summaryrefslogtreecommitdiff
path: root/crypto/polyval-generic.c
diff options
context:
space:
mode:
Diffstat (limited to 'crypto/polyval-generic.c')
-rw-r--r--crypto/polyval-generic.c205
1 files changed, 205 insertions, 0 deletions
diff --git a/crypto/polyval-generic.c b/crypto/polyval-generic.c
new file mode 100644
index 000000000000..bf2b03b7bfc0
--- /dev/null
+++ b/crypto/polyval-generic.c
@@ -0,0 +1,205 @@
+// 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]);
+}
+
+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");