linux/crypto.h crypto_blkcipher_get_iv
|
|
</sect1>
|
|
<sect1><title>Single Block Cipher API</title>
|
|
!Pinclude/linux/crypto.h Single Block Cipher API
|
|
!Finclude/linux/crypto.h crypto_alloc_cipher
|
|
!Finclude/linux/crypto.h crypto_free_cipher
|
|
!Finclude/linux/crypto.h crypto_has_cipher
|
|
!Finclude/linux/crypto.h crypto_cipher_blocksize
|
|
!Finclude/linux/crypto.h crypto_cipher_setkey
|
|
!Finclude/linux/crypto.h crypto_cipher_encrypt_one
|
|
!Finclude/linux/crypto.h crypto_cipher_decrypt_one
|
|
</sect1>
|
|
<sect1><title>Message Digest Algorithm Definitions</title>
|
|
!Pinclude/crypto/hash.h Message Digest Algorithm Definitions
|
|
!Finclude/crypto/hash.h hash_alg_common
|
|
!Finclude/crypto/hash.h ahash_alg
|
|
!Finclude/crypto/hash.h shash_alg
|
|
</sect1>
|
|
<sect1><title>Asynchronous Message Digest API</title>
|
|
!Pinclude/crypto/hash.h Asynchronous Message Digest API
|
|
!Finclude/crypto/hash.h crypto_alloc_ahash
|
|
!Finclude/crypto/hash.h crypto_free_ahash
|
|
!Finclude/crypto/hash.h crypto_ahash_init
|
|
!Finclude/crypto/hash.h crypto_ahash_digestsize
|
|
!Finclude/crypto/hash.h crypto_ahash_reqtfm
|
|
!Finclude/crypto/hash.h crypto_ahash_reqsize
|
|
!Finclude/crypto/hash.h crypto_ahash_setkey
|
|
!Finclude/crypto/hash.h crypto_ahash_finup
|
|
!Finclude/crypto/hash.h crypto_ahash_final
|
|
!Finclude/crypto/hash.h crypto_ahash_digest
|
|
!Finclude/crypto/hash.h crypto_ahash_export
|
|
!Finclude/crypto/hash.h crypto_ahash_import
|
|
</sect1>
|
|
<sect1><title>Asynchronous Hash Request Handle</title>
|
|
!Pinclude/crypto/hash.h Asynchronous Hash Request Handle
|
|
!Finclude/crypto/hash.h ahash_request_set_tfm
|
|
!Finclude/crypto/hash.h ahash_request_alloc
|
|
!Finclude/crypto/hash.h ahash_request_free
|
|
!Finclude/crypto/hash.h ahash_request_set_callback
|
|
!Finclude/crypto/hash.h ahash_request_set_crypt
|
|
</sect1>
|
|
<sect1><title>Synchronous Message Digest API</title>
|
|
!Pinclude/crypto/hash.h Synchronous Message Digest API
|
|
!Finclude/crypto/hash.h crypto_alloc_shash
|
|
!Finclude/crypto/hash.h crypto_free_shash
|
|
!Finclude/crypto/hash.h crypto_shash_blocksize
|
|
!Finclude/crypto/hash.h crypto_shash_digestsize
|
|
!Finclude/crypto/hash.h crypto_shash_descsize
|
|
!Finclude/crypto/hash.h crypto_shash_setkey
|
|
!Finclude/crypto/hash.h crypto_shash_digest
|
|
!Finclude/crypto/hash.h crypto_shash_export
|
|
!Finclude/crypto/hash.h crypto_shash_import
|
|
!Finclude/crypto/hash.h crypto_shash_init
|
|
!Finclude/crypto/hash.h crypto_shash_update
|
|
!Finclude/crypto/hash.h crypto_shash_final
|
|
!Finclude/crypto/hash.h crypto_shash_finup
|
|
</sect1>
|
|
<sect1><title>Crypto API Random Number API</title>
|
|
!Pinclude/crypto/rng.h Random number generator API
|
|
!Finclude/crypto/rng.h crypto_alloc_rng
|
|
!Finclude/crypto/rng.h crypto_rng_alg
|
|
!Finclude/crypto/rng.h crypto_free_rng
|
|
!Finclude/crypto/rng.h crypto_rng_generate
|
|
!Finclude/crypto/rng.h crypto_rng_get_bytes
|
|
!Finclude/crypto/rng.h crypto_rng_reset
|
|
!Finclude/crypto/rng.h crypto_rng_seedsize
|
|
!Cinclude/crypto/rng.h
|
|
</sect1>
|
|
<sect1><title>Asymmetric Cipher API</title>
|
|
!Pinclude/crypto/akcipher.h Generic Public Key API
