// 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");