text: /* $OpenBSD: cipher-ctr.c,v 1.11 2010/10/01 23:05:32 djm Exp $ */
  /*
   * Copyright (c) 2003 Markus Friedl <markus@openbsd.org>
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  #include "includes.h"
  
  #ifndef OPENSSL_HAVE_EVPCTR
  #include <sys/types.h>
  
  #include <stdarg.h>
  #include <string.h>
  
  #include <openssl/evp.h>
  
  #include "xmalloc.h"
  #include "log.h"
  
  /* compatibility with old or broken OpenSSL versions */
  #include "openbsd-compat/openssl-compat.h"
  
  #ifndef USE_BUILTIN_RIJNDAEL
  #include <openssl/aes.h>
  #endif
  
  struct ssh_aes_ctr_ctx
  {
  	AES_KEY		aes_ctx;
  	u_char		aes_counter[AES_BLOCK_SIZE];
  };
  
  /*
   * increment counter 'ctr',
   * the counter is of size 'len' bytes and stored in network-byte-order.
   * (LSB at ctr[len-1], MSB at ctr[0])
   */
  static void
  ssh_ctr_inc(u_char *ctr, size_t len)
  {
  	int i;
  
  	for (i = len - 1; i >= 0; i--)
  		if (++ctr[i])	/* continue on overflow */
  			return;
  }
  
  static int
  ssh_aes_ctr(EVP_CIPHER_CTX *ctx, u_char *dest, const u_char *src,
      LIBCRYPTO_EVP_INL_TYPE len)
  {
  	struct ssh_aes_ctr_ctx *c;
  	size_t n = 0;
  	u_char buf[AES_BLOCK_SIZE];
  
  	if (len == 0)
  		return (1);
  	if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) == NULL)
  		return (0);
  
  	while ((len--) > 0) {
  		if (n == 0) {
  			AES_encrypt(c->aes_counter, buf, &c->aes_ctx);
  			ssh_ctr_inc(c->aes_counter, AES_BLOCK_SIZE);
  		}
  		*(dest++) = *(src++) ^ buf[n];
  		n = (n + 1) % AES_BLOCK_SIZE;
  	}
  	return (1);
  }
  
  static int
  ssh_aes_ctr_init(EVP_CIPHER_CTX *ctx, const u_char *key, const u_char *iv,
      int enc)
  {
  	struct ssh_aes_ctr_ctx *c;
  
  	if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) == NULL) {
  		c = xmalloc(sizeof(*c));
  		EVP_CIPHER_CTX_set_app_data(ctx, c);
  	}
  	if (key != NULL)
  		AES_set_encrypt_key(key, EVP_CIPHER_CTX_key_length(ctx) * 8,
  		    &c->aes_ctx);
  	if (iv != NULL)
  		memcpy(c->aes_counter, iv, AES_BLOCK_SIZE);
  	return (1);
  }
  
  static int
  ssh_aes_ctr_cleanup(EVP_CIPHER_CTX *ctx)
  {
  	struct ssh_aes_ctr_ctx *c;
  
  	if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) != NULL) {
  		memset(c, 0, sizeof(*c));
  		xfree(c);
  		EVP_CIPHER_CTX_set_app_data(ctx, NULL);
  	}
  	return (1);
  }
  
  void
  ssh_aes_ctr_iv(EVP_CIPHER_CTX *evp, int doset, u_char * iv, size_t len)
  {
  	struct ssh_aes_ctr_ctx *c;
  
  	if ((c = EVP_CIPHER_CTX_get_app_data(evp)) == NULL)
  		fatal("ssh_aes_ctr_iv: no context");
  	if (doset)
  		memcpy(c->aes_counter, iv, len);
  	else
  		memcpy(iv, c->aes_counter, len);
  }
  
  const EVP_CIPHER *
  evp_aes_128_ctr(void)
  {
  	static EVP_CIPHER aes_ctr;
  
  	memset(&aes_ctr, 0, sizeof(EVP_CIPHER));
  	aes_ctr.nid = NID_undef;
  	aes_ctr.block_size = AES_BLOCK_SIZE;
  	aes_ctr.iv_len = AES_BLOCK_SIZE;
  	aes_ctr.key_len = 16;
  	aes_ctr.init = ssh_aes_ctr_init;
  	aes_ctr.cleanup = ssh_aes_ctr_cleanup;
  	aes_ctr.do_cipher = ssh_aes_ctr;
  #ifndef SSH_OLD_EVP
  	aes_ctr.flags = EVP_CIPH_CBC_MODE | EVP_CIPH_VARIABLE_LENGTH |
  	    EVP_CIPH_ALWAYS_CALL_INIT | EVP_CIPH_CUSTOM_IV;
  #endif
  	return (&aes_ctr);
  }
  
  #endif /* OPENSSL_HAVE_EVPCTR */
  