-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
- * Common values for the Polyval hash algorithm
+ * POLYVAL library API
*
- * Copyright 2021 Google LLC
+ * Copyright 2025 Google LLC
*/
#ifndef _CRYPTO_POLYVAL_H
#define _CRYPTO_POLYVAL_H
+#include <linux/string.h>
+#include <linux/types.h>
+
#define POLYVAL_BLOCK_SIZE 16
#define POLYVAL_DIGEST_SIZE 16
+/**
+ * struct polyval_elem - An element of the POLYVAL finite field
+ * @bytes: View of the element as a byte array (unioned with @lo and @hi)
+ * @lo: The low 64 terms of the element's polynomial
+ * @hi: The high 64 terms of the element's polynomial
+ *
+ * This represents an element of the finite field GF(2^128), using the POLYVAL
+ * convention: little-endian byte order and natural bit order.
+ */
+struct polyval_elem {
+ union {
+ u8 bytes[POLYVAL_BLOCK_SIZE];
+ struct {
+ __le64 lo;
+ __le64 hi;
+ };
+ };
+};
+
+/**
+ * struct polyval_key - Prepared key for POLYVAL
+ *
+ * This may contain just the raw key H, or it may contain precomputed key
+ * powers, depending on the platform's POLYVAL implementation. Use
+ * polyval_preparekey() to initialize this.
+ */
+struct polyval_key {
+#ifdef CONFIG_CRYPTO_LIB_POLYVAL_ARCH
+#error "Unhandled arch"
+#else /* CONFIG_CRYPTO_LIB_POLYVAL_ARCH */
+ /** @h: The hash key H */
+ struct polyval_elem h;
+#endif /* !CONFIG_CRYPTO_LIB_POLYVAL_ARCH */
+};
+
+/**
+ * struct polyval_ctx - Context for computing a POLYVAL value
+ * @key: Pointer to the prepared POLYVAL key. The user of the API is
+ * responsible for ensuring that the key lives as long as the context.
+ * @acc: The accumulator
+ * @partial: Number of data bytes processed so far modulo POLYVAL_BLOCK_SIZE
+ */
+struct polyval_ctx {
+ const struct polyval_key *key;
+ struct polyval_elem acc;
+ size_t partial;
+};
+
+/**
+ * polyval_preparekey() - Prepare a POLYVAL key
+ * @key: (output) The key structure to initialize
+ * @raw_key: The raw hash key
+ *
+ * Initialize a POLYVAL key structure from a raw key. This may be a simple
+ * copy, or it may involve precomputing powers of the key, depending on the
+ * platform's POLYVAL implementation.
+ *
+ * Context: Any context.
+ */
+#ifdef CONFIG_CRYPTO_LIB_POLYVAL_ARCH
+void polyval_preparekey(struct polyval_key *key,
+ const u8 raw_key[POLYVAL_BLOCK_SIZE]);
+
+#else
+static inline void polyval_preparekey(struct polyval_key *key,
+ const u8 raw_key[POLYVAL_BLOCK_SIZE])
+{
+ /* Just a simple copy, so inline it. */
+ memcpy(key->h.bytes, raw_key, POLYVAL_BLOCK_SIZE);
+}
#endif
+
+/**
+ * polyval_init() - Initialize a POLYVAL context for a new message
+ * @ctx: The context to initialize
+ * @key: The key to use. Note that a pointer to the key is saved in the
+ * context, so the key must live at least as long as the context.
+ */
+static inline void polyval_init(struct polyval_ctx *ctx,
+ const struct polyval_key *key)
+{
+ *ctx = (struct polyval_ctx){ .key = key };
+}
+
+/**
+ * polyval_import_blkaligned() - Import a POLYVAL accumulator value
+ * @ctx: The context to initialize
+ * @key: The key to import. Note that a pointer to the key is saved in the
+ * context, so the key must live at least as long as the context.
+ * @acc: The accumulator value to import.
+ *
+ * This imports an accumulator that was saved by polyval_export_blkaligned().
+ * The same key must be used.
