Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame^] | 1 | /* |
| 2 | |
| 3 | cipher.c |
| 4 | |
| 5 | Author: Tatu Ylonen <ylo@cs.hut.fi> |
| 6 | |
| 7 | Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 8 | All rights reserved |
| 9 | |
| 10 | Created: Wed Apr 19 17:41:39 1995 ylo |
| 11 | |
| 12 | */ |
| 13 | |
| 14 | #include "includes.h" |
| 15 | RCSID("$Id: cipher.c,v 1.1 1999/10/27 03:42:44 damien Exp $"); |
| 16 | |
| 17 | #include "ssh.h" |
| 18 | #include "cipher.h" |
| 19 | |
| 20 | #include <openssl/md5.h> |
| 21 | |
| 22 | /* |
| 23 | * What kind of tripple DES are these 2 routines? |
| 24 | * |
| 25 | * Why is there a redundant initialization vector? |
| 26 | * |
| 27 | * If only iv3 was used, then, this would till effect have been |
| 28 | * outer-cbc. However, there is also a private iv1 == iv2 which |
| 29 | * perhaps makes differential analysis easier. On the other hand, the |
| 30 | * private iv1 probably makes the CRC-32 attack ineffective. This is a |
| 31 | * result of that there is no longer any known iv1 to use when |
| 32 | * choosing the X block. |
| 33 | */ |
| 34 | void |
| 35 | SSH_3CBC_ENCRYPT(des_key_schedule ks1, |
| 36 | des_key_schedule ks2, des_cblock *iv2, |
| 37 | des_key_schedule ks3, des_cblock *iv3, |
| 38 | void *dest, void *src, |
| 39 | unsigned int len) |
| 40 | { |
| 41 | des_cblock iv1; |
| 42 | |
| 43 | memcpy(&iv1, iv2, 8); |
| 44 | |
| 45 | des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT); |
| 46 | memcpy(&iv1, dest + len - 8, 8); |
| 47 | |
| 48 | des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_DECRYPT); |
| 49 | memcpy(iv2, &iv1, 8); /* Note how iv1 == iv2 on entry and exit. */ |
| 50 | |
| 51 | des_cbc_encrypt(dest, dest, len, ks3, iv3, DES_ENCRYPT); |
| 52 | memcpy(iv3, dest + len - 8, 8); |
| 53 | } |
| 54 | |
| 55 | void |
| 56 | SSH_3CBC_DECRYPT(des_key_schedule ks1, |
| 57 | des_key_schedule ks2, des_cblock *iv2, |
| 58 | des_key_schedule ks3, des_cblock *iv3, |
| 59 | void *dest, void *src, |
| 60 | unsigned int len) |
| 61 | { |
| 62 | des_cblock iv1; |
| 63 | |
| 64 | memcpy(&iv1, iv2, 8); |
| 65 | |
| 66 | des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT); |
| 67 | memcpy(iv3, src + len - 8, 8); |
| 68 | |
| 69 | des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT); |
| 70 | memcpy(iv2, dest + len - 8, 8); |
| 71 | |
| 72 | des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT); |
| 73 | /* memcpy(&iv1, iv2, 8); */ /* Note how iv1 == iv2 on entry and exit. */ |
| 74 | } |
| 75 | |
| 76 | /* |
| 77 | * SSH uses a variation on Blowfish, all bytes must be swapped before |
| 78 | * and after encryption/decryption. Thus the swap_bytes stuff (yuk). |
| 79 | */ |
| 80 | static |
| 81 | void |
| 82 | swap_bytes(const unsigned char *src, unsigned char *dst_, int n) |
| 83 | { |
| 84 | u_int32_t *dst = (u_int32_t *)dst_; /* dst must be properly aligned. */ |
| 85 | union { |
| 86 | u_int32_t i; |
| 87 | char c[4]; |
| 88 | } t; |
| 89 | |
| 90 | /* assert((n & 7) == 0); */ |
| 91 | |
| 92 | /* Process 8 bytes every lap. */ |
| 93 | for (n = n / 8; n > 0; n--) |
| 94 | { |
| 95 | t.c[3] = *src++; |
| 96 | t.c[2] = *src++; |
| 97 | t.c[1] = *src++; |
| 98 | t.c[0] = *src++; |
| 99 | *dst++ = t.i; |
| 100 | |
| 101 | t.c[3] = *src++; |
| 102 | t.c[2] = *src++; |
| 103 | t.c[1] = *src++; |
| 104 | t.c[0] = *src++; |
