crypto: polyval - Add POLYVAL support

Add support for POLYVAL, an ε-Δ-universal hash function similar to
GHASH.  This patch only uses POLYVAL as a component to implement HCTR2
mode.  It should be noted that POLYVAL was originally specified for use
in AES-GCM-SIV (RFC 8452), but the kernel does not currently support
this mode.

POLYVAL is implemented as an shash algorithm.  The implementation is
modified from ghash-generic.c.

For more information on POLYVAL 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

Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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");