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), provide an abstraction to the underlying algorithms, and handle common logical operations (e.g. cipher modes, HMAC for digests). 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, digest.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 three types of transforms: Ciphers, Digests and Compressors. The compression algorithms especially seem to be performing very well so far. 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> struct scatterlist sg[2]; char result[128]; struct crypto_tfm *tfm; tfm = crypto_alloc_tfm("md5", 0); if (tfm == NULL) fail(); /* ... set up the scatterlists ... */ crypto_digest_init(tfm); crypto_digest_update(tfm, &sg, 2); crypto_digest_final(tfm, result); crypto_free_tfm(tfm); Many real examples are available in the regression test module (tcrypt.c). CONFIGURATION NOTES As Triple DES is part of the DES module, for those using modular builds, add the following line to /etc/modules.conf: alias des3_ede des The Null algorithms reside in the crypto_null module, so these lines should also be added: alias cipher_null crypto_null alias digest_null crypto_null alias compress_null crypto_null The SHA384 algorithm shares code within the SHA512 module, so you'll also need: alias sha384 sha512 DEVELOPER NOTES Transforms may only be allocated in user context, and cryptographic methods may only be called from softirq and user contexts. 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: James Morris <jmorris@intercode.com.au> Cc: David S. Miller <davem@redhat.com> FURTHER INFORMATION For further patches and various updates, including the current TODO list, see: http://samba.org/~jamesm/crypto/ AUTHORS James Morris David S. Miller 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 M�ller 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) SHA1 algorithm contributors: Jean-Francois Dive DES algorithm contributors: Raimar Falke Gisle S�lensminde Niels M�ller 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 CAST5 algorithm contributors: Kartikey Mahendra Bhatt (original developers unknown, FSF copyright). Generic scatterwalk code by Adam J. Richter <adam@yggdrasil.com> Please send any credits updates or corrections to: James Morris <jmorris@intercode.com.au>