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