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Diffstat (limited to 'crypto/polyval-generic.c')
| -rw-r--r-- | crypto/polyval-generic.c | 245 |
1 files changed, 245 insertions, 0 deletions
diff --git a/crypto/polyval-generic.c b/crypto/polyval-generic.c new file mode 100644 index 000000000..16bfa6925 --- /dev/null +++ b/crypto/polyval-generic.c @@ -0,0 +1,245 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * POLYVAL: hash function for HCTR2. + * + * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi> + * Copyright (c) 2009 Intel Corp. + * Author: Huang Ying <ying.huang@intel.com> + * Copyright 2021 Google LLC + */ + +/* + * Code based on crypto/ghash-generic.c + * + * POLYVAL is a keyed hash function similar to GHASH. POLYVAL uses a different + * modulus for finite field multiplication which makes hardware accelerated + * implementations on little-endian machines faster. POLYVAL is used in the + * kernel to implement HCTR2, but was originally specified for AES-GCM-SIV + * (RFC 8452). + * + * For more information see: + * Length-preserving encryption with HCTR2: + * https://eprint.iacr.org/2021/1441.pdf + * AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption: + * https://datatracker.ietf.org/doc/html/rfc8452 + * + * Like GHASH, POLYVAL is not a cryptographic hash function and should + * not be used outside of crypto modes explicitly designed to use POLYVAL. + * + * This implementation uses a convenient trick involving the GHASH and POLYVAL + * fields. This trick allows multiplication in the POLYVAL field to be + * implemented by using multiplication in the GHASH field as a subroutine. An + * element of the POLYVAL field can be converted to an element of the GHASH + * field by computing x*REVERSE(a), where REVERSE reverses the byte-ordering of + * a. Similarly, an element of the GHASH field can be converted back to the + * POLYVAL field by computing REVERSE(x^{-1}*a). For more information, see: + * https://datatracker.ietf.org/doc/html/rfc8452#appendix-A + * + * By using this trick, we do not need to implement the POLYVAL field for the + * generic implementation. + * + * Warning: this generic implementation is not intended to be used in practice + * and is not constant time. For practical use, a hardware accelerated + * implementation of POLYVAL should be used instead. + * + */ + +#include <asm/unaligned.h> +#include <crypto/algapi.h> +#include <crypto/gf128mul.h> +#include <crypto/polyval.h> +#include <crypto/internal/hash.h> +#include <linux/crypto.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/module.h> + +struct polyval_tfm_ctx { + struct gf128mul_4k *gf128; +}; + +struct polyval_desc_ctx { + union { + u8 buffer[POLYVAL_BLOCK_SIZE]; + be128 buffer128; + }; + u32 bytes; +}; + +static void copy_and_reverse(u8 dst[POLYVAL_BLOCK_SIZE], + const u8 src[POLYVAL_BLOCK_SIZE]) +{ + u64 a = get_unaligned((const u64 *)&src[0]); + u64 b = get_unaligned((const u64 *)&src[8]); + + put_unaligned(swab64(a), (u64 *)&dst[8]); + put_unaligned(swab64(b), (u64 *)&dst[0]); +} + +/* + * Performs multiplication in the POLYVAL field using the GHASH field as a + * subroutine. This function is used as a fallback for hardware accelerated + * implementations when simd registers are unavailable. + * + * Note: This function is not used for polyval-generic, instead we use the 4k + * lookup table implementation for finite field multiplication. + */ +void polyval_mul_non4k(u8 *op1, const u8 *op2) +{ + be128 a, b; + + // Assume one argument is in Montgomery form and one is not. + copy_and_reverse((u8 *)&a, op1); + copy_and_reverse((u8 *)&b, op2); + gf128mul_x_lle(&a, &a); + gf128mul_lle(&a, &b); + copy_and_reverse(op1, (u8 *)&a); +} +EXPORT_SYMBOL_GPL(polyval_mul_non4k); + +/* + * Perform a POLYVAL update using non4k multiplication. This function is used + * as a fallback for hardware accelerated implementations when simd registers + * are unavailable. + * + * Note: This function is not used for polyval-generic, instead we use the 4k + * lookup table implementation of finite field multiplication. + */ +void polyval_update_non4k(const u8 *key, const u8 *in, + size_t nblocks, u8 *accumulator) +{ + while (nblocks--) { + crypto_xor(accumulator, in, POLYVAL_BLOCK_SIZE); + polyval_mul_non4k(accumulator, key); + in += POLYVAL_BLOCK_SIZE; + } +} +EXPORT_SYMBOL_GPL(polyval_update_non4k); + +static int polyval_setkey(struct crypto_shash *tfm, + const u8 *key, unsigned int keylen) +{ + struct polyval_tfm_ctx *ctx = crypto_shash_ctx(tfm); + be128 k; + + if (keylen != POLYVAL_BLOCK_SIZE) + return -EINVAL; + + gf128mul_free_4k(ctx->gf128); + + BUILD_BUG_ON(sizeof(k) != POLYVAL_BLOCK_SIZE); + copy_and_reverse((u8 *)&k, key); + gf128mul_x_lle(&k, &k); + + ctx->gf128 = gf128mul_init_4k_lle(&k); + memzero_explicit(&k, POLYVAL_BLOCK_SIZE); + + if (!ctx->gf128) + return -ENOMEM; + + return 0; +} + +static int polyval_init(struct shash_desc *desc) +{ + struct polyval_desc_ctx *dctx = shash_desc_ctx(desc); + + memset(dctx, 0, sizeof(*dctx)); + + return 0; +} + +static int polyval_update(struct shash_desc *desc, + const u8 *src, unsigned int srclen) +{ + struct polyval_desc_ctx *dctx = shash_desc_ctx(desc); + const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm); + u8 *pos; + u8 tmp[POLYVAL_BLOCK_SIZE]; + int n; + + if (dctx->bytes) { + n = min(srclen, dctx->bytes); + pos = dctx->buffer + dctx->bytes - 1; + + dctx->bytes -= n; + srclen -= n; + + while (n--) + *pos-- ^= *src++; + + if (!dctx->bytes) + gf128mul_4k_lle(&dctx->buffer128, ctx->gf128); + } + + while (srclen >= POLYVAL_BLOCK_SIZE) { + copy_and_reverse(tmp, src); + crypto_xor(dctx->buffer, tmp, POLYVAL_BLOCK_SIZE); + gf128mul_4k_lle(&dctx->buffer128, ctx->gf128); + src += POLYVAL_BLOCK_SIZE; + srclen -= POLYVAL_BLOCK_SIZE; + } + + if (srclen) { + dctx->bytes = POLYVAL_BLOCK_SIZE - srclen; + pos = dctx->buffer + POLYVAL_BLOCK_SIZE - 1; + while (srclen--) + *pos-- ^= *src++; + } + + return 0; +} + +static int polyval_final(struct shash_desc *desc, u8 *dst) +{ + struct polyval_desc_ctx *dctx = shash_desc_ctx(desc); + const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm); + + if (dctx->bytes) + gf128mul_4k_lle(&dctx->buffer128, ctx->gf128); + copy_and_reverse(dst, dctx->buffer); + return 0; +} + +static void polyval_exit_tfm(struct crypto_tfm *tfm) +{ + struct polyval_tfm_ctx *ctx = crypto_tfm_ctx(tfm); + + gf128mul_free_4k(ctx->gf128); +} + +static struct shash_alg polyval_alg = { + .digestsize = POLYVAL_DIGEST_SIZE, + .init = polyval_init, + .update = polyval_update, + .final = polyval_final, + .setkey = polyval_setkey, + .descsize = sizeof(struct polyval_desc_ctx), + .base = { + .cra_name = "polyval", + .cra_driver_name = "polyval-generic", + .cra_priority = 100, + .cra_blocksize = POLYVAL_BLOCK_SIZE, + .cra_ctxsize = sizeof(struct polyval_tfm_ctx), + .cra_module = THIS_MODULE, + .cra_exit = polyval_exit_tfm, + }, +}; + +static int __init polyval_mod_init(void) +{ + return crypto_register_shash(&polyval_alg); +} + +static void __exit polyval_mod_exit(void) +{ + crypto_unregister_shash(&polyval_alg); +} + +subsys_initcall(polyval_mod_init); +module_exit(polyval_mod_exit); + +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("POLYVAL hash function"); +MODULE_ALIAS_CRYPTO("polyval"); +MODULE_ALIAS_CRYPTO("polyval-generic"); |