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Diffstat (limited to '')
| -rw-r--r-- | crypto/ghash-generic.c | 184 |
1 files changed, 184 insertions, 0 deletions
diff --git a/crypto/ghash-generic.c b/crypto/ghash-generic.c new file mode 100644 index 000000000..c70d163c1 --- /dev/null +++ b/crypto/ghash-generic.c @@ -0,0 +1,184 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * 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. + * + * [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> +#include <crypto/gf128mul.h> +#include <crypto/ghash.h> +#include <crypto/internal/hash.h> +#include <linux/crypto.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/module.h> + +static int ghash_init(struct shash_desc *desc) +{ + struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); + + memset(dctx, 0, sizeof(*dctx)); + + return 0; +} + +static int ghash_setkey(struct crypto_shash *tfm, + const u8 *key, unsigned int keylen) +{ + struct ghash_ctx *ctx = crypto_shash_ctx(tfm); + be128 k; + + if (keylen != GHASH_BLOCK_SIZE) + return -EINVAL; + + if (ctx->gf128) + gf128mul_free_4k(ctx->gf128); + + BUILD_BUG_ON(sizeof(k) != GHASH_BLOCK_SIZE); + memcpy(&k, key, GHASH_BLOCK_SIZE); /* avoid violating alignment rules */ + ctx->gf128 = gf128mul_init_4k_lle(&k); + memzero_explicit(&k, GHASH_BLOCK_SIZE); + + if (!ctx->gf128) + return -ENOMEM; + + return 0; +} + +static int ghash_update(struct shash_desc *desc, + const u8 *src, unsigned int srclen) +{ + struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); + struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm); + u8 *dst = dctx->buffer; + + if (dctx->bytes) { + int n = min(srclen, dctx->bytes); + u8 *pos = dst + (GHASH_BLOCK_SIZE - dctx->bytes); + + dctx->bytes -= n; + srclen -= n; + + while (n--) + *pos++ ^= *src++; + + if (!dctx->bytes) + gf128mul_4k_lle((be128 *)dst, ctx->gf128); + } + + while (srclen >= GHASH_BLOCK_SIZE) { + crypto_xor(dst, src, GHASH_BLOCK_SIZE); + gf128mul_4k_lle((be128 *)dst, ctx->gf128); + src += GHASH_BLOCK_SIZE; + srclen -= GHASH_BLOCK_SIZE; + } + + if (srclen) { + dctx->bytes = GHASH_BLOCK_SIZE - srclen; + while (srclen--) + *dst++ ^= *src++; + } + + return 0; +} + +static void ghash_flush(struct ghash_ctx *ctx, struct ghash_desc_ctx *dctx) +{ + u8 *dst = dctx->buffer; + + if (dctx->bytes) { + u8 *tmp = dst + (GHASH_BLOCK_SIZE - dctx->bytes); + + while (dctx->bytes--) + *tmp++ ^= 0; + + gf128mul_4k_lle((be128 *)dst, ctx->gf128); + } + + dctx->bytes = 0; +} + +static int ghash_final(struct shash_desc *desc, u8 *dst) +{ + struct ghash_desc_ctx *dctx = shash_desc_ctx(desc); + struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm); + u8 *buf = dctx->buffer; + + ghash_flush(ctx, dctx); + memcpy(dst, buf, GHASH_BLOCK_SIZE); + + return 0; +} + +static void ghash_exit_tfm(struct crypto_tfm *tfm) +{ + struct ghash_ctx *ctx = crypto_tfm_ctx(tfm); + if (ctx->gf128) + gf128mul_free_4k(ctx->gf128); +} + +static struct shash_alg ghash_alg = { + .digestsize = GHASH_DIGEST_SIZE, + .init = ghash_init, + .update = ghash_update, + .final = ghash_final, + .setkey = ghash_setkey, + .descsize = sizeof(struct ghash_desc_ctx), + .base = { + .cra_name = "ghash", + .cra_driver_name = "ghash-generic", + .cra_priority = 100, + .cra_blocksize = GHASH_BLOCK_SIZE, + .cra_ctxsize = sizeof(struct ghash_ctx), + .cra_module = THIS_MODULE, + .cra_exit = ghash_exit_tfm, + }, +}; + +static int __init ghash_mod_init(void) +{ + return crypto_register_shash(&ghash_alg); +} + +static void __exit ghash_mod_exit(void) +{ + crypto_unregister_shash(&ghash_alg); +} + +subsys_initcall(ghash_mod_init); +module_exit(ghash_mod_exit); + +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("GHASH hash function"); +MODULE_ALIAS_CRYPTO("ghash"); +MODULE_ALIAS_CRYPTO("ghash-generic"); |