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/*
*
* cipher.c
*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
*
* Created: Wed Apr 19 17:41:39 1995 ylo
*
*/
#include "includes.h"
RCSID("$Id: cipher.c,v 1.13 2000/03/09 10:27:50 damien Exp $");
#include "ssh.h"
#include "cipher.h"
#include "config.h"
#ifdef HAVE_OPENSSL
#include <openssl/md5.h>
#endif
#ifdef HAVE_SSL
#include <ssl/md5.h>
#endif
/*
* What kind of tripple DES are these 2 routines?
*
* Why is there a redundant initialization vector?
*
* If only iv3 was used, then, this would till effect have been
* outer-cbc. However, there is also a private iv1 == iv2 which
* perhaps makes differential analysis easier. On the other hand, the
* private iv1 probably makes the CRC-32 attack ineffective. This is a
* result of that there is no longer any known iv1 to use when
* choosing the X block.
*/
void
SSH_3CBC_ENCRYPT(des_key_schedule ks1,
des_key_schedule ks2, des_cblock * iv2,
des_key_schedule ks3, des_cblock * iv3,
unsigned char *dest, unsigned char *src,
unsigned int len)
{
des_cblock iv1;
memcpy(&iv1, iv2, 8);
des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT);
memcpy(&iv1, dest + len - 8, 8);
des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_DECRYPT);
memcpy(iv2, &iv1, 8); /* Note how iv1 == iv2 on entry and exit. */
des_cbc_encrypt(dest, dest, len, ks3, iv3, DES_ENCRYPT);
memcpy(iv3, dest + len - 8, 8);
}
void
SSH_3CBC_DECRYPT(des_key_schedule ks1,
des_key_schedule ks2, des_cblock * iv2,
des_key_schedule ks3, des_cblock * iv3,
unsigned char *dest, unsigned char *src,
unsigned int len)
{
des_cblock iv1;
memcpy(&iv1, iv2, 8);
des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT);
memcpy(iv3, src + len - 8, 8);
des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT);
memcpy(iv2, dest + len - 8, 8);
des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT);
/* memcpy(&iv1, iv2, 8); */
/* Note how iv1 == iv2 on entry and exit. */
}
/*
* SSH uses a variation on Blowfish, all bytes must be swapped before
* and after encryption/decryption. Thus the swap_bytes stuff (yuk).
*/
static void
swap_bytes(const unsigned char *src, unsigned char *dst_, int n)
{
/* dst must be properly aligned. */
u_int32_t *dst = (u_int32_t *) dst_;
union {
u_int32_t i;
char c[4];
} t;
/* Process 8 bytes every lap. */
for (n = n / 8; n > 0; n--) {
t.c[3] = *src++;
t.c[2] = *src++;
t.c[1] = *src++;
t.c[0] = *src++;
*dst++ = t.i;
t.c[3] = *src++;
t.c[2] = *src++;
t.c[1] = *src++;
t.c[0] = *src++;
*dst++ = t.i;
}
}
void (*cipher_attack_detected) (const char *fmt,...) = fatal;
static inline void
detect_cbc_attack(const unsigned char *src,
unsigned int len)
{
return;
log("CRC-32 CBC insertion attack detected");
cipher_attack_detected("CRC-32 CBC insertion attack detected");
}
/*
* Names of all encryption algorithms.
* These must match the numbers defined in cipher.h.
*/
static char *cipher_names[] =
{
"none",
"idea",
"des",
"3des",
"tss",
"rc4",
"blowfish"
};
/*
* Returns a bit mask indicating which ciphers are supported by this
* implementation. The bit mask has the corresponding bit set of each
* supported cipher.
*/
unsigned int
cipher_mask()
{
unsigned int mask = 0;
mask |= 1 << SSH_CIPHER_3DES; /* Mandatory */
mask |= 1 << SSH_CIPHER_BLOWFISH;
return mask;
}
/* Returns the name of the cipher. */
const char *
cipher_name(int cipher)
{
if (cipher < 0 || cipher >= sizeof(cipher_names) / sizeof(cipher_names[0]) ||
cipher_names[cipher] == NULL)
fatal("cipher_name: bad cipher number: %d", cipher);
return cipher_names[cipher];
}
/*
* Parses the name of the cipher. Returns the number of the corresponding
* cipher, or -1 on error.