| 105 | *dst++ = t.i; |
| 106 | } |
| 107 | } |
| 108 | |
| 109 | void (*cipher_attack_detected)(const char *fmt, ...) = fatal; |
| 110 | |
| 111 | static inline |
| 112 | void |
| 113 | detect_cbc_attack(const unsigned char *src, |
| 114 | unsigned int len) |
| 115 | { |
| 116 | return; |
| 117 | |
| 118 | log("CRC-32 CBC insertion attack detected"); |
| 119 | cipher_attack_detected("CRC-32 CBC insertion attack detected"); |
| 120 | } |
| 121 | |
| 122 | /* Names of all encryption algorithms. These must match the numbers defined |
| 123 | int cipher.h. */ |
| 124 | static char *cipher_names[] = |
| 125 | { |
| 126 | "none", |
| 127 | "idea", |
| 128 | "des", |
| 129 | "3des", |
| 130 | "tss", |
| 131 | "rc4", |
| 132 | "blowfish" |
| 133 | }; |
| 134 | |
| 135 | /* Returns a bit mask indicating which ciphers are supported by this |
| 136 | implementation. The bit mask has the corresponding bit set of each |
| 137 | supported cipher. */ |
| 138 | |
| 139 | unsigned int cipher_mask() |
| 140 | { |
| 141 | unsigned int mask = 0; |
| 142 | mask |= 1 << SSH_CIPHER_3DES; /* Mandatory */ |
| 143 | mask |= 1 << SSH_CIPHER_BLOWFISH; |
| 144 | return mask; |
| 145 | } |
| 146 | |
| 147 | /* Returns the name of the cipher. */ |
| 148 | |
| 149 | const |
| 150 | char *cipher_name(int cipher) |
| 151 | { |
| 152 | if (cipher < 0 || cipher >= sizeof(cipher_names) / sizeof(cipher_names[0]) || |
| 153 | cipher_names[cipher] == NULL) |
| 154 | fatal("cipher_name: bad cipher number: %d", cipher); |
| 155 | return cipher_names[cipher]; |
| 156 | } |
| 157 | |
| 158 | /* Parses the name of the cipher. Returns the number of the corresponding |
| 159 | cipher, or -1 on error. */ |
| 160 | |
| 161 | int |
| 162 | cipher_number(const char *name) |
| 163 | { |
| 164 | int i; |
| 165 | for (i = 0; i < sizeof(cipher_names) / sizeof(cipher_names[0]); i++) |
| 166 | if (strcmp(cipher_names[i], name) == 0 && |
| 167 | (cipher_mask() & (1 << i))) |
| 168 | return i; |
| 169 | return -1; |
| 170 | } |
| 171 | |
| 172 | /* Selects the cipher, and keys if by computing the MD5 checksum of the |
| 173 | passphrase and using the resulting 16 bytes as the key. */ |
| 174 | |
| 175 | void cipher_set_key_string(CipherContext *context, int cipher, |
| 176 | const char *passphrase, int for_encryption) |
| 177 | { |
| 178 | MD5_CTX md; |
| 179 | unsigned char digest[16]; |
| 180 | |
| 181 | MD5_Init(&md); |
| 182 | MD5_Update(&md, (const unsigned char *)passphrase, strlen(passphrase)); |
| 183 | MD5_Final(digest, &md); |
| 184 | |
| 185 | cipher_set_key(context, cipher, digest, 16, for_encryption); |
| 186 | |
| 187 | memset(digest, 0, sizeof(digest)); |
| 188 | memset(&md, 0, sizeof(md)); |
| 189 | } |
| 190 | |
| 191 | /* Selects the cipher to use and sets the key. */ |
| 192 | |
| 193 | void cipher_set_key(CipherContext *context, int cipher, |
| 194 | const unsigned char *key, int keylen, int for_encryption) |
| 195 | { |
| 196 | unsigned char padded[32]; |
| 197 | |
| 198 | /* Set cipher type. */ |
| 199 | context->type = cipher; |
| 200 | |
| 201 | /* Get 32 bytes of key data. Pad if necessary. (So that code below does |
| 202 | not need to worry about key size). */ |
| 203 | memset(padded, 0, sizeof(padded)); |
| 204 | memcpy(padded, key, keylen < sizeof(padded) ? keylen : sizeof(padded)); |
| 205 | |
| 206 | /* Initialize the initialization vector. */ |
