// SPDX-License-Identifier: GPL-2.0-only

  /*

   * GHASH: hash function for GCM (Galois/Counter Mode).

   *
   * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi>
   * Copyright (c) 2009 Intel Corp.
   *   Author: Huang Ying <ying.huang@intel.com>

   */
  
  /*
   * GHASH is a keyed hash function used in GCM authentication tag generation.
   *
   * The original GCM paper [1] presents GHASH as a function GHASH(H, A, C) which
   * takes a 16-byte hash key H, additional authenticated data A, and a ciphertext
   * C.  It formats A and C into a single byte string X, interprets X as a
   * polynomial over GF(2^128), and evaluates this polynomial at the point H.
   *
   * However, the NIST standard for GCM [2] presents GHASH as GHASH(H, X) where X
   * is the already-formatted byte string containing both A and C.
   *
   * "ghash" in the Linux crypto API uses the 'X' (pre-formatted) convention,
   * since the API supports only a single data stream per hash.  Thus, the
   * formatting of 'A' and 'C' is done in the "gcm" template, not in "ghash".
   *
   * The reason "ghash" is separate from "gcm" is to allow "gcm" to use an
   * accelerated "ghash" when a standalone accelerated "gcm(aes)" is unavailable.
   * It is generally inappropriate to use "ghash" for other purposes, since it is
   * an "ε-almost-XOR-universal hash function", not a cryptographic hash function.
   * It can only be used securely in crypto modes specially designed to use it.

   *

   * [1] The Galois/Counter Mode of Operation (GCM)
   *     (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.694.695&rep=rep1&type=pdf)
   * [2] Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC
   *     (https://csrc.nist.gov/publications/detail/sp/800-38d/final)

   */
  
  #include <crypto/algapi.h>
  #include <crypto/gf128mul.h>

  #include <crypto/ghash.h>

  #include <crypto/internal/hash.h>
  #include <linux/crypto.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/module.h>

  static int ghash_init(struct shash_desc *desc)
  {
  	struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
  
  	memset(dctx, 0, sizeof(*dctx));
  
  	return 0;
  }
  
  static int ghash_setkey(struct crypto_shash *tfm,
  			const u8 *key, unsigned int keylen)
  {
  	struct ghash_ctx *ctx = crypto_shash_ctx(tfm);

  	be128 k;

  	if (keylen != GHASH_BLOCK_SIZE)

  		return -EINVAL;

  
  	if (ctx->gf128)
  		gf128mul_free_4k(ctx->gf128);

  
  	BUILD_BUG_ON(sizeof(k) != GHASH_BLOCK_SIZE);
  	memcpy(&k, key, GHASH_BLOCK_SIZE); /* avoid violating alignment rules */
  	ctx->gf128 = gf128mul_init_4k_lle(&k);
  	memzero_explicit(&k, GHASH_BLOCK_SIZE);

  	if (!ctx->gf128)
  		return -ENOMEM;
  
  	return 0;
  }
  
  static int ghash_update(struct shash_desc *desc,
  			 const u8 *src, unsigned int srclen)
  {
  	struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
  	struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
  	u8 *dst = dctx->buffer;
  
  	if (dctx->bytes) {
  		int n = min(srclen, dctx->bytes);
  		u8 *pos = dst + (GHASH_BLOCK_SIZE - dctx->bytes);
  
  		dctx->bytes -= n;
  		srclen -= n;
  
  		while (n--)
  			*pos++ ^= *src++;
  
  		if (!dctx->bytes)
  			gf128mul_4k_lle((be128 *)dst, ctx->gf128);
  	}
  
  	while (srclen >= GHASH_BLOCK_SIZE) {
  		crypto_xor(dst, src, GHASH_BLOCK_SIZE);
  		gf128mul_4k_lle((be128 *)dst, ctx->gf128);
  		src += GHASH_BLOCK_SIZE;
  		srclen -= GHASH_BLOCK_SIZE;
  	}
  
  	if (srclen) {
  		dctx->bytes = GHASH_BLOCK_SIZE - srclen;
  		while (srclen--)
  			*dst++ ^= *src++;
  	}
  
  	return 0;
  }
  
  static void ghash_flush(struct ghash_ctx *ctx, struct ghash_desc_ctx *dctx)
  {
  	u8 *dst = dctx->buffer;
  
  	if (dctx->bytes) {
  		u8 *tmp = dst + (GHASH_BLOCK_SIZE - dctx->bytes);
  
  		while (dctx->bytes--)
  			*tmp++ ^= 0;
  
  		gf128mul_4k_lle((be128 *)dst, ctx->gf128);
  	}
  
  	dctx->bytes = 0;
  }
  
  static int ghash_final(struct shash_desc *desc, u8 *dst)
  {
  	struct ghash_desc_ctx *dctx = shash_desc_ctx(desc);
  	struct ghash_ctx *ctx = crypto_shash_ctx(desc->tfm);
  	u8 *buf = dctx->buffer;
  
  	ghash_flush(ctx, dctx);
  	memcpy(dst, buf, GHASH_BLOCK_SIZE);
  
  	return 0;
  }
  
  static void ghash_exit_tfm(struct crypto_tfm *tfm)
  {
  	struct ghash_ctx *ctx = crypto_tfm_ctx(tfm);
  	if (ctx->gf128)
  		gf128mul_free_4k(ctx->gf128);
  }
  
  static struct shash_alg ghash_alg = {
  	.digestsize	= GHASH_DIGEST_SIZE,
  	.init		= ghash_init,
  	.update		= ghash_update,
  	.final		= ghash_final,
  	.setkey		= ghash_setkey,
  	.descsize	= sizeof(struct ghash_desc_ctx),
  	.base		= {
  		.cra_name		= "ghash",
  		.cra_driver_name	= "ghash-generic",
  		.cra_priority		= 100,

  		.cra_blocksize		= GHASH_BLOCK_SIZE,
  		.cra_ctxsize		= sizeof(struct ghash_ctx),
  		.cra_module		= THIS_MODULE,

  		.cra_exit		= ghash_exit_tfm,
  	},
  };
  
  static int __init ghash_mod_init(void)
  {
  	return crypto_register_shash(&ghash_alg);
  }
  
  static void __exit ghash_mod_exit(void)
  {
  	crypto_unregister_shash(&ghash_alg);
  }

  subsys_initcall(ghash_mod_init);

  module_exit(ghash_mod_exit);
  
  MODULE_LICENSE("GPL");

  MODULE_DESCRIPTION("GHASH hash function");

  MODULE_ALIAS_CRYPTO("ghash");

  MODULE_ALIAS_CRYPTO("ghash-generic");