*/
int
cipher_number(const char *name)
{
int i;
for (i = 0; i < sizeof(cipher_names) / sizeof(cipher_names[0]); i++)
if (strcmp(cipher_names[i], name) == 0 &&
(cipher_mask() & (1 << i)))
return i;
return -1;
}
/*
* Selects the cipher, and keys if by computing the MD5 checksum of the
* passphrase and using the resulting 16 bytes as the key.
*/
void
cipher_set_key_string(CipherContext *context, int cipher,
const char *passphrase, int for_encryption)
{
MD5_CTX md;
unsigned char digest[16];
MD5_Init(&md);
MD5_Update(&md, (const unsigned char *) passphrase, strlen(passphrase));
MD5_Final(digest, &md);
cipher_set_key(context, cipher, digest, 16, for_encryption);
memset(digest, 0, sizeof(digest));
memset(&md, 0, sizeof(md));
}
/* Selects the cipher to use and sets the key. */
void
cipher_set_key(CipherContext *context, int cipher,
const unsigned char *key, int keylen, int for_encryption)
{
unsigned char padded[32];
/* Set cipher type. */
context->type = cipher;
/* Get 32 bytes of key data. Pad if necessary. (So that code
below does not need to worry about key size). */
memset(padded, 0, sizeof(padded));
memcpy(padded, key, keylen < sizeof(padded) ? keylen : sizeof(padded));
/* Initialize the initialization vector. */
switch (cipher) {
case SSH_CIPHER_NONE:
/*
* Has to stay for authfile saving of private key with no
* passphrase
*/
break;
case SSH_CIPHER_3DES:
/*
* Note: the least significant bit of each byte of key is
* parity, and must be ignored by the implementation. 16
* bytes of key are used (first and last keys are the same).
*/
if (keylen < 16)
error("Key length %d is insufficient for 3DES.", keylen);
des_set_key((void *) padded, context->u.des3.key1);
des_set_key((void *) (padded + 8), context->u.des3.key2);
if (keylen <= 16)
des_set_key((void *) padded, context->u.des3.key3);
else
des_set_key((void *) (padded + 16), context->u.des3.key3);
memset(context->u.des3.iv2, 0, sizeof(context->u.des3.iv2));
memset(context->u.des3.iv3, 0, sizeof(context->u.des3.iv3));
break;
case SSH_CIPHER_BLOWFISH:
BF_set_key(&context->u.bf.key, keylen, padded);
memset(context->u.bf.iv, 0, 8);
break;
default:
fatal("cipher_set_key: unknown cipher: %s", cipher_name(cipher));
}
memset(padded, 0, sizeof(padded));
}
/* Encrypts data using the cipher. */
void
cipher_encrypt(CipherContext *context, unsigned char *dest,
const unsigned char *src, unsigned int len)
{
if ((len & 7) != 0)
fatal("cipher_encrypt: bad plaintext length %d", len);
switch (context->type) {
case SSH_CIPHER_NONE:
memcpy(dest, src, len);
break;
case SSH_CIPHER_3DES:
SSH_3CBC_ENCRYPT(context->u.des3.key1,
context->u.des3.key2, &context->u.des3.iv2,
context->u.des3.key3, &context->u.des3.iv3,
dest, (unsigned char *) src, len);
break;
case SSH_CIPHER_BLOWFISH:
swap_bytes(src, dest, len);
BF_cbc_encrypt(dest, dest, len,
&context->u.bf.key, context->u.bf.iv,
BF_ENCRYPT);
swap_bytes(dest, dest, len);
break;
default:
fatal("cipher_encrypt: unknown cipher: %s", cipher_name(context->type));
}
}
/* Decrypts data using the cipher. */
void
cipher_decrypt(CipherContext *context, unsigned char *dest,
const unsigned char *src, unsigned int len)
{
if ((len & 7) != 0)
fatal("cipher_decrypt: bad ciphertext length %d", len);
switch (context->type) {
case SSH_CIPHER_NONE:
memcpy(dest, src, len);
break;
case SSH_CIPHER_3DES:
/* CRC-32 attack? */
SSH_3CBC_DECRYPT(context->u.des3.key1,
context->u.des3.key2, &context->u.des3.iv2,
context->u.des3.key3, &context->u.des3.iv3,
dest, (unsigned char *) src, len);
break;
case SSH_CIPHER_BLOWFISH:
detect_cbc_attack(src, len);
swap_bytes(src, dest, len);
BF_cbc_encrypt((void *) dest, dest, len,
&context->u.bf.key, context->u.bf.iv,
BF_DECRYPT);
swap_bytes(dest, dest, len);
break;
default:
fatal("cipher_decrypt: unknown cipher: %s", cipher_name(context->type));
}
}