/*
   * echainiv: Encrypted Chain IV Generator
   *

   * This generator generates an IV based on a sequence number by multiplying
   * it with a salt and then encrypting it with the same key as used to encrypt

   * the plain text.  This algorithm requires that the block size be equal
   * to the IV size.  It is mainly useful for CBC.
   *
   * This generator can only be used by algorithms where authentication
   * is performed after encryption (i.e., authenc).
   *
   * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
   *
   * 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/geniv.h>

  #include <crypto/scatterwalk.h>

  #include <crypto/skcipher.h>

  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>

  #include <linux/module.h>

  #include <linux/slab.h>

  #include <linux/string.h>

  static int echainiv_encrypt(struct aead_request *req)
  {
  	struct crypto_aead *geniv = crypto_aead_reqtfm(req);

  	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);

  	struct aead_request *subreq = aead_request_ctx(req);

  	__be64 nseqno;
  	u64 seqno;

  	u8 *info;

  	unsigned int ivsize = crypto_aead_ivsize(geniv);

  	int err;

  	if (req->cryptlen < ivsize)
  		return -EINVAL;

  	aead_request_set_tfm(subreq, ctx->child);

  	info = req->iv;

  	if (req->src != req->dst) {

  		SKCIPHER_REQUEST_ON_STACK(nreq, ctx->sknull);

  		skcipher_request_set_tfm(nreq, ctx->sknull);
  		skcipher_request_set_callback(nreq, req->base.flags,
  					      NULL, NULL);
  		skcipher_request_set_crypt(nreq, req->src, req->dst,
  					   req->assoclen + req->cryptlen,
  					   NULL);
  
  		err = crypto_skcipher_encrypt(nreq);

  		if (err)
  			return err;
  	}

  	aead_request_set_callback(subreq, req->base.flags,
  				  req->base.complete, req->base.data);

  	aead_request_set_crypt(subreq, req->dst, req->dst,

  			       req->cryptlen, info);
  	aead_request_set_ad(subreq, req->assoclen);

  	memcpy(&nseqno, info + ivsize - 8, 8);
  	seqno = be64_to_cpu(nseqno);
  	memset(info, 0, ivsize);

  	scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);

  	do {
  		u64 a;
  
  		memcpy(&a, ctx->salt + ivsize - 8, 8);
  
  		a |= 1;
  		a *= seqno;
  
  		memcpy(info + ivsize - 8, &a, 8);
  	} while ((ivsize -= 8));
  
  	return crypto_aead_encrypt(subreq);

  }

  static int echainiv_decrypt(struct aead_request *req)
  {
  	struct crypto_aead *geniv = crypto_aead_reqtfm(req);

  	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);

  	struct aead_request *subreq = aead_request_ctx(req);
  	crypto_completion_t compl;
  	void *data;

  	unsigned int ivsize = crypto_aead_ivsize(geniv);

  	if (req->cryptlen < ivsize)

  		return -EINVAL;

  	aead_request_set_tfm(subreq, ctx->child);

  
  	compl = req->base.complete;
  	data = req->base.data;

  	aead_request_set_callback(subreq, req->base.flags, compl, data);
  	aead_request_set_crypt(subreq, req->src, req->dst,
  			       req->cryptlen - ivsize, req->iv);

  	aead_request_set_ad(subreq, req->assoclen + ivsize);

  
  	scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);

  
  	return crypto_aead_decrypt(subreq);
  }

  static int echainiv_aead_create(struct crypto_template *tmpl,
  				struct rtattr **tb)

  {
  	struct aead_instance *inst;
  	struct crypto_aead_spawn *spawn;
  	struct aead_alg *alg;

  	int err;

  	inst = aead_geniv_alloc(tmpl, tb, 0, 0);

  
  	if (IS_ERR(inst))

  		return PTR_ERR(inst);

  	spawn = aead_instance_ctx(inst);
  	alg = crypto_spawn_aead_alg(spawn);

  	err = -EINVAL;

  	if (inst->alg.ivsize & (sizeof(u64) - 1) || !inst->alg.ivsize)

  		goto free_inst;

  	inst->alg.encrypt = echainiv_encrypt;

  	inst->alg.decrypt = echainiv_decrypt;

  	inst->alg.init = aead_init_geniv;
  	inst->alg.exit = aead_exit_geniv;

  	inst->alg.base.cra_ctxsize = sizeof(struct aead_geniv_ctx);

  	inst->alg.base.cra_ctxsize += inst->alg.ivsize;

  	inst->free = aead_geniv_free;

  	err = aead_register_instance(tmpl, inst);
  	if (err)
  		goto free_inst;

  out:

  	return err;
  
  free_inst:
  	aead_geniv_free(inst);
  	goto out;

  }

  static void echainiv_free(struct crypto_instance *inst)
  {
  	aead_geniv_free(aead_instance(inst));

  }
  
  static struct crypto_template echainiv_tmpl = {
  	.name = "echainiv",

  	.create = echainiv_aead_create,

  	.free = echainiv_free,
  	.module = THIS_MODULE,
  };
  
  static int __init echainiv_module_init(void)
  {
  	return crypto_register_template(&echainiv_tmpl);
  }
  
  static void __exit echainiv_module_exit(void)
  {
  	crypto_unregister_template(&echainiv_tmpl);
  }
  
  module_init(echainiv_module_init);
  module_exit(echainiv_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("Encrypted Chain IV Generator");
  MODULE_ALIAS_CRYPTO("echainiv");