| 207 | switch (cipher) |
| 208 | { |
| 209 | case SSH_CIPHER_NONE: |
| 210 | /* Has to stay for authfile saving of private key with no passphrase */ |
| 211 | break; |
| 212 | |
| 213 | case SSH_CIPHER_3DES: |
| 214 | /* Note: the least significant bit of each byte of key is parity, |
| 215 | and must be ignored by the implementation. 16 bytes of key are |
| 216 | used (first and last keys are the same). */ |
| 217 | if (keylen < 16) |
| 218 | error("Key length %d is insufficient for 3DES.", keylen); |
| 219 | des_set_key((void*)padded, context->u.des3.key1); |
| 220 | des_set_key((void*)(padded + 8), context->u.des3.key2); |
| 221 | if (keylen <= 16) |
| 222 | des_set_key((void*)padded, context->u.des3.key3); |
| 223 | else |
| 224 | des_set_key((void*)(padded + 16), context->u.des3.key3); |
| 225 | memset(context->u.des3.iv2, 0, sizeof(context->u.des3.iv2)); |
| 226 | memset(context->u.des3.iv3, 0, sizeof(context->u.des3.iv3)); |
| 227 | break; |
| 228 | |
| 229 | case SSH_CIPHER_BLOWFISH: |
| 230 | BF_set_key(&context->u.bf.key, keylen, padded); |
| 231 | memset(context->u.bf.iv, 0, 8); |
| 232 | break; |
| 233 | |
| 234 | default: |
| 235 | fatal("cipher_set_key: unknown cipher: %d", cipher); |
| 236 | } |
| 237 | memset(padded, 0, sizeof(padded)); |
| 238 | } |
| 239 | |
| 240 | /* Encrypts data using the cipher. */ |
| 241 | |
| 242 | void cipher_encrypt(CipherContext *context, unsigned char *dest, |
| 243 | const unsigned char *src, unsigned int len) |
| 244 | { |
| 245 | assert((len & 7) == 0); |
| 246 | |
| 247 | switch (context->type) |
| 248 | { |
| 249 | case SSH_CIPHER_NONE: |
| 250 | memcpy(dest, src, len); |
| 251 | break; |
| 252 | |
| 253 | case SSH_CIPHER_3DES: |
| 254 | SSH_3CBC_ENCRYPT(context->u.des3.key1, |
| 255 | context->u.des3.key2, &context->u.des3.iv2, |
| 256 | context->u.des3.key3, &context->u.des3.iv3, |
| 257 | dest, (void*)src, len); |
| 258 | break; |
| 259 | |
| 260 | case SSH_CIPHER_BLOWFISH: |
| 261 | swap_bytes(src, dest, len); |
| 262 | BF_cbc_encrypt(dest, dest, len, |
| 263 | &context->u.bf.key, context->u.bf.iv, BF_ENCRYPT); |
| 264 | swap_bytes(dest, dest, len); |
| 265 | break; |
| 266 | |
| 267 | default: |
| 268 | fatal("cipher_encrypt: unknown cipher: %d", context->type); |
| 269 | } |
| 270 | } |
| 271 | |
| 272 | /* Decrypts data using the cipher. */ |
| 273 | |
| 274 | void cipher_decrypt(CipherContext *context, unsigned char *dest, |
| 275 | const unsigned char *src, unsigned int len) |
| 276 | { |
| 277 | assert((len & 7) == 0); |
| 278 | |
| 279 | switch (context->type) |
| 280 | { |
| 281 | case SSH_CIPHER_NONE: |
| 282 | memcpy(dest, src, len); |
| 283 | break; |
| 284 | |
| 285 | case SSH_CIPHER_3DES: |
| 286 | /* CRC-32 attack? */ |
| 287 | SSH_3CBC_DECRYPT(context->u.des3.key1, |
| 288 | context->u.des3.key2, &context->u.des3.iv2, |
| 289 | context->u.des3.key3, &context->u.des3.iv3, |
| 290 | dest, (void*)src, len); |
| 291 | break; |
| 292 | |
| 293 | case SSH_CIPHER_BLOWFISH: |
| 294 | detect_cbc_attack(src, len); |
| 295 | swap_bytes(src, dest, len); |
| 296 | BF_cbc_encrypt((void*)dest, dest, len, |
| 297 | &context->u.bf.key, context->u.bf.iv, BF_DECRYPT); |
| 298 | swap_bytes(dest, dest, len); |
| 299 | break; |
| 300 | |
| 301 | default: |
| 302 | fatal("cipher_decrypt: unknown cipher: %d", context->type); |
| 303 | } |
| 304 | } |