/*
   * Poly1305 authenticator algorithm, RFC7539
   *
   * Copyright (C) 2015 Martin Willi
   *
   * Based on public domain code by Andrew Moon and Daniel J. Bernstein.
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   */
  
  #include <crypto/algapi.h>
  #include <crypto/internal/hash.h>

  #include <crypto/poly1305.h>

  #include <linux/crypto.h>
  #include <linux/kernel.h>
  #include <linux/module.h>

  static inline u64 mlt(u64 a, u64 b)
  {
  	return a * b;
  }
  
  static inline u32 sr(u64 v, u_char n)
  {
  	return v >> n;
  }
  
  static inline u32 and(u32 v, u32 mask)
  {
  	return v & mask;
  }
  
  static inline u32 le32_to_cpuvp(const void *p)
  {
  	return le32_to_cpup(p);
  }

  int crypto_poly1305_init(struct shash_desc *desc)

  {
  	struct poly1305_desc_ctx *dctx = shash_desc_ctx(desc);
  
  	memset(dctx->h, 0, sizeof(dctx->h));
  	dctx->buflen = 0;

  	dctx->rset = false;
  	dctx->sset = false;

  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(crypto_poly1305_init);

  int crypto_poly1305_setkey(struct crypto_shash *tfm,

  			   const u8 *key, unsigned int keylen)
  {

  	/* Poly1305 requires a unique key for each tag, which implies that
  	 * we can't set it on the tfm that gets accessed by multiple users
  	 * simultaneously. Instead we expect the key as the first 32 bytes in
  	 * the update() call. */
  	return -ENOTSUPP;
  }

  EXPORT_SYMBOL_GPL(crypto_poly1305_setkey);

  static void poly1305_setrkey(struct poly1305_desc_ctx *dctx, const u8 *key)
  {

  	/* r &= 0xffffffc0ffffffc0ffffffc0fffffff */

  	dctx->r[0] = (le32_to_cpuvp(key +  0) >> 0) & 0x3ffffff;
  	dctx->r[1] = (le32_to_cpuvp(key +  3) >> 2) & 0x3ffff03;
  	dctx->r[2] = (le32_to_cpuvp(key +  6) >> 4) & 0x3ffc0ff;
  	dctx->r[3] = (le32_to_cpuvp(key +  9) >> 6) & 0x3f03fff;
  	dctx->r[4] = (le32_to_cpuvp(key + 12) >> 8) & 0x00fffff;
  }

  static void poly1305_setskey(struct poly1305_desc_ctx *dctx, const u8 *key)
  {
  	dctx->s[0] = le32_to_cpuvp(key +  0);
  	dctx->s[1] = le32_to_cpuvp(key +  4);
  	dctx->s[2] = le32_to_cpuvp(key +  8);
  	dctx->s[3] = le32_to_cpuvp(key + 12);

  }

  unsigned int crypto_poly1305_setdesckey(struct poly1305_desc_ctx *dctx,
  					const u8 *src, unsigned int srclen)

  {

  	if (!dctx->sset) {

  		if (!dctx->rset && srclen >= POLY1305_BLOCK_SIZE) {
  			poly1305_setrkey(dctx, src);
  			src += POLY1305_BLOCK_SIZE;
  			srclen -= POLY1305_BLOCK_SIZE;
  			dctx->rset = true;
  		}
  		if (srclen >= POLY1305_BLOCK_SIZE) {
  			poly1305_setskey(dctx, src);
  			src += POLY1305_BLOCK_SIZE;
  			srclen -= POLY1305_BLOCK_SIZE;
  			dctx->sset = true;
  		}
  	}

  	return srclen;
  }
  EXPORT_SYMBOL_GPL(crypto_poly1305_setdesckey);
  
  static unsigned int poly1305_blocks(struct poly1305_desc_ctx *dctx,
  				    const u8 *src, unsigned int srclen,
  				    u32 hibit)
  {
  	u32 r0, r1, r2, r3, r4;
  	u32 s1, s2, s3, s4;
  	u32 h0, h1, h2, h3, h4;
  	u64 d0, d1, d2, d3, d4;
  	unsigned int datalen;
  
  	if (unlikely(!dctx->sset)) {
  		datalen = crypto_poly1305_setdesckey(dctx, src, srclen);
  		src += srclen - datalen;
  		srclen = datalen;
  	}

