cipher-ctr.c

   1 /* $OpenBSD: cipher-ctr.c,v 1.10 2006/08/03 03:34:42 deraadt 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 <sys/types.h>
  20
  21 #include <stdarg.h>
  22 #include <string.h>
  23
  24 #include <openssl/evp.h>
  25
  26 #include "xmalloc.h"
  27 #include "log.h"
  28
  29 /* compatibility with old or broken OpenSSL versions */
  30 #include "openbsd-compat/openssl-compat.h"
  31
  32 #ifndef USE_BUILTIN_RIJNDAEL
  33 #include <openssl/aes.h>
  34 #endif
  35
  36 const EVP_CIPHER *evp_aes_128_ctr(void);
  37 void ssh_aes_ctr_iv(EVP_CIPHER_CTX *, int, u_char *, u_int);
  38
  39 struct ssh_aes_ctr_ctx
  40 {
  41         AES_KEY         aes_ctx;
  42         u_char          aes_counter[AES_BLOCK_SIZE];
  43 };
  44
  45 /*
  46  * increment counter 'ctr',
  47  * the counter is of size 'len' bytes and stored in network-byte-order.
  48  * (LSB at ctr[len-1], MSB at ctr[0])
  49  */
  50 static void
  51 ssh_ctr_inc(u_char *ctr, u_int len)
  52 {
  53         int i;
  54
  55         for (i = len - 1; i >= 0; i--)
  56                 if (++ctr[i])   /* continue on overflow */
  57                         return;
  58 }
  59
  60 static int
  61 ssh_aes_ctr(EVP_CIPHER_CTX *ctx, u_char *dest, const u_char *src,
  62     u_int len)
  63 {
  64         struct ssh_aes_ctr_ctx *c;
  65         u_int n = 0;
  66         u_char buf[AES_BLOCK_SIZE];
  67
  68         if (len == 0)
  69                 return (1);
  70         if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) == NULL)
  71                 return (0);
  72
  73         while ((len--) > 0) {
  74                 if (n == 0) {
  75                         AES_encrypt(c->aes_counter, buf, &c->aes_ctx);
  76                         ssh_ctr_inc(c->aes_counter, AES_BLOCK_SIZE);
  77                 }
  78                 *(dest++) = *(src++) ^ buf[n];
  79                 n = (n + 1) % AES_BLOCK_SIZE;
  80         }
  81         return (1);
  82 }
  83
  84 static int
  85 ssh_aes_ctr_init(EVP_CIPHER_CTX *ctx, const u_char *key, const u_char *iv,
  86     int enc)
  87 {
  88         struct ssh_aes_ctr_ctx *c;
  89
  90         if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) == NULL) {
  91                 c = xmalloc(sizeof(*c));
  92                 EVP_CIPHER_CTX_set_app_data(ctx, c);
  93         }
  94         if (key != NULL)
  95                 AES_set_encrypt_key(key, EVP_CIPHER_CTX_key_length(ctx) * 8,
  96                     &c->aes_ctx);
  97         if (iv != NULL)
  98                 memcpy(c->aes_counter, iv, AES_BLOCK_SIZE);
  99         return (1);
 100 }
 101
 102 static int
 103 ssh_aes_ctr_cleanup(EVP_CIPHER_CTX *ctx)
 104 {
 105         struct ssh_aes_ctr_ctx *c;
 106
 107         if ((c = EVP_CIPHER_CTX_get_app_data(ctx)) != NULL) {
 108                 memset(c, 0, sizeof(*c));
 109                 xfree(c);
 110                 EVP_CIPHER_CTX_set_app_data(ctx, NULL);
 111         }
 112         return (1);
 113 }
 114
 115 void
 116 ssh_aes_ctr_iv(EVP_CIPHER_CTX *evp, int doset, u_char * iv, u_int len)
 117 {
 118         struct ssh_aes_ctr_ctx *c;
 119
 120         if ((c = EVP_CIPHER_CTX_get_app_data(evp)) == NULL)
 121                 fatal("ssh_aes_ctr_iv: no context");
 122         if (doset)
 123                 memcpy(c->aes_counter, iv, len);
 124         else
 125                 memcpy(iv, c->aes_counter, len);
 126 }
 127
 128 const EVP_CIPHER *
 129 evp_aes_128_ctr(void)
 130 {
 131         static EVP_CIPHER aes_ctr;
 132
 133         memset(&aes_ctr, 0, sizeof(EVP_CIPHER));
 134         aes_ctr.nid = NID_undef;
 135         aes_ctr.block_size = AES_BLOCK_SIZE;
 136         aes_ctr.iv_len = AES_BLOCK_SIZE;
 137         aes_ctr.key_len = 16;
 138         aes_ctr.init = ssh_aes_ctr_init;
 139         aes_ctr.cleanup = ssh_aes_ctr_cleanup;
 140         aes_ctr.do_cipher = ssh_aes_ctr;
 141 #ifndef SSH_OLD_EVP
 142         aes_ctr.flags = EVP_CIPH_CBC_MODE | EVP_CIPH_VARIABLE_LENGTH |
 143             EVP_CIPH_ALWAYS_CALL_INIT | EVP_CIPH_CUSTOM_IV;
 144 #endif
 145         return (&aes_ctr);
 146 }