Commit 8dfa20fc authored by Eric Biggers's avatar Eric Biggers Committed by Herbert Xu
Browse files

crypto: ghash - add comment and improve help text 



To help avoid confusion, add a comment to ghash-generic.c which explains
the convention that the kernel's implementation of GHASH uses.

Also update the Kconfig help text and module descriptions to call GHASH
a "hash function" rather than a "message digest", since the latter
normally means a real cryptographic hash function, which GHASH is not.

Cc: Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: default avatarPascal Van Leeuwen <pvanleeuwen@verimatrix.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 065cf577

arch/arm/crypto/ghash-ce-glue.c

+1 −1
Original line number Diff line number Diff line
@@ -18,7 +18,7 @@ 
#include <linux/crypto.h>

#include <linux/module.h>



MODULE_DESCRIPTION("GHASH secure hash using ARMv8 Crypto Extensions");

MODULE_DESCRIPTION("GHASH hash function using ARMv8 Crypto Extensions");

MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");

MODULE_LICENSE("GPL v2");

MODULE_ALIAS_CRYPTO("ghash");

arch/s390/crypto/ghash_s390.c

+1 −1
Original line number Diff line number Diff line
@@ -153,4 +153,4 @@ module_exit(ghash_mod_exit); 
MODULE_ALIAS_CRYPTO("ghash");



MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("GHASH Message Digest Algorithm, s390 implementation");
 
MODULE_DESCRIPTION("GHASH hash function, s390 implementation");

arch/x86/crypto/ghash-clmulni-intel_glue.c

+1 −2
Original line number Diff line number Diff line
@@ -357,6 +357,5 @@ module_init(ghash_pclmulqdqni_mod_init); 
module_exit(ghash_pclmulqdqni_mod_exit);



MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("GHASH Message Digest Algorithm, "

		   "accelerated by PCLMULQDQ-NI");

MODULE_DESCRIPTION("GHASH hash function, accelerated by PCLMULQDQ-NI");

MODULE_ALIAS_CRYPTO("ghash");

crypto/Kconfig

+6 −5
Original line number Diff line number Diff line
@@ -647,11 +647,12 @@ config CRYPTO_VPMSUM_TESTER 
	  Unless you are testing these algorithms, you don't need this.



config CRYPTO_GHASH

	tristate "GHASH digest algorithm"

	tristate "GHASH hash function"

	select CRYPTO_GF128MUL

	select CRYPTO_HASH

	help

	  GHASH is message digest algorithm for GCM (Galois/Counter Mode).

	  GHASH is the hash function used in GCM (Galois/Counter Mode).

	  It is not a general-purpose cryptographic hash function.



config CRYPTO_POLY1305

	tristate "Poly1305 authenticator algorithm"
@@ -976,12 +977,12 @@ config CRYPTO_WP512 
	  <http://www.larc.usp.br/~pbarreto/WhirlpoolPage.html>



config CRYPTO_GHASH_CLMUL_NI_INTEL

	tristate "GHASH digest algorithm (CLMUL-NI accelerated)"

	tristate "GHASH hash function (CLMUL-NI accelerated)"

	depends on X86 && 64BIT

	select CRYPTO_CRYPTD

	help

	  GHASH is message digest algorithm for GCM (Galois/Counter Mode).

	  The implementation is accelerated by CLMUL-NI of Intel.

	  This is the x86_64 CLMUL-NI accelerated implementation of

	  GHASH, the hash function used in GCM (Galois/Counter mode).



comment "Ciphers"

crypto/ghash-generic.c

+28 −3
Original line number Diff line number Diff line 
// 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");

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