  
  	r0 = dctx->r[0];
  	r1 = dctx->r[1];
  	r2 = dctx->r[2];
  	r3 = dctx->r[3];
  	r4 = dctx->r[4];

  
  	s1 = r1 * 5;
  	s2 = r2 * 5;
  	s3 = r3 * 5;
  	s4 = r4 * 5;
  
  	h0 = dctx->h[0];
  	h1 = dctx->h[1];
  	h2 = dctx->h[2];
  	h3 = dctx->h[3];
  	h4 = dctx->h[4];
  
  	while (likely(srclen >= POLY1305_BLOCK_SIZE)) {
  
  		/* h += m[i] */
  		h0 += (le32_to_cpuvp(src +  0) >> 0) & 0x3ffffff;
  		h1 += (le32_to_cpuvp(src +  3) >> 2) & 0x3ffffff;
  		h2 += (le32_to_cpuvp(src +  6) >> 4) & 0x3ffffff;
  		h3 += (le32_to_cpuvp(src +  9) >> 6) & 0x3ffffff;
  		h4 += (le32_to_cpuvp(src + 12) >> 8) | hibit;
  
  		/* h *= r */
  		d0 = mlt(h0, r0) + mlt(h1, s4) + mlt(h2, s3) +
  		     mlt(h3, s2) + mlt(h4, s1);
  		d1 = mlt(h0, r1) + mlt(h1, r0) + mlt(h2, s4) +
  		     mlt(h3, s3) + mlt(h4, s2);
  		d2 = mlt(h0, r2) + mlt(h1, r1) + mlt(h2, r0) +
  		     mlt(h3, s4) + mlt(h4, s3);
  		d3 = mlt(h0, r3) + mlt(h1, r2) + mlt(h2, r1) +
  		     mlt(h3, r0) + mlt(h4, s4);
  		d4 = mlt(h0, r4) + mlt(h1, r3) + mlt(h2, r2) +
  		     mlt(h3, r1) + mlt(h4, r0);
  
  		/* (partial) h %= p */
  		d1 += sr(d0, 26);     h0 = and(d0, 0x3ffffff);
  		d2 += sr(d1, 26);     h1 = and(d1, 0x3ffffff);
  		d3 += sr(d2, 26);     h2 = and(d2, 0x3ffffff);
  		d4 += sr(d3, 26);     h3 = and(d3, 0x3ffffff);
  		h0 += sr(d4, 26) * 5; h4 = and(d4, 0x3ffffff);
  		h1 += h0 >> 26;       h0 = h0 & 0x3ffffff;
  
  		src += POLY1305_BLOCK_SIZE;
  		srclen -= POLY1305_BLOCK_SIZE;
  	}
  
  	dctx->h[0] = h0;
  	dctx->h[1] = h1;
  	dctx->h[2] = h2;
  	dctx->h[3] = h3;
  	dctx->h[4] = h4;
  
  	return srclen;
  }

  int crypto_poly1305_update(struct shash_desc *desc,

  			   const u8 *src, unsigned int srclen)
  {
  	struct poly1305_desc_ctx *dctx = shash_desc_ctx(desc);

  	unsigned int bytes;
  
  	if (unlikely(dctx->buflen)) {
  		bytes = min(srclen, POLY1305_BLOCK_SIZE - dctx->buflen);
  		memcpy(dctx->buf + dctx->buflen, src, bytes);
  		src += bytes;
  		srclen -= bytes;
  		dctx->buflen += bytes;
  
  		if (dctx->buflen == POLY1305_BLOCK_SIZE) {

  			poly1305_blocks(dctx, dctx->buf,

  					POLY1305_BLOCK_SIZE, 1 << 24);
  			dctx->buflen = 0;
  		}
  	}
  
  	if (likely(srclen >= POLY1305_BLOCK_SIZE)) {

  		bytes = poly1305_blocks(dctx, src, srclen, 1 << 24);

  		src += srclen - bytes;
  		srclen = bytes;
  	}
  
  	if (unlikely(srclen)) {
  		dctx->buflen = srclen;
  		memcpy(dctx->buf, src, srclen);
  	}
  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(crypto_poly1305_update);

  int crypto_poly1305_final(struct shash_desc *desc, u8 *dst)

  {
  	struct poly1305_desc_ctx *dctx = shash_desc_ctx(desc);

