cipher-ctr.c

   1 /* $OpenBSD: cipher-ctr.c,v 1.9 2006/07/22 20:48:22 stevesk Exp $ */
   2 /*
   3  * Copyright (c) 2003 Markus Friedl <markus@openbsd.org>
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17 #include "includes.h"
  18
  19 #include <string.h>
  20
  21 #include <openssl/evp.h>
  22
  23 #include "log.h"
  24 #include "xmalloc.h"
  25
  26 /* compatibility with old or broken OpenSSL versions */
  27 #include "openbsd-compat/openssl-compat.h"
  28
  29 #ifdef USE_BUILTIN_RIJNDAEL
  30 #include "rijndael.h"
  31 #define AES_KEY rijndael_ctx
  32 #define AES_BLOCK_SIZE 16
  33 #define AES_encrypt(a, b, c) rijndael_encrypt(c, a, b)
  34 #define AES_set_encrypt_key(a, b, c) rijndael_set_key(c, (char *)a, b, 1)
  35 #else
  36 #include <openssl/aes.h>
  37 #endif
  38
  39 const EVP_CIPHER *evp_aes_128_ctr(void);
  40 void ssh_aes_ctr_iv(EVP_CIPHER_CTX *, int, u_char *, u_int);
  41
  42 struct ssh_aes_ctr_ctx
  43 {
  44         AES_KEY         aes_ctx;
  45         u_char          aes_counter[AES_BLOCK_SIZE];
  46 };
  47
  48 /*
  49  * increment counter 'ctr',
  50  * the counter is of size 'len' bytes and stored in network-byte-order.
  51  * (LSB at ctr[len-1], MSB at ctr[0])
  52  */
  53 static void
  54 ssh_ctr_inc(u_char *ctr, u_int len)
  55 {
  56         int i;
  57
  58         for (i = len - 1; i >= 0; i--)
  59                 if (++ctr[i])   /* continue on overflow */
  60                         return;
  61 }
  62
  63 static int
  64 ssh_aes_ctr(EVP_CIPHER_CTX *ctx, u_char *dest, const u_char *src,
  65     u_int len)
  66 {
  67         struct ssh_aes_ctr_ctx *c;
  68         u_int n = 0;
  69         u_char buf[AES_BLOCK_SIZE];
  70
  71         if (len == 0)
  72                 return (1);
  73         if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) == NULL)
  74                 return (0);
  75
  76         while ((len--) > 0) {
  77                 if (n == 0) {
  78                         AES_encrypt(c->aes_counter, buf, &c->aes_ctx);
  79                         ssh_ctr_inc(c->aes_counter, AES_BLOCK_SIZE);
  80                 }
  81                 *(dest++) = *(src++) ^ buf[n];
  82                 n = (n + 1) % AES_BLOCK_SIZE;
  83         }
  84         return (1);
  85 }
  86
  87 static int
  88 ssh_aes_ctr_init(EVP_CIPHER_CTX *ctx, const u_char *key, const u_char *iv,
  89     int enc)
  90 {
  91         struct ssh_aes_ctr_ctx *c;
  92
  93         if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) == NULL) {
  94                 c = xmalloc(sizeof(*c));
  95                 EVP_CIPHER_CTX_set_app_data(ctx, c);
  96         }
  97         if (key != NULL)
  98                 AES_set_encrypt_key(key, EVP_CIPHER_CTX_key_length(ctx) * 8,
  99                     &c->aes_ctx);
 100         if (iv != NULL)
 101                 memcpy(c->aes_counter, iv, AES_BLOCK_SIZE);
 102         return (1);
 103 }
 104
 105 static int
 106 ssh_aes_ctr_cleanup(EVP_CIPHER_CTX *ctx)
 107 {
 108         struct ssh_aes_ctr_ctx *c;
 109
 110         if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) != NULL) {
 111                 memset(c, 0, sizeof(*c));
 112                 xfree(c);
 113                 EVP_CIPHER_CTX_set_app_data(ctx, NULL);
 114         }
 115         return (1);
 116 }
 117
 118 void
 119 ssh_aes_ctr_iv(EVP_CIPHER_CTX *evp, int doset, u_char * iv, u_int len)
 120 {
 121         struct ssh_aes_ctr_ctx *c;
 122
 123         if ((c = EVP_CIPHER_CTX_get_app_data(evp)) == NULL)
 124                 fatal("ssh_aes_ctr_iv: no context");
 125         if (doset)
 126                 memcpy(c->aes_counter, iv, len);
 127         else
 128                 memcpy(iv, c->aes_counter, len);
 129 }
 130
 131 const EVP_CIPHER *
 132 evp_aes_128_ctr(void)
 133 {
 134         static EVP_CIPHER aes_ctr;
 135
 136         memset(&aes_ctr, 0, sizeof(EVP_CIPHER));
 137         aes_ctr.nid = NID_undef;
 138         aes_ctr.block_size = AES_BLOCK_SIZE;
 139         aes_ctr.iv_len = AES_BLOCK_SIZE;
 140         aes_ctr.key_len = 16;
 141         aes_ctr.init = ssh_aes_ctr_init;
 142         aes_ctr.cleanup = ssh_aes_ctr_cleanup;
 143         aes_ctr.do_cipher = ssh_aes_ctr;
 144 #ifndef SSH_OLD_EVP
 145         aes_ctr.flags = EVP_CIPH_CBC_MODE | EVP_CIPH_VARIABLE_LENGTH |
 146             EVP_CIPH_ALWAYS_CALL_INIT | EVP_CIPH_CUSTOM_IV;
 147 #endif
 148         return (&aes_ctr);
 149 }