|
|
!Finclude/crypto/akcipher.h akcipher_alg
|
|
!Finclude/crypto/akcipher.h akcipher_request
|
|
!Finclude/crypto/akcipher.h crypto_alloc_akcipher
|
|
!Finclude/crypto/akcipher.h crypto_free_akcipher
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_set_pub_key
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_set_priv_key
|
|
</sect1>
|
|
<sect1><title>Asymmetric Cipher Request Handle</title>
|
|
!Finclude/crypto/akcipher.h akcipher_request_alloc
|
|
!Finclude/crypto/akcipher.h akcipher_request_free
|
|
!Finclude/crypto/akcipher.h akcipher_request_set_callback
|
|
!Finclude/crypto/akcipher.h akcipher_request_set_crypt
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_maxsize
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_encrypt
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_decrypt
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_sign
|
|
!Finclude/crypto/akcipher.h crypto_akcipher_verify
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<chapter id="Code"><title>Code Examples</title>
|
|
<sect1><title>Code Example For Symmetric Key Cipher Operation</title>
|
|
<programlisting>
|
|
|
|
struct tcrypt_result {
|
|
struct completion completion;
|
|
int err;
|
|
};
|
|
|
|
/* tie all data structures together */
|
|
struct skcipher_def {
|
|
struct scatterlist sg;
|
|
struct crypto_skcipher *tfm;
|
|
struct skcipher_request *req;
|
|
struct tcrypt_result result;
|
|
};
|
|
|
|
/* Callback function */
|
|
static void test_skcipher_cb(struct crypto_async_request *req, int error)
|
|
{
|
|
struct tcrypt_result *result = req->data;
|
|
|
|
if (error == -EINPROGRESS)
|
|
return;
|
|
result->err = error;
|
|
complete(&result->completion);
|
|
pr_info("Encryption finished successfully\n");
|
|
}
|
|
|
|
/* Perform cipher operation */
|
|
static unsigned int test_skcipher_encdec(struct skcipher_def *sk,
|
|
int enc)
|
|
{
|
|
int rc = 0;
|
|
|
|
if (enc)
|
|
rc = crypto_skcipher_encrypt(sk->req);
|
|
else
|
|
rc = crypto_skcipher_decrypt(sk->req);
|
|
|
|
switch (rc) {
|
|
case 0:
|
|
break;
|
|
case -EINPROGRESS:
|
|
case -EBUSY:
|
|
rc = wait_for_completion_interruptible(
|
|
&sk->result.completion);
|
|
if (!rc && !sk->result.err) {
|
|
reinit_completion(&sk->result.completion);
|
|
break;
|
|
}
|
|
default:
|
|
pr_info("skcipher encrypt returned with %d result %d\n",
|
|
rc, sk->result.err);
|
|
break;
|
|
}
|
|
init_completion(&sk->result.completion);
|
|
|
|
return rc;
|
|
}
|
|
|
|
/* Initialize and trigger cipher operation */
|
|
static int test_skcipher(void)
|
|
{
|
|
struct skcipher_def sk;
|
|
struct crypto_skcipher *skcipher = NULL;
|
|
struct skcipher_request *req = NULL;
|
|
char *scratchpad = NULL;
|
|
char *ivdata = NULL;
|
|
unsigned char key[32];
|
|
int ret = -EFAULT;
|
|
|
|
skcipher = crypto_alloc_skcipher("cbc-aes-aesni", 0, 0);
|
|
if (IS_ERR(skcipher)) {
|
|
pr_info("could not allocate skcipher handle\n");
|
|
return PTR_ERR(skcipher);
|
|
}
|
|
|
|
req = skcipher_request_alloc(skcipher, GFP_KERNEL);
|
|
if (!req) {
|
|
pr_info("could not allocate skcipher request\n");
|
|
ret = -ENOMEM;
|
|
goto out;
|
|
}
|
|
|
|
skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
