Annotation of src/usr.bin/ssh/cipher.c, Revision 1.17
1.1 deraadt 1: /*
1.17 ! deraadt 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: */
1.1 deraadt 13:
14: #include "includes.h"
1.17 ! deraadt 15: RCSID("$Id: cipher.c,v 1.16 1999/11/23 22:25:53 markus Exp $");
1.1 deraadt 16:
17: #include "ssh.h"
18: #include "cipher.h"
1.8 deraadt 19:
1.12 deraadt 20: #include <ssl/md5.h>
1.1 deraadt 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,
1.16 markus 36: des_key_schedule ks2, des_cblock * iv2,
37: des_key_schedule ks3, des_cblock * iv3,
1.1 deraadt 38: void *dest, void *src,
39: unsigned int len)
40: {
1.16 markus 41: des_cblock iv1;
1.1 deraadt 42:
1.16 markus 43: memcpy(&iv1, iv2, 8);
1.1 deraadt 44:
1.16 markus 45: des_cbc_encrypt(src, dest, len, ks1, &iv1, DES_ENCRYPT);
46: memcpy(&iv1, dest + len - 8, 8);
1.1 deraadt 47:
1.16 markus 48: des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_DECRYPT);
49: memcpy(iv2, &iv1, 8); /* Note how iv1 == iv2 on entry and exit. */
1.1 deraadt 50:
1.16 markus 51: des_cbc_encrypt(dest, dest, len, ks3, iv3, DES_ENCRYPT);
52: memcpy(iv3, dest + len - 8, 8);
1.1 deraadt 53: }
54:
55: void
56: SSH_3CBC_DECRYPT(des_key_schedule ks1,
1.16 markus 57: des_key_schedule ks2, des_cblock * iv2,
58: des_key_schedule ks3, des_cblock * iv3,
1.1 deraadt 59: void *dest, void *src,
60: unsigned int len)
61: {
1.16 markus 62: des_cblock iv1;
1.1 deraadt 63:
1.16 markus 64: memcpy(&iv1, iv2, 8);
1.1 deraadt 65:
1.16 markus 66: des_cbc_encrypt(src, dest, len, ks3, iv3, DES_DECRYPT);
67: memcpy(iv3, src + len - 8, 8);
1.1 deraadt 68:
1.16 markus 69: des_cbc_encrypt(dest, dest, len, ks2, iv2, DES_ENCRYPT);
70: memcpy(iv2, dest + len - 8, 8);
1.1 deraadt 71:
1.16 markus 72: des_cbc_encrypt(dest, dest, len, ks1, &iv1, DES_DECRYPT);
73: /* memcpy(&iv1, iv2, 8); */
74: /* Note how iv1 == iv2 on entry and exit. */
1.1 deraadt 75: }
76:
77: /*
78: * SSH uses a variation on Blowfish, all bytes must be swapped before
79: * and after encryption/decryption. Thus the swap_bytes stuff (yuk).
80: */
1.16 markus 81: static void
1.1 deraadt 82: swap_bytes(const unsigned char *src, unsigned char *dst_, int n)
83: {
1.16 markus 84: /* dst must be properly aligned. */
85: u_int32_t *dst = (u_int32_t *) dst_;
86: union {
87: u_int32_t i;
88: char c[4];
89: } t;
90:
91: /* Process 8 bytes every lap. */
92: for (n = n / 8; n > 0; n--) {
93: t.c[3] = *src++;
94: t.c[2] = *src++;
95: t.c[1] = *src++;
96: t.c[0] = *src++;
97: *dst++ = t.i;
98:
99: t.c[3] = *src++;
100: t.c[2] = *src++;
101: t.c[1] = *src++;
102: t.c[0] = *src++;
103: *dst++ = t.i;
104: }
1.1 deraadt 105: }
106:
1.16 markus 107: void (*cipher_attack_detected) (const char *fmt,...) = fatal;
1.1 deraadt 108:
1.16 markus 109: static inline void
1.1 deraadt 110: detect_cbc_attack(const unsigned char *src,
111: unsigned int len)
112: {
1.16 markus 113: return;
114:
115: log("CRC-32 CBC insertion attack detected");
116: cipher_attack_detected("CRC-32 CBC insertion attack detected");
1.1 deraadt 117: }
118:
119: /* Names of all encryption algorithms. These must match the numbers defined
120: int cipher.h. */
121: static char *cipher_names[] =
1.4 provos 122: {
1.16 markus 123: "none",
124: "idea",
125: "des",
126: "3des",
127: "tss",
128: "rc4",
129: "blowfish"
1.1 deraadt 130: };
131:
132: /* Returns a bit mask indicating which ciphers are supported by this
133: implementation. The bit mask has the corresponding bit set of each
134: supported cipher. */
135:
1.16 markus 136: unsigned int
137: cipher_mask()
1.1 deraadt 138: {
1.16 markus 139: unsigned int mask = 0;
140: mask |= 1 << SSH_CIPHER_3DES; /* Mandatory */
141: mask |= 1 << SSH_CIPHER_BLOWFISH;
142: return mask;
1.1 deraadt 143: }
144:
145: /* Returns the name of the cipher. */
146:
1.16 markus 147: const char *
148: cipher_name(int cipher)
1.1 deraadt 149: {
1.16 markus 150: if (cipher < 0 || cipher >= sizeof(cipher_names) / sizeof(cipher_names[0]) ||
151: cipher_names[cipher] == NULL)
152: fatal("cipher_name: bad cipher number: %d", cipher);
153: return cipher_names[cipher];
1.1 deraadt 154: }
155:
156: /* Parses the name of the cipher. Returns the number of the corresponding
157: cipher, or -1 on error. */
158:
1.4 provos 159: int
160: cipher_number(const char *name)
