diff options
Diffstat (limited to 'crypto/ghash-generic.c')
| -rw-r--r-- | crypto/ghash-generic.c | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/crypto/ghash-generic.c b/crypto/ghash-generic.c index dad9e1f91a78..5027b3461c92 100644 --- a/crypto/ghash-generic.c +++ b/crypto/ghash-generic.c @@ -1,12 +1,37 @@ // SPDX-License-Identifier: GPL-2.0-only /* - * GHASH: digest algorithm for GCM (Galois/Counter Mode). + * GHASH: hash function for GCM (Galois/Counter Mode). * * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi> * Copyright (c) 2009 Intel Corp. * Author: Huang Ying <ying.huang@intel.com> + */ + +/* + * GHASH is a keyed hash function used in GCM authentication tag generation. + * + * The original GCM paper [1] presents GHASH as a function GHASH(H, A, C) which + * takes a 16-byte hash key H, additional authenticated data A, and a ciphertext + * C. It formats A and C into a single byte string X, interprets X as a + * polynomial over GF(2^128), and evaluates this polynomial at the point H. + * + * However, the NIST standard for GCM [2] presents GHASH as GHASH(H, X) where X + * is the already-formatted byte string containing both A and C. + * + * "ghash" in the Linux crypto API uses the 'X' (pre-formatted) convention, + * since the API supports only a single data stream per hash. Thus, the + * formatting of 'A' and 'C' is done in the "gcm" template, not in "ghash". + * + * The reason "ghash" is separate from "gcm" is to allow "gcm" to use an + * accelerated "ghash" when a standalone accelerated "gcm(aes)" is unavailable. + * It is generally inappropriate to use "ghash" for other purposes, since it is + * an "ε-almost-XOR-universal hash function", not a cryptographic hash function. + * It can only be used securely in crypto modes specially designed to use it. * - * The algorithm implementation is copied from gcm.c. + * [1] The Galois/Counter Mode of Operation (GCM) + * (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.694.695&rep=rep1&type=pdf) + * [2] Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC + * (https://csrc.nist.gov/publications/detail/sp/800-38d/final) */ #include <crypto/algapi.h> @@ -156,6 +181,6 @@ subsys_initcall(ghash_mod_init); module_exit(ghash_mod_exit); MODULE_LICENSE("GPL"); -MODULE_DESCRIPTION("GHASH Message Digest Algorithm"); +MODULE_DESCRIPTION("GHASH hash function"); MODULE_ALIAS_CRYPTO("ghash"); MODULE_ALIAS_CRYPTO("ghash-generic"); |