  	__le32 *mac = (__le32 *)dst;
  	u32 h0, h1, h2, h3, h4;
  	u32 g0, g1, g2, g3, g4;
  	u32 mask;
  	u64 f = 0;

  	if (unlikely(!dctx->sset))
  		return -ENOKEY;

  	if (unlikely(dctx->buflen)) {
  		dctx->buf[dctx->buflen++] = 1;
  		memset(dctx->buf + dctx->buflen, 0,
  		       POLY1305_BLOCK_SIZE - dctx->buflen);

  		poly1305_blocks(dctx, dctx->buf, POLY1305_BLOCK_SIZE, 0);

  	}
  
  	/* fully carry h */
  	h0 = dctx->h[0];
  	h1 = dctx->h[1];
  	h2 = dctx->h[2];
  	h3 = dctx->h[3];
  	h4 = dctx->h[4];
  
  	h2 += (h1 >> 26);     h1 = h1 & 0x3ffffff;
  	h3 += (h2 >> 26);     h2 = h2 & 0x3ffffff;
  	h4 += (h3 >> 26);     h3 = h3 & 0x3ffffff;
  	h0 += (h4 >> 26) * 5; h4 = h4 & 0x3ffffff;
  	h1 += (h0 >> 26);     h0 = h0 & 0x3ffffff;
  
  	/* compute h + -p */
  	g0 = h0 + 5;
  	g1 = h1 + (g0 >> 26);             g0 &= 0x3ffffff;
  	g2 = h2 + (g1 >> 26);             g1 &= 0x3ffffff;
  	g3 = h3 + (g2 >> 26);             g2 &= 0x3ffffff;
  	g4 = h4 + (g3 >> 26) - (1 << 26); g3 &= 0x3ffffff;
  
  	/* select h if h < p, or h + -p if h >= p */
  	mask = (g4 >> ((sizeof(u32) * 8) - 1)) - 1;
  	g0 &= mask;
  	g1 &= mask;
  	g2 &= mask;
  	g3 &= mask;
  	g4 &= mask;
  	mask = ~mask;
  	h0 = (h0 & mask) | g0;
  	h1 = (h1 & mask) | g1;
  	h2 = (h2 & mask) | g2;
  	h3 = (h3 & mask) | g3;
  	h4 = (h4 & mask) | g4;
  
  	/* h = h % (2^128) */
  	h0 = (h0 >>  0) | (h1 << 26);
  	h1 = (h1 >>  6) | (h2 << 20);
  	h2 = (h2 >> 12) | (h3 << 14);
  	h3 = (h3 >> 18) | (h4 <<  8);
  
  	/* mac = (h + s) % (2^128) */

  	f = (f >> 32) + h0 + dctx->s[0]; mac[0] = cpu_to_le32(f);
  	f = (f >> 32) + h1 + dctx->s[1]; mac[1] = cpu_to_le32(f);
  	f = (f >> 32) + h2 + dctx->s[2]; mac[2] = cpu_to_le32(f);
  	f = (f >> 32) + h3 + dctx->s[3]; mac[3] = cpu_to_le32(f);

  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(crypto_poly1305_final);

  
  static struct shash_alg poly1305_alg = {
  	.digestsize	= POLY1305_DIGEST_SIZE,

  	.init		= crypto_poly1305_init,
  	.update		= crypto_poly1305_update,
  	.final		= crypto_poly1305_final,
  	.setkey		= crypto_poly1305_setkey,

  	.descsize	= sizeof(struct poly1305_desc_ctx),
  	.base		= {
  		.cra_name		= "poly1305",
  		.cra_driver_name	= "poly1305-generic",
  		.cra_priority		= 100,
  		.cra_flags		= CRYPTO_ALG_TYPE_SHASH,
  		.cra_alignmask		= sizeof(u32) - 1,
  		.cra_blocksize		= POLY1305_BLOCK_SIZE,

  		.cra_module		= THIS_MODULE,
  	},
  };
  
  static int __init poly1305_mod_init(void)
  {
  	return crypto_register_shash(&poly1305_alg);
  }
  
  static void __exit poly1305_mod_exit(void)
  {
  	crypto_unregister_shash(&poly1305_alg);
  }
  
  module_init(poly1305_mod_init);
  module_exit(poly1305_mod_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");
  MODULE_DESCRIPTION("Poly1305 authenticator");
  MODULE_ALIAS_CRYPTO("poly1305");
  MODULE_ALIAS_CRYPTO("poly1305-generic");