1.1 deraadt 161: {
1.16 markus 162: int i;
163: for (i = 0; i < sizeof(cipher_names) / sizeof(cipher_names[0]); i++)
164: if (strcmp(cipher_names[i], name) == 0 &&
165: (cipher_mask() & (1 << i)))
166: return i;
167: return -1;
1.1 deraadt 168: }
169:
170: /* Selects the cipher, and keys if by computing the MD5 checksum of the
171: passphrase and using the resulting 16 bytes as the key. */
172:
1.16 markus 173: void
174: cipher_set_key_string(CipherContext *context, int cipher,
175: const char *passphrase, int for_encryption)
1.1 deraadt 176: {
1.16 markus 177: MD5_CTX md;
178: unsigned char digest[16];
179:
180: MD5_Init(&md);
181: MD5_Update(&md, (const unsigned char *) passphrase, strlen(passphrase));
182: MD5_Final(digest, &md);
183:
184: cipher_set_key(context, cipher, digest, 16, for_encryption);
185:
186: memset(digest, 0, sizeof(digest));
187: memset(&md, 0, sizeof(md));
1.1 deraadt 188: }
189:
190: /* Selects the cipher to use and sets the key. */
191:
1.16 markus 192: void
193: 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
202: below does 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: case SSH_CIPHER_NONE:
209: /* Has to stay for authfile saving of private key with
210: no passphrase */
211: break;
212:
213: case SSH_CIPHER_3DES:
214: /* Note: the least significant bit of each byte of key is
215: parity, and must be ignored by the implementation. 16
216: bytes of key are used (first and last keys are the
217: same). */
218: if (keylen < 16)
219: error("Key length %d is insufficient for 3DES.", keylen);
220: des_set_key((void *) padded, context->u.des3.key1);
221: des_set_key((void *) (padded + 8), context->u.des3.key2);
222: if (keylen <= 16)
223: des_set_key((void *) padded, context->u.des3.key3);
224: else
225: des_set_key((void *) (padded + 16), context->u.des3.key3);
226: memset(context->u.des3.iv2, 0, sizeof(context->u.des3.iv2));
227: memset(context->u.des3.iv3, 0, sizeof(context->u.des3.iv3));
228: break;
229:
230: case SSH_CIPHER_BLOWFISH:
231: BF_set_key(&context->u.bf.key, keylen, padded);
232: memset(context->u.bf.iv, 0, 8);
233: break;
234:
235: default:
236: fatal("cipher_set_key: unknown cipher: %s", cipher_name(cipher));
237: }
238: memset(padded, 0, sizeof(padded));
1.1 deraadt 239: }
240:
241: /* Encrypts data using the cipher. */
242:
1.16 markus 243: void
244: cipher_encrypt(CipherContext *context, unsigned char *dest,
245: const unsigned char *src, unsigned int len)
246: {
247: if ((len & 7) != 0)
248: fatal("cipher_encrypt: bad plaintext length %d", len);
249:
250: switch (context->type) {
251: case SSH_CIPHER_NONE:
252: memcpy(dest, src, len);
253: break;
254:
255: case SSH_CIPHER_3DES:
256: SSH_3CBC_ENCRYPT(context->u.des3.key1,
257: context->u.des3.key2, &context->u.des3.iv2,
258: context->u.des3.key3, &context->u.des3.iv3,
259: dest, (void *) src, len);
260: break;
261:
262: case SSH_CIPHER_BLOWFISH:
263: swap_bytes(src, dest, len);
264: BF_cbc_encrypt(dest, dest, len,
265: &context->u.bf.key, context->u.bf.iv,
266: BF_ENCRYPT);
267: swap_bytes(dest, dest, len);
268: break;
269:
270: default:
271: fatal("cipher_encrypt: unknown cipher: %s", cipher_name(context->type));
272: }
273: }
1.1 deraadt 274:
275: /* Decrypts data using the cipher. */
276:
1.16 markus 277: void
278: cipher_decrypt(CipherContext *context, unsigned char *dest,
279: const unsigned char *src, unsigned int len)
280: {
281: if ((len & 7) != 0)
282: fatal("cipher_decrypt: bad ciphertext length %d", len);
283:
284: switch (context->type) {
285: case SSH_CIPHER_NONE:
286: memcpy(dest, src, len);
287: break;
288:
289: case SSH_CIPHER_3DES:
290: /* CRC-32 attack? */
291: SSH_3CBC_DECRYPT(context->u.des3.key1,
292: context->u.des3.key2, &context->u.des3.iv2,
293: context->u.des3.key3, &context->u.des3.iv3,
294: dest, (void *) src, len);
295: break;
296:
297: case SSH_CIPHER_BLOWFISH:
298: detect_cbc_attack(src, len);
299: swap_bytes(src, dest, len);
300: BF_cbc_encrypt((void *) dest, dest, len,
301: &context->u.bf.key, context->u.bf.iv,
302: BF_DECRYPT);
303: swap_bytes(dest, dest, len);
304: break;
305:
306: default:
307: fatal("cipher_decrypt: unknown cipher: %s", cipher_name(context->type));
308: }
1.1 deraadt 309: }
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