+ */
+static inline void
+polyval_import_blkaligned(struct polyval_ctx *ctx,
+ const struct polyval_key *key,
+ const struct polyval_elem *acc)
+{
+ *ctx = (struct polyval_ctx){ .key = key, .acc = *acc };
+}
+
+/**
+ * polyval_export_blkaligned() - Export a POLYVAL accumulator value
+ * @ctx: The context to export the accumulator value from
+ * @acc: (output) The exported accumulator value
+ *
+ * This exports the accumulator from a POLYVAL context. The number of data
+ * bytes processed so far must be a multiple of POLYVAL_BLOCK_SIZE.
+ */
+static inline void polyval_export_blkaligned(const struct polyval_ctx *ctx,
+ struct polyval_elem *acc)
+{
+ *acc = ctx->acc;
+}
+
+/**
+ * polyval_update() - Update a POLYVAL context with message data
+ * @ctx: The context to update; must have been initialized
+ * @data: The message data
+ * @len: The data length in bytes. Doesn't need to be block-aligned.
+ *
+ * This can be called any number of times.
+ *
+ * Context: Any context.
+ */
+void polyval_update(struct polyval_ctx *ctx, const u8 *data, size_t len);
+
+/**
+ * polyval_final() - Finish computing a POLYVAL value
+ * @ctx: The context to finalize
+ * @out: The output value
+ *
+ * If the total data length isn't a multiple of POLYVAL_BLOCK_SIZE, then the
+ * final block is automatically zero-padded.
+ *
+ * After finishing, this zeroizes @ctx. So the caller does not need to do it.
+ *
+ * Context: Any context.
+ */
+void polyval_final(struct polyval_ctx *ctx, u8 out[POLYVAL_BLOCK_SIZE]);
+
+/**
+ * polyval() - Compute a POLYVAL value
+ * @key: The prepared key
+ * @data: The message data
+ * @len: The data length in bytes. Doesn't need to be block-aligned.
+ * @out: The output value
+ *
+ * Context: Any context.
+ */
+static inline void polyval(const struct polyval_key *key,
+ const u8 *data, size_t len,
+ u8 out[POLYVAL_BLOCK_SIZE])
+{
+ struct polyval_ctx ctx;
+
+ polyval_init(&ctx, key);
+ polyval_update(&ctx, data, len);
+ polyval_final(&ctx, out);
+}
+
+#endif /* _CRYPTO_POLYVAL_H */
--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * POLYVAL library functions
+ *
+ * Copyright 2025 Google LLC
+ */
+
+#include <crypto/polyval.h>
+#include <linux/export.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/unaligned.h>
+
+/*
+ * POLYVAL is an almost-XOR-universal hash function. Similar to GHASH, POLYVAL
+ * interprets the message as the coefficients of a polynomial in GF(2^128) and
+ * evaluates that polynomial at a secret point. POLYVAL has a simple
+ * mathematical relationship with GHASH, but it uses a better field convention
+ * which makes it easier and faster to implement.
+ *
+ * POLYVAL is not a cryptographic hash function, and it should be used only by
+ * algorithms that are specifically designed to use it.
+ *
+ * POLYVAL is specified by "AES-GCM-SIV: Nonce Misuse-Resistant Authenticated
+ * Encryption" (https://datatracker.ietf.org/doc/html/rfc8452)
+ *
+ * POLYVAL is also used by HCTR2. See "Length-preserving encryption with HCTR2"
+ * (https://eprint.iacr.org/2021/1441.pdf).
+ *
+ * This file provides a library API for POLYVAL. This API can delegate to
+ * either a generic implementation or an architecture-optimized implementation.
+ *
+ * For the generic implementation, we don't use the traditional table approach
+ * to GF(2^128) multiplication. That approach is not constant-time and requires
+ * a lot of memory. Instead, we use a different approach which emulates
+ * carryless multiplication using standard multiplications by spreading the data
+ * bits apart using "holes". This allows the carries to spill harmlessly. This
+ * approach is borrowed from BoringSSL, which in turn credits BearSSL's
+ * documentation (https://bearssl.org/constanttime.html#ghash-for-gcm) for the
+ * "holes" trick and a presentation by Shay Gueron
+ * (https://crypto.stanford.edu/RealWorldCrypto/slides/gueron.pdf) for the
+ * 256-bit => 128-bit reduction algorithm.
