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