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Fixed MTP to work with TWRP
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248
Documentation/crypto/api-intro.txt
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248
Documentation/crypto/api-intro.txt
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Scatterlist Cryptographic API
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INTRODUCTION
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The Scatterlist Crypto API takes page vectors (scatterlists) as
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arguments, and works directly on pages. In some cases (e.g. ECB
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mode ciphers), this will allow for pages to be encrypted in-place
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with no copying.
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One of the initial goals of this design was to readily support IPsec,
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so that processing can be applied to paged skb's without the need
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for linearization.
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DETAILS
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At the lowest level are algorithms, which register dynamically with the
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API.
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'Transforms' are user-instantiated objects, which maintain state, handle all
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of the implementation logic (e.g. manipulating page vectors) and provide an
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abstraction to the underlying algorithms. However, at the user
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level they are very simple.
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Conceptually, the API layering looks like this:
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[transform api] (user interface)
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[transform ops] (per-type logic glue e.g. cipher.c, compress.c)
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[algorithm api] (for registering algorithms)
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The idea is to make the user interface and algorithm registration API
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very simple, while hiding the core logic from both. Many good ideas
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from existing APIs such as Cryptoapi and Nettle have been adapted for this.
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The API currently supports five main types of transforms: AEAD (Authenticated
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Encryption with Associated Data), Block Ciphers, Ciphers, Compressors and
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Hashes.
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Please note that Block Ciphers is somewhat of a misnomer. It is in fact
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meant to support all ciphers including stream ciphers. The difference
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between Block Ciphers and Ciphers is that the latter operates on exactly
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one block while the former can operate on an arbitrary amount of data,
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subject to block size requirements (i.e., non-stream ciphers can only
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process multiples of blocks).
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Support for hardware crypto devices via an asynchronous interface is
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under development.
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Here's an example of how to use the API:
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#include <linux/crypto.h>
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#include <linux/err.h>
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#include <linux/scatterlist.h>
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struct scatterlist sg[2];
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char result[128];
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struct crypto_hash *tfm;
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struct hash_desc desc;
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tfm = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC);
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if (IS_ERR(tfm))
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fail();
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/* ... set up the scatterlists ... */
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desc.tfm = tfm;
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desc.flags = 0;
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if (crypto_hash_digest(&desc, sg, 2, result))
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fail();
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crypto_free_hash(tfm);
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Many real examples are available in the regression test module (tcrypt.c).
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DEVELOPER NOTES
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Transforms may only be allocated in user context, and cryptographic
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methods may only be called from softirq and user contexts. For
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transforms with a setkey method it too should only be called from
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user context.
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When using the API for ciphers, performance will be optimal if each
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scatterlist contains data which is a multiple of the cipher's block
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size (typically 8 bytes). This prevents having to do any copying
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across non-aligned page fragment boundaries.
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ADDING NEW ALGORITHMS
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When submitting a new algorithm for inclusion, a mandatory requirement
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is that at least a few test vectors from known sources (preferably
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standards) be included.
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Converting existing well known code is preferred, as it is more likely
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to have been reviewed and widely tested. If submitting code from LGPL
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sources, please consider changing the license to GPL (see section 3 of
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the LGPL).
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Algorithms submitted must also be generally patent-free (e.g. IDEA
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will not be included in the mainline until around 2011), and be based
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on a recognized standard and/or have been subjected to appropriate
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peer review.
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Also check for any RFCs which may relate to the use of specific algorithms,
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as well as general application notes such as RFC2451 ("The ESP CBC-Mode
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Cipher Algorithms").
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It's a good idea to avoid using lots of macros and use inlined functions
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instead, as gcc does a good job with inlining, while excessive use of
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macros can cause compilation problems on some platforms.
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Also check the TODO list at the web site listed below to see what people
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might already be working on.
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BUGS
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Send bug reports to:
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linux-crypto@vger.kernel.org
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Cc: Herbert Xu <herbert@gondor.apana.org.au>,
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David S. Miller <davem@redhat.com>
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FURTHER INFORMATION
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For further patches and various updates, including the current TODO
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list, see:
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http://gondor.apana.org.au/~herbert/crypto/
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AUTHORS
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James Morris
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David S. Miller
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Herbert Xu
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CREDITS
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The following people provided invaluable feedback during the development
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of the API:
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Alexey Kuznetzov
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Rusty Russell
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Herbert Valerio Riedel
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Jeff Garzik
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Michael Richardson
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Andrew Morton
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Ingo Oeser
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Christoph Hellwig
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Portions of this API were derived from the following projects:
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Kerneli Cryptoapi (http://www.kerneli.org/)
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Alexander Kjeldaas
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Herbert Valerio Riedel
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Kyle McMartin
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Jean-Luc Cooke
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David Bryson
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Clemens Fruhwirth
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Tobias Ringstrom
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Harald Welte
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and;
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Nettle (http://www.lysator.liu.se/~nisse/nettle/)
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Niels Möller
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Original developers of the crypto algorithms:
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Dana L. How (DES)
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Andrew Tridgell and Steve French (MD4)
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Colin Plumb (MD5)
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Steve Reid (SHA1)
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Jean-Luc Cooke (SHA256, SHA384, SHA512)
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Kazunori Miyazawa / USAGI (HMAC)
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Matthew Skala (Twofish)
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Dag Arne Osvik (Serpent)
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Brian Gladman (AES)
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Kartikey Mahendra Bhatt (CAST6)
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Jon Oberheide (ARC4)
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Jouni Malinen (Michael MIC)
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NTT(Nippon Telegraph and Telephone Corporation) (Camellia)
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SHA1 algorithm contributors:
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Jean-Francois Dive
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DES algorithm contributors:
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Raimar Falke
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Gisle Sælensminde
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Niels Möller
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Blowfish algorithm contributors:
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Herbert Valerio Riedel
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Kyle McMartin
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Twofish algorithm contributors:
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Werner Koch
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Marc Mutz
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SHA256/384/512 algorithm contributors:
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Andrew McDonald
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Kyle McMartin
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Herbert Valerio Riedel
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AES algorithm contributors:
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Alexander Kjeldaas
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Herbert Valerio Riedel
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Kyle McMartin
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Adam J. Richter
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Fruhwirth Clemens (i586)
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Linus Torvalds (i586)
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CAST5 algorithm contributors:
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Kartikey Mahendra Bhatt (original developers unknown, FSF copyright).
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TEA/XTEA algorithm contributors:
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Aaron Grothe
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Michael Ringe
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Khazad algorithm contributors:
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Aaron Grothe
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Whirlpool algorithm contributors:
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Aaron Grothe
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Jean-Luc Cooke
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Anubis algorithm contributors:
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Aaron Grothe
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Tiger algorithm contributors:
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Aaron Grothe
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VIA PadLock contributors:
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Michal Ludvig
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Camellia algorithm contributors:
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NTT(Nippon Telegraph and Telephone Corporation) (Camellia)
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Generic scatterwalk code by Adam J. Richter <adam@yggdrasil.com>
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Please send any credits updates or corrections to:
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Herbert Xu <herbert@gondor.apana.org.au>
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