+ */
+
+#ifdef CONFIG_ARCH_SUPPORTS_INT128
+
+/* Do a 64 x 64 => 128 bit carryless multiplication. */
+static void clmul64(u64 a, u64 b, u64 *out_lo, u64 *out_hi)
+{
+ /*
+ * With 64-bit multiplicands and one term every 4 bits, there would be
+ * up to 64 / 4 = 16 one bits per column when each multiplication is
+ * written out as a series of additions in the schoolbook manner.
+ * Unfortunately, that doesn't work since the value 16 is 1 too large to
+ * fit in 4 bits. Carries would sometimes overflow into the next term.
+ *
+ * Using one term every 5 bits would work. However, that would cost
+ * 5 x 5 = 25 multiplications instead of 4 x 4 = 16.
+ *
+ * Instead, mask off 4 bits from one multiplicand, giving a max of 15
+ * one bits per column. Then handle those 4 bits separately.
+ */
+ u64 a0 = a & 0x1111111111111110;
+ u64 a1 = a & 0x2222222222222220;
+ u64 a2 = a & 0x4444444444444440;
+ u64 a3 = a & 0x8888888888888880;
+
+ u64 b0 = b & 0x1111111111111111;
+ u64 b1 = b & 0x2222222222222222;
+ u64 b2 = b & 0x4444444444444444;
+ u64 b3 = b & 0x8888888888888888;
+
+ /* Multiply the high 60 bits of @a by @b. */
+ u128 c0 = (a0 * (u128)b0) ^ (a1 * (u128)b3) ^
+ (a2 * (u128)b2) ^ (a3 * (u128)b1);
+ u128 c1 = (a0 * (u128)b1) ^ (a1 * (u128)b0) ^
+ (a2 * (u128)b3) ^ (a3 * (u128)b2);
+ u128 c2 = (a0 * (u128)b2) ^ (a1 * (u128)b1) ^
+ (a2 * (u128)b0) ^ (a3 * (u128)b3);
+ u128 c3 = (a0 * (u128)b3) ^ (a1 * (u128)b2) ^
+ (a2 * (u128)b1) ^ (a3 * (u128)b0);
+
+ /* Multiply the low 4 bits of @a by @b. */
+ u64 e0 = -(a & 1) & b;
+ u64 e1 = -((a >> 1) & 1) & b;
+ u64 e2 = -((a >> 2) & 1) & b;
+ u64 e3 = -((a >> 3) & 1) & b;
+ u64 extra_lo = e0 ^ (e1 << 1) ^ (e2 << 2) ^ (e3 << 3);
+ u64 extra_hi = (e1 >> 63) ^ (e2 >> 62) ^ (e3 >> 61);
+
+ /* Add all the intermediate products together. */
+ *out_lo = (((u64)c0) & 0x1111111111111111) ^
+ (((u64)c1) & 0x2222222222222222) ^
+ (((u64)c2) & 0x4444444444444444) ^
+ (((u64)c3) & 0x8888888888888888) ^ extra_lo;
+ *out_hi = (((u64)(c0 >> 64)) & 0x1111111111111111) ^
+ (((u64)(c1 >> 64)) & 0x2222222222222222) ^
+ (((u64)(c2 >> 64)) & 0x4444444444444444) ^
+ (((u64)(c3 >> 64)) & 0x8888888888888888) ^ extra_hi;
+}
+
+#else /* CONFIG_ARCH_SUPPORTS_INT128 */
+
+/* Do a 32 x 32 => 64 bit carryless multiplication. */
+static u64 clmul32(u32 a, u32 b)
+{
+ /*
+ * With 32-bit multiplicands and one term every 4 bits, there are up to
+ * 32 / 4 = 8 one bits per column when each multiplication is written
+ * out as a series of additions in the schoolbook manner. The value 8
+ * fits in 4 bits, so the carries don't overflow into the next term.
