/*
   * CMAC: Cipher Block Mode for Authentication
   *
   * Copyright © 2013 Jussi Kivilinna <jussi.kivilinna@iki.fi>
   *
   * Based on work by:
   *  Copyright © 2013 Tom St Denis <tstdenis@elliptictech.com>
   * Based on crypto/xcbc.c:
   *  Copyright © 2006 USAGI/WIDE Project,
   *   Author: Kazunori Miyazawa <miyazawa@linux-ipv6.org>
   *
   * 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/internal/hash.h>
  #include <linux/err.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  
  /*
   * +------------------------
   * | <parent tfm>
   * +------------------------
   * | cmac_tfm_ctx
   * +------------------------
   * | consts (block size * 2)
   * +------------------------
   */
  struct cmac_tfm_ctx {
  	struct crypto_cipher *child;
  	u8 ctx[];
  };
  
  /*
   * +------------------------
   * | <shash desc>
   * +------------------------
   * | cmac_desc_ctx
   * +------------------------
   * | odds (block size)
   * +------------------------
   * | prev (block size)
   * +------------------------
   */
  struct cmac_desc_ctx {
  	unsigned int len;
  	u8 ctx[];
  };
  
  static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
  				     const u8 *inkey, unsigned int keylen)
  {
  	unsigned long alignmask = crypto_shash_alignmask(parent);
  	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
  	unsigned int bs = crypto_shash_blocksize(parent);
  	__be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
  	u64 _const[2];
  	int i, err = 0;
  	u8 msb_mask, gfmask;
  
  	err = crypto_cipher_setkey(ctx->child, inkey, keylen);
  	if (err)
  		return err;
  
  	/* encrypt the zero block */
  	memset(consts, 0, bs);
  	crypto_cipher_encrypt_one(ctx->child, (u8 *)consts, (u8 *)consts);
  
  	switch (bs) {
  	case 16:
  		gfmask = 0x87;
  		_const[0] = be64_to_cpu(consts[1]);
  		_const[1] = be64_to_cpu(consts[0]);
  
  		/* gf(2^128) multiply zero-ciphertext with u and u^2 */
  		for (i = 0; i < 4; i += 2) {
  			msb_mask = ((s64)_const[1] >> 63) & gfmask;
  			_const[1] = (_const[1] << 1) | (_const[0] >> 63);
  			_const[0] = (_const[0] << 1) ^ msb_mask;
  
  			consts[i + 0] = cpu_to_be64(_const[1]);
  			consts[i + 1] = cpu_to_be64(_const[0]);
  		}
  
  		break;
  	case 8:
  		gfmask = 0x1B;
  		_const[0] = be64_to_cpu(consts[0]);
  
  		/* gf(2^64) multiply zero-ciphertext with u and u^2 */
  		for (i = 0; i < 2; i++) {
  			msb_mask = ((s64)_const[0] >> 63) & gfmask;
  			_const[0] = (_const[0] << 1) ^ msb_mask;
  
  			consts[i] = cpu_to_be64(_const[0]);
  		}
  
  		break;
  	}
  
  	return 0;
  }
  
  static int crypto_cmac_digest_init(struct shash_desc *pdesc)
  {
  	unsigned long alignmask = crypto_shash_alignmask(pdesc->tfm);
  	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
  	int bs = crypto_shash_blocksize(pdesc->tfm);
  	u8 *prev = PTR_ALIGN((void *)ctx->ctx, alignmask + 1) + bs;
  
  	ctx->len = 0;
  	memset(prev, 0, bs);
  
  	return 0;
  }
  
  static int crypto_cmac_digest_update(struct shash_desc *pdesc, const u8 *p,
  				     unsigned int len)
  {
  	struct crypto_shash *parent = pdesc->tfm;
  	unsigned long alignmask = crypto_shash_alignmask(parent);
  	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
  	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
  	struct crypto_cipher *tfm = tctx->child;
  	int bs = crypto_shash_blocksize(parent);
  	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
  	u8 *prev = odds + bs;
  
  	/* checking the data can fill the block */
  	if ((ctx->len + len) <= bs) {
  		memcpy(odds + ctx->len, p, len);
  		ctx->len += len;
  		return 0;
  	}
  
  	/* filling odds with new data and encrypting it */
  	memcpy(odds + ctx->len, p, bs - ctx->len);
  	len -= bs - ctx->len;
  	p += bs - ctx->len;
  
  	crypto_xor(prev, odds, bs);
  	crypto_cipher_encrypt_one(tfm, prev, prev);
  
  	/* clearing the length */
  	ctx->len = 0;
  
  	/* encrypting the rest of data */
  	while (len > bs) {
  		crypto_xor(prev, p, bs);
  		crypto_cipher_encrypt_one(tfm, prev, prev);
  		p += bs;
  		len -= bs;
  	}
  
