the-tree/crypto/polyval-generic.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * POLYVAL: hash function for HCTR2.
0004  *
0005  * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi>
0006  * Copyright (c) 2009 Intel Corp.
0007  *   Author: Huang Ying <ying.huang@intel.com>
0008  * Copyright 2021 Google LLC
0009  */
0010
0011 /*
0012  * Code based on crypto/ghash-generic.c
0013  *
0014  * POLYVAL is a keyed hash function similar to GHASH. POLYVAL uses a different
0015  * modulus for finite field multiplication which makes hardware accelerated
0016  * implementations on little-endian machines faster. POLYVAL is used in the
0017  * kernel to implement HCTR2, but was originally specified for AES-GCM-SIV
0018  * (RFC 8452).
0019  *
0020  * For more information see:
0021  * Length-preserving encryption with HCTR2:
0022  *   https://eprint.iacr.org/2021/1441.pdf
0023  * AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption:
0024  *   https://datatracker.ietf.org/doc/html/rfc8452
0025  *
0026  * Like GHASH, POLYVAL is not a cryptographic hash function and should
0027  * not be used outside of crypto modes explicitly designed to use POLYVAL.
0028  *
0029  * This implementation uses a convenient trick involving the GHASH and POLYVAL
0030  * fields. This trick allows multiplication in the POLYVAL field to be
0031  * implemented by using multiplication in the GHASH field as a subroutine. An
0032  * element of the POLYVAL field can be converted to an element of the GHASH
0033  * field by computing x*REVERSE(a), where REVERSE reverses the byte-ordering of
0034  * a. Similarly, an element of the GHASH field can be converted back to the
0035  * POLYVAL field by computing REVERSE(x^{-1}*a). For more information, see:
0036  * https://datatracker.ietf.org/doc/html/rfc8452#appendix-A
0037  *
0038  * By using this trick, we do not need to implement the POLYVAL field for the
0039  * generic implementation.
0040  *
0041  * Warning: this generic implementation is not intended to be used in practice
0042  * and is not constant time. For practical use, a hardware accelerated
0043  * implementation of POLYVAL should be used instead.
0044  *
0045  */
0046
0047 #include <asm/unaligned.h>
0048 #include <crypto/algapi.h>
0049 #include <crypto/gf128mul.h>
0050 #include <crypto/polyval.h>
0051 #include <crypto/internal/hash.h>
0052 #include <linux/crypto.h>
0053 #include <linux/init.h>
0054 #include <linux/kernel.h>
0055 #include <linux/module.h>
0056
0057 struct polyval_tfm_ctx {
0058     struct gf128mul_4k *gf128;
0059 };
0060
0061 struct polyval_desc_ctx {
0062     union {
0063         u8 buffer[POLYVAL_BLOCK_SIZE];
0064         be128 buffer128;
0065     };
0066     u32 bytes;
0067 };
0068
0069 static void copy_and_reverse(u8 dst[POLYVAL_BLOCK_SIZE],
0070                  const u8 src[POLYVAL_BLOCK_SIZE])
0071 {
0072     u64 a = get_unaligned((const u64 *)&src[0]);
0073     u64 b = get_unaligned((const u64 *)&src[8]);
0074
0075     put_unaligned(swab64(a), (u64 *)&dst[8]);
0076     put_unaligned(swab64(b), (u64 *)&dst[0]);
0077 }
0078
0079 /*
0080  * Performs multiplication in the POLYVAL field using the GHASH field as a
0081  * subroutine.  This function is used as a fallback for hardware accelerated
0082  * implementations when simd registers are unavailable.
0083  *
0084  * Note: This function is not used for polyval-generic, instead we use the 4k
0085  * lookup table implementation for finite field multiplication.
0086  */
0087 void polyval_mul_non4k(u8 *op1, const u8 *op2)
0088 {
0089     be128 a, b;
0090
0091     // Assume one argument is in Montgomery form and one is not.
0092     copy_and_reverse((u8 *)&a, op1);
0093     copy_and_reverse((u8 *)&b, op2);
0094     gf128mul_x_lle(&a, &a);
0095     gf128mul_lle(&a, &b);
0096     copy_and_reverse(op1, (u8 *)&a);
0097 }
0098 EXPORT_SYMBOL_GPL(polyval_mul_non4k);
0099
0100 /*
0101  * Perform a POLYVAL update using non4k multiplication.  This function is used
0102  * as a fallback for hardware accelerated implementations when simd registers
0103  * are unavailable.
0104  *
0105  * Note: This function is not used for polyval-generic, instead we use the 4k
0106  * lookup table implementation of finite field multiplication.
