linux/crypto/nhpoly1305.c

// SPDX-License-Identifier: GPL-2.0
/*
 * NHPoly1305 - ε-almost-∆-universal hash function for Adiantum
 *
 * Copyright 2018 Google LLC
 */

/*
 * "NHPoly1305" is the main component of Adiantum hashing.
 * Specifically, it is the calculation
 *
 *	H_L ← Poly1305_{K_L}(NH_{K_N}(pad_{128}(L)))
 *
 * from the procedure in section 6.4 of the Adiantum paper [1].  It is an
 * ε-almost-∆-universal (ε-∆U) hash function for equal-length inputs over
 * Z/(2^{128}Z), where the "∆" operation is addition.  It hashes 1024-byte
 * chunks of the input with the NH hash function [2], reducing the input length
 * by 32x.  The resulting NH digests are evaluated as a polynomial in
 * GF(2^{130}-5), like in the Poly1305 MAC [3].  Note that the polynomial
 * evaluation by itself would suffice to achieve the ε-∆U property; NH is used
 * for performance since it's over twice as fast as Poly1305.
 *
 * This is *not* a cryptographic hash function; do not use it as such!
 *
 * [1] Adiantum: length-preserving encryption for entry-level processors
 *     (https://eprint.iacr.org/2018/720.pdf)
 * [2] UMAC: Fast and Secure Message Authentication
 *     (https://fastcrypto.org/umac/umac_proc.pdf)
 * [3] The Poly1305-AES message-authentication code
 *     (https://cr.yp.to/mac/poly1305-20050329.pdf)
 */

#include <asm/unaligned.h>
#include <crypto/algapi.h>
#include <crypto/internal/hash.h>
#include <crypto/internal/poly1305.h>
#include <crypto/nhpoly1305.h>
#include <linux/crypto.h>
#include <linux/kernel.h>
#include <linux/module.h>

static void nh_generic(const u32 *key, const u8 *message, size_t message_len,
		       __le64 hash[NH_NUM_PASSES])
{ … }

/* Pass the next NH hash value through Poly1305 */
static void process_nh_hash_value(struct nhpoly1305_state *state,
				  const struct nhpoly1305_key *key)
{ … }

/*
 * Feed the next portion of the source data, as a whole number of 16-byte
 * "NH message units", through NH and Poly1305.  Each NH hash is taken over
 * 1024 bytes, except possibly the final one which is taken over a multiple of
 * 16 bytes up to 1024.  Also, in the case where data is passed in misaligned
 * chunks, we combine partial hashes; the end result is the same either way.
 */
static void nhpoly1305_units(struct nhpoly1305_state *state,
			     const struct nhpoly1305_key *key,
			     const u8 *src, unsigned int srclen, nh_t nh_fn)
{ … }

int crypto_nhpoly1305_setkey(struct crypto_shash *tfm,
			     const u8 *key, unsigned int keylen)
{ … }
EXPORT_SYMBOL(…);

int crypto_nhpoly1305_init(struct shash_desc *desc)
{ … }
EXPORT_SYMBOL(…);

int crypto_nhpoly1305_update_helper(struct shash_desc *desc,
				    const u8 *src, unsigned int srclen,
				    nh_t nh_fn)
{ … }
EXPORT_SYMBOL(…);

int crypto_nhpoly1305_update(struct shash_desc *desc,
			     const u8 *src, unsigned int srclen)
{ … }
EXPORT_SYMBOL(…);

int crypto_nhpoly1305_final_helper(struct shash_desc *desc, u8 *dst, nh_t nh_fn)
{ … }
EXPORT_SYMBOL(…);

int crypto_nhpoly1305_final(struct shash_desc *desc, u8 *dst)
{ … }
EXPORT_SYMBOL(…);

static struct shash_alg nhpoly1305_alg = …;

static int __init nhpoly1305_mod_init(void)
{ … }

static void __exit nhpoly1305_mod_exit(void)
{ … }

subsys_initcall(nhpoly1305_mod_init);
module_exit(nhpoly1305_mod_exit);

MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;
MODULE_AUTHOR(…) …;
MODULE_ALIAS_CRYPTO(…) …;
MODULE_ALIAS_CRYPTO(…) …;