  	/* keeping the surplus of blocksize */
  	if (len) {
  		memcpy(odds, p, len);
  		ctx->len = len;
  	}
  
  	return 0;
  }
  
  static int crypto_cmac_digest_final(struct shash_desc *pdesc, u8 *out)
  {
  	struct crypto_shash *parent = pdesc->tfm;
  	unsigned long alignmask = crypto_shash_alignmask(parent);
  	struct cmac_tfm_ctx *tctx = crypto_shash_ctx(parent);
  	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
  	struct crypto_cipher *tfm = tctx->child;
  	int bs = crypto_shash_blocksize(parent);
  	u8 *consts = PTR_ALIGN((void *)tctx->ctx, alignmask + 1);
  	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
  	u8 *prev = odds + bs;
  	unsigned int offset = 0;
  
  	if (ctx->len != bs) {
  		unsigned int rlen;
  		u8 *p = odds + ctx->len;
  
  		*p = 0x80;
  		p++;
  
  		rlen = bs - ctx->len - 1;
  		if (rlen)
  			memset(p, 0, rlen);
  
  		offset += bs;
  	}
  
  	crypto_xor(prev, odds, bs);
  	crypto_xor(prev, consts + offset, bs);
  
  	crypto_cipher_encrypt_one(tfm, out, prev);
  
  	return 0;
  }
  
  static int cmac_init_tfm(struct crypto_tfm *tfm)
  {
  	struct crypto_cipher *cipher;
  	struct crypto_instance *inst = (void *)tfm->__crt_alg;
  	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
  	struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
  
  	cipher = crypto_spawn_cipher(spawn);
  	if (IS_ERR(cipher))
  		return PTR_ERR(cipher);
  
  	ctx->child = cipher;
  
  	return 0;
  };
  
  static void cmac_exit_tfm(struct crypto_tfm *tfm)
  {
  	struct cmac_tfm_ctx *ctx = crypto_tfm_ctx(tfm);
  	crypto_free_cipher(ctx->child);
  }
  
  static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
  {
  	struct shash_instance *inst;
  	struct crypto_alg *alg;
  	unsigned long alignmask;
  	int err;
  
  	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH);
  	if (err)
  		return err;
  
  	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
  				  CRYPTO_ALG_TYPE_MASK);
  	if (IS_ERR(alg))
  		return PTR_ERR(alg);
  
  	switch (alg->cra_blocksize) {
  	case 16:
  	case 8:
  		break;
  	default:
  		goto out_put_alg;
  	}
  
  	inst = shash_alloc_instance("cmac", alg);
  	err = PTR_ERR(inst);
  	if (IS_ERR(inst))
  		goto out_put_alg;
  
  	err = crypto_init_spawn(shash_instance_ctx(inst), alg,
  				shash_crypto_instance(inst),
  				CRYPTO_ALG_TYPE_MASK);
  	if (err)
  		goto out_free_inst;
  
  	alignmask = alg->cra_alignmask | (sizeof(long) - 1);
  	inst->alg.base.cra_alignmask = alignmask;
  	inst->alg.base.cra_priority = alg->cra_priority;
  	inst->alg.base.cra_blocksize = alg->cra_blocksize;
  
  	inst->alg.digestsize = alg->cra_blocksize;
  	inst->alg.descsize =
  		ALIGN(sizeof(struct cmac_desc_ctx), crypto_tfm_ctx_alignment())
  		+ (alignmask & ~(crypto_tfm_ctx_alignment() - 1))
  		+ alg->cra_blocksize * 2;
  
  	inst->alg.base.cra_ctxsize =
  		ALIGN(sizeof(struct cmac_tfm_ctx), alignmask + 1)
  		+ alg->cra_blocksize * 2;
  
  	inst->alg.base.cra_init = cmac_init_tfm;
  	inst->alg.base.cra_exit = cmac_exit_tfm;
  
  	inst->alg.init = crypto_cmac_digest_init;
  	inst->alg.update = crypto_cmac_digest_update;
  	inst->alg.final = crypto_cmac_digest_final;
  	inst->alg.setkey = crypto_cmac_digest_setkey;
  
  	err = shash_register_instance(tmpl, inst);
  	if (err) {
  out_free_inst:
  		shash_free_instance(shash_crypto_instance(inst));
  	}
  
  out_put_alg:
  	crypto_mod_put(alg);
  	return err;
  }
  
  static struct crypto_template crypto_cmac_tmpl = {
  	.name = "cmac",
  	.create = cmac_create,
  	.free = shash_free_instance,
  	.module = THIS_MODULE,
  };
  
  static int __init crypto_cmac_module_init(void)
  {
  	return crypto_register_template(&crypto_cmac_tmpl);
  }
  
  static void __exit crypto_cmac_module_exit(void)
  {
  	crypto_unregister_template(&crypto_cmac_tmpl);
  }
  
  module_init(crypto_cmac_module_init);
  module_exit(crypto_cmac_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("CMAC keyed hash algorithm");