+ */
+ u32 a0 = a & 0x11111111;
+ u32 a1 = a & 0x22222222;
+ u32 a2 = a & 0x44444444;
+ u32 a3 = a & 0x88888888;
+
+ u32 b0 = b & 0x11111111;
+ u32 b1 = b & 0x22222222;
+ u32 b2 = b & 0x44444444;
+ u32 b3 = b & 0x88888888;
+
+ u64 c0 = (a0 * (u64)b0) ^ (a1 * (u64)b3) ^
+ (a2 * (u64)b2) ^ (a3 * (u64)b1);
+ u64 c1 = (a0 * (u64)b1) ^ (a1 * (u64)b0) ^
+ (a2 * (u64)b3) ^ (a3 * (u64)b2);
+ u64 c2 = (a0 * (u64)b2) ^ (a1 * (u64)b1) ^
+ (a2 * (u64)b0) ^ (a3 * (u64)b3);
+ u64 c3 = (a0 * (u64)b3) ^ (a1 * (u64)b2) ^
+ (a2 * (u64)b1) ^ (a3 * (u64)b0);
+
+ /* Add all the intermediate products together. */
+ return (c0 & 0x1111111111111111) ^
+ (c1 & 0x2222222222222222) ^
+ (c2 & 0x4444444444444444) ^
+ (c3 & 0x8888888888888888);
+}
+
+/* Do a 64 x 64 => 128 bit carryless multiplication. */
+static void clmul64(u64 a, u64 b, u64 *out_lo, u64 *out_hi)
+{
+ u32 a_lo = (u32)a;
+ u32 a_hi = a >> 32;
+ u32 b_lo = (u32)b;
+ u32 b_hi = b >> 32;
+
+ /* Karatsuba multiplication */
+ u64 lo = clmul32(a_lo, b_lo);
+ u64 hi = clmul32(a_hi, b_hi);
+ u64 mi = clmul32(a_lo ^ a_hi, b_lo ^ b_hi) ^ lo ^ hi;
+
+ *out_lo = lo ^ (mi << 32);
+ *out_hi = hi ^ (mi >> 32);
+}
+#endif /* !CONFIG_ARCH_SUPPORTS_INT128 */
+
+/* Compute @a = @a * @b * x^-128 in the POLYVAL field. */
+static void __maybe_unused
+polyval_mul_generic(struct polyval_elem *a, const struct polyval_elem *b)
+{
+ u64 c0, c1, c2, c3, mi0, mi1;
+
+ /*
+ * Carryless-multiply @a by @b using Karatsuba multiplication. Store
+ * the 256-bit product in @c0 (low) through @c3 (high).
+ */
+ clmul64(le64_to_cpu(a->lo), le64_to_cpu(b->lo), &c0, &c1);
+ clmul64(le64_to_cpu(a->hi), le64_to_cpu(b->hi), &c2, &c3);
+ clmul64(le64_to_cpu(a->lo ^ a->hi), le64_to_cpu(b->lo ^ b->hi),
+ &mi0, &mi1);
+ mi0 ^= c0 ^ c2;
+ mi1 ^= c1 ^ c3;
+ c1 ^= mi0;
+ c2 ^= mi1;
+
+ /*
+ * Cancel out the low 128 bits of the product by adding multiples of
+ * G(x) = x^128 + x^127 + x^126 + x^121 + 1. Do this in two steps, each
+ * of which cancels out 64 bits. Note that we break G(x) into three
+ * parts: 1, x^64 * (x^63 + x^62 + x^57), and x^128 * 1.