|
|
test_skcipher_cb,
|
|
&sk.result);
|
|
|
|
/* AES 256 with random key */
|
|
get_random_bytes(&key, 32);
|
|
if (crypto_skcipher_setkey(skcipher, key, 32)) {
|
|
pr_info("key could not be set\n");
|
|
ret = -EAGAIN;
|
|
goto out;
|
|
}
|
|
|
|
/* IV will be random */
|
|
ivdata = kmalloc(16, GFP_KERNEL);
|
|
if (!ivdata) {
|
|
pr_info("could not allocate ivdata\n");
|
|
goto out;
|
|
}
|
|
get_random_bytes(ivdata, 16);
|
|
|
|
/* Input data will be random */
|
|
scratchpad = kmalloc(16, GFP_KERNEL);
|
|
if (!scratchpad) {
|
|
pr_info("could not allocate scratchpad\n");
|
|
goto out;
|
|
}
|
|
get_random_bytes(scratchpad, 16);
|
|
|
|
sk.tfm = skcipher;
|
|
sk.req = req;
|
|
|
|
/* We encrypt one block */
|
|
sg_init_one(&sk.sg, scratchpad, 16);
|
|
skcipher_request_set_crypt(req, &sk.sg, &sk.sg, 16, ivdata);
|
|
init_completion(&sk.result.completion);
|
|
|
|
/* encrypt data */
|
|
ret = test_skcipher_encdec(&sk, 1);
|
|
if (ret)
|
|
goto out;
|
|
|
|
pr_info("Encryption triggered successfully\n");
|
|
|
|
out:
|
|
if (skcipher)
|
|
crypto_free_skcipher(skcipher);
|
|
if (req)
|
|
skcipher_request_free(req);
|
|
if (ivdata)
|
|
kfree(ivdata);
|
|
if (scratchpad)
|
|
kfree(scratchpad);
|
|
return ret;
|
|
}
|
|
</programlisting>
|
|
</sect1>
|
|
|
|
<sect1><title>Code Example For Use of Operational State Memory With SHASH</title>
|
|
<programlisting>
|
|
|
|
struct sdesc {
|
|
struct shash_desc shash;
|
|
char ctx[];
|
|
};
|
|
|
|
static struct sdescinit_sdesc(struct crypto_shash *alg)
|
|
{
|
|
struct sdescsdesc;
|
|
int size;
|
|
|
|
size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
|
|
sdesc = kmalloc(size, GFP_KERNEL);
|
|
if (!sdesc)
|
|
return ERR_PTR(-ENOMEM);
|
|
sdesc->shash.tfm = alg;
|
|
sdesc->shash.flags = 0x0;
|
|
return sdesc;
|
|
}
|
|
|
|
static int calc_hash(struct crypto_shashalg,
|
|
const unsigned chardata, unsigned int datalen,
|
|
unsigned chardigest) {
|
|
struct sdescsdesc;
|
|
int ret;
|
|
|
|
sdesc = init_sdesc(alg);
|
|
if (IS_ERR(sdesc)) {
|
|
pr_info("trusted_key: can't alloc %s\n", hash_alg);
|
|
return PTR_ERR(sdesc);
|
|
}
|
|
|
|
ret = crypto_shash_digest(&sdesc->shash, data, datalen, digest);
|
|
kfree(sdesc);
|
|
return ret;
|
|
}
|
|
</programlisting>
|
|
</sect1>
|
|
|
|
<sect1><title>Code Example For Random Number Generator Usage</title>
|
|
<programlisting>
|
|
|
|
static int get_random_numbers(u8 *buf, unsigned int len)
|
|
{
|
|
struct crypto_rngrng = NULL;
|
|
chardrbg = "drbg_nopr_sha256"; /* Hash DRBG with SHA-256, no PR */
|
|
int ret;
|
|
|
|
if (!buf || !len) {
|
|
pr_debug("No output buffer provided\n");
|
|
return -EINVAL;
|
|
}
|
|
|
|
rng = crypto_alloc_rng(drbg, 0, 0);
|
|
if (IS_ERR(rng)) {
|
|
pr_debug("could not allocate RNG handle for %s\n", drbg);
|
|
return -PTR_ERR(rng);
|
|
}
|
|
|
|
ret = crypto_rng_get_bytes(rng, buf, len);
|
|
if (ret < 0)
|
|
pr_debug("generation of random numbers failed\n");
|
|
else if (ret == 0)
|
|
pr_debug("RNG returned no data");
|
|
else
|
|
pr_debug("RNG returned %d bytes of data\n", ret);
|
|
|
|
out:
|
|
crypto_free_rng(rng);
|
|
return ret;
|
|
}
|
|
</programlisting>
|
|
</sect1>
|
|
</chapter>
|
|
</book>
|