0107  */
0108 void polyval_update_non4k(const u8 *key, const u8 *in,
0109               size_t nblocks, u8 *accumulator)
0110 {
0111     while (nblocks--) {
0112         crypto_xor(accumulator, in, POLYVAL_BLOCK_SIZE);
0113         polyval_mul_non4k(accumulator, key);
0114         in += POLYVAL_BLOCK_SIZE;
0115     }
0116 }
0117 EXPORT_SYMBOL_GPL(polyval_update_non4k);
0118
0119 static int polyval_setkey(struct crypto_shash *tfm,
0120               const u8 *key, unsigned int keylen)
0121 {
0122     struct polyval_tfm_ctx *ctx = crypto_shash_ctx(tfm);
0123     be128 k;
0124
0125     if (keylen != POLYVAL_BLOCK_SIZE)
0126         return -EINVAL;
0127
0128     gf128mul_free_4k(ctx->gf128);
0129
0130     BUILD_BUG_ON(sizeof(k) != POLYVAL_BLOCK_SIZE);
0131     copy_and_reverse((u8 *)&k, key);
0132     gf128mul_x_lle(&k, &k);
0133
0134     ctx->gf128 = gf128mul_init_4k_lle(&k);
0135     memzero_explicit(&k, POLYVAL_BLOCK_SIZE);
0136
0137     if (!ctx->gf128)
0138         return -ENOMEM;
0139
0140     return 0;
0141 }
0142
0143 static int polyval_init(struct shash_desc *desc)
0144 {
0145     struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
0146
0147     memset(dctx, 0, sizeof(*dctx));
0148
0149     return 0;
0150 }
0151
0152 static int polyval_update(struct shash_desc *desc,
0153              const u8 *src, unsigned int srclen)
0154 {
0155     struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
0156     const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm);
0157     u8 *pos;
0158     u8 tmp[POLYVAL_BLOCK_SIZE];
0159     int n;
0160
0161     if (dctx->bytes) {
0162         n = min(srclen, dctx->bytes);
0163         pos = dctx->buffer + dctx->bytes - 1;
0164
0165         dctx->bytes -= n;
0166         srclen -= n;
0167
0168         while (n--)
0169             *pos-- ^= *src++;
0170
0171         if (!dctx->bytes)
0172             gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
0173     }
0174
0175     while (srclen >= POLYVAL_BLOCK_SIZE) {
0176         copy_and_reverse(tmp, src);
0177         crypto_xor(dctx->buffer, tmp, POLYVAL_BLOCK_SIZE);
0178         gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
0179         src += POLYVAL_BLOCK_SIZE;
0180         srclen -= POLYVAL_BLOCK_SIZE;
0181     }
0182
0183     if (srclen) {
0184         dctx->bytes = POLYVAL_BLOCK_SIZE - srclen;
0185         pos = dctx->buffer + POLYVAL_BLOCK_SIZE - 1;
0186         while (srclen--)
0187             *pos-- ^= *src++;
0188     }
0189
0190     return 0;
0191 }
0192
0193 static int polyval_final(struct shash_desc *desc, u8 *dst)
0194 {
0195     struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
0196     const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm);
0197
0198     if (dctx->bytes)
0199         gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
0200     copy_and_reverse(dst, dctx->buffer);
0201     return 0;
0202 }
0203
0204 static void polyval_exit_tfm(struct crypto_tfm *tfm)
0205 {
0206     struct polyval_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
0207
0208     gf128mul_free_4k(ctx->gf128);
0209 }
0210
0211 static struct shash_alg polyval_alg = {
0212     .digestsize = POLYVAL_DIGEST_SIZE,
0213     .init       = polyval_init,
0214     .update     = polyval_update,
0215     .final      = polyval_final,
0216     .setkey     = polyval_setkey,
0217     .descsize   = sizeof(struct polyval_desc_ctx),
0218     .base       = {
0219         .cra_name       = "polyval",
0220         .cra_driver_name    = "polyval-generic",
0221         .cra_priority       = 100,
0222         .cra_blocksize      = POLYVAL_BLOCK_SIZE,
0223         .cra_ctxsize        = sizeof(struct polyval_tfm_ctx),
0224         .cra_module     = THIS_MODULE,
0225         .cra_exit       = polyval_exit_tfm,
0226     },
0227 };
0228
0229 static int __init polyval_mod_init(void)
0230 {
0231     return crypto_register_shash(&polyval_alg);
0232 }
0233
0234 static void __exit polyval_mod_exit(void)
0235 {
0236     crypto_unregister_shash(&polyval_alg);
0237 }
0238
0239 subsys_initcall(polyval_mod_init);
0240 module_exit(polyval_mod_exit);
0241
0242 MODULE_LICENSE("GPL");
0243 MODULE_DESCRIPTION("POLYVAL hash function");
0244 MODULE_ALIAS_CRYPTO("polyval");
0245 MODULE_ALIAS_CRYPTO("polyval-generic");