+ */
+
+ /*
+ * First, add G(x) times c0 as follows:
+ *
+ * (c0, c1, c2) = (0,
+ * c1 + (c0 * (x^63 + x^62 + x^57) mod x^64),
+ * c2 + c0 + floor((c0 * (x^63 + x^62 + x^57)) / x^64))
+ */
+ c1 ^= (c0 << 63) ^ (c0 << 62) ^ (c0 << 57);
+ c2 ^= c0 ^ (c0 >> 1) ^ (c0 >> 2) ^ (c0 >> 7);
+
+ /*
+ * Second, add G(x) times the new c1:
+ *
+ * (c1, c2, c3) = (0,
+ * c2 + (c1 * (x^63 + x^62 + x^57) mod x^64),
+ * c3 + c1 + floor((c1 * (x^63 + x^62 + x^57)) / x^64))
+ */
+ c2 ^= (c1 << 63) ^ (c1 << 62) ^ (c1 << 57);
+ c3 ^= c1 ^ (c1 >> 1) ^ (c1 >> 2) ^ (c1 >> 7);
+
+ /* Return (c2, c3). This implicitly multiplies by x^-128. */
+ a->lo = cpu_to_le64(c2);
+ a->hi = cpu_to_le64(c3);
+}
+
+static void __maybe_unused
+polyval_blocks_generic(struct polyval_elem *acc, const struct polyval_elem *key,
+ const u8 *data, size_t nblocks)
+{
+ do {
+ acc->lo ^= get_unaligned((__le64 *)data);
+ acc->hi ^= get_unaligned((__le64 *)(data + 8));
+ polyval_mul_generic(acc, key);
+ data += POLYVAL_BLOCK_SIZE;
+ } while (--nblocks);
+}
+
+/* Include the arch-optimized implementation of POLYVAL, if one is available. */
+#ifdef CONFIG_CRYPTO_LIB_POLYVAL_ARCH
+#include "polyval.h" /* $(SRCARCH)/polyval.h */
+void polyval_preparekey(struct polyval_key *key,
+ const u8 raw_key[POLYVAL_BLOCK_SIZE])
+{
+ polyval_preparekey_arch(key, raw_key);
+}
+EXPORT_SYMBOL_GPL(polyval_preparekey);
+#endif /* Else, polyval_preparekey() is an inline function. */
+
+/*
+ * polyval_mul_generic() and polyval_blocks_generic() take the key as a
+ * polyval_elem rather than a polyval_key, so that arch-optimized
+ * implementations with a different key format can use it as a fallback (if they
+ * have H^1 stored somewhere in their struct). Thus, the following dispatch
+ * code is needed to pass the appropriate key argument.
+ */
+
+static void polyval_mul(struct polyval_ctx *ctx)
+{
+#ifdef CONFIG_CRYPTO_LIB_POLYVAL_ARCH
+ polyval_mul_arch(&ctx->acc, ctx->key);
+#else
+ polyval_mul_generic(&ctx->acc, &ctx->key->h);
+#endif
+}
+
+static void polyval_blocks(struct polyval_ctx *ctx,
+ const u8 *data, size_t nblocks)
+{
+#ifdef CONFIG_CRYPTO_LIB_POLYVAL_ARCH
+ polyval_blocks_arch(&ctx->acc, ctx->key, data, nblocks);
+#else
+ polyval_blocks_generic(&ctx->acc, &ctx->key->h, data, nblocks);
+#endif
+}
+
+void polyval_update(struct polyval_ctx *ctx, const u8 *data, size_t len)
+{
+ if (unlikely(ctx->partial)) {
+ size_t n = min(len, POLYVAL_BLOCK_SIZE - ctx->partial);
+
+ len -= n;
+ while (n--)
+ ctx->acc.bytes[ctx->partial++] ^= *data++;
+ if (ctx->partial < POLYVAL_BLOCK_SIZE)
+ return;
+ polyval_mul(ctx);
+ }
+ if (len >= POLYVAL_BLOCK_SIZE) {
+ size_t nblocks = len / POLYVAL_BLOCK_SIZE;
+
+ polyval_blocks(ctx, data, nblocks);
+ data += len & ~(POLYVAL_BLOCK_SIZE - 1);
+ len &= POLYVAL_BLOCK_SIZE - 1;
+ }
+ for (size_t i = 0; i < len; i++)
+ ctx->acc.bytes[i] ^= data[i];
+ ctx->partial = len;
+}
+EXPORT_SYMBOL_GPL(polyval_update);
+
+void polyval_final(struct polyval_ctx *ctx, u8 out[POLYVAL_BLOCK_SIZE])
+{
+ if (unlikely(ctx->partial))
+ polyval_mul(ctx);
+ memcpy(out, &ctx->acc, POLYVAL_BLOCK_SIZE);
+ memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL_GPL(polyval_final);
+
+#ifdef polyval_mod_init_arch
+static int __init polyval_mod_init(void)
+{
+ polyval_mod_init_arch();
+ return 0;
+}
+subsys_initcall(polyval_mod_init);
+
+static void __exit polyval_mod_exit(void)
+{
+}
+module_exit(polyval_mod_exit);
+#endif
+
+MODULE_DESCRIPTION("POLYVAL almost-XOR-universal hash function");
+MODULE_LICENSE("GPL");
projects / thirdparty / kernel / linux.git / commitdiff
