/* Decoder for password encoding of Cisco VPN client. Copyright (C) 2005 Maurice Massar Thanks to HAL-9000@evilscientists.de for decoding and posting the algorithm!This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ /* Requires libgcrypt version 1.1.90 or newer Compile with: gcc -Wall -o cisco-decrypt cisco-decrypt.c $(libgcrypt-config --libs --cflags) Usage: ./cisco-decrypt DEADBEEF...012345678 424242...7261 */ #include <stdio.h> #include <stdlib.h> #include <gcrypt.h> #include <errno.h> int hex2bin_c(unsigned int c) { if ((c >= '0')&&(c <= '9')) return c - '0'; if ((c >= 'A')&&(c <= 'F')) return c - 'A' + 10; if ((c >= 'a')&&(c <= 'f')) return c - 'a' + 10; return -1; } int hex2bin(const char *str, char **bin, int *len) { char *p; int i, l; if (!bin) return EINVAL; for (i = 0; str[i] != '\0'; i++) if (hex2bin_c(str[i]) == -1) return EINVAL; l = i; if ((l & 1) != 0) return EINVAL; l /= 2; p = malloc(l); if (p == NULL) return ENOMEM; for (i = 0; i < l; i++) p[i] = hex2bin_c(str[i*2]) << 4 | hex2bin_c(str[i*2+1]); *bin = p; if (len) *len = l; return 0; } int c_decrypt(char *ct, int len, char **resp, char *reslenp) { const char *h1 = ct; const char *h4 = ct + 20; const char *enc = ct + 40; char ht[20], h2[20], h3[20], key[24]; const char *iv = h1; char *res; gcry_cipher_hd_t ctx; int reslen; if (len < 48) return 0; len -= 40; memcpy(ht, h1, 20); ht[19]++; gcry_md_hash_buffer(GCRY_MD_SHA1, h2, ht, 20); ht[19] += 2; gcry_md_hash_buffer(GCRY_MD_SHA1, h3, ht, 20); memcpy(key, h2, 20); memcpy(key+20, h3, 4); /* who cares about parity anyway? */ gcry_md_hash_buffer(GCRY_MD_SHA1, ht, enc, len); if (memcmp(h4, ht, 20) != 0) return -1; res = malloc(len); if (res == NULL) return -1; gcry_cipher_open(&ctx, GCRY_CIPHER_3DES, GCRY_CIPHER_MODE_CBC, 0); gcry_cipher_setkey(ctx, key, 24); gcry_cipher_setiv(ctx, iv, 8); gcry_cipher_decrypt(ctx, (unsigned char *)res, len, (unsigned char *)enc, len); gcry_cipher_close(ctx); reslen = len - res[len-1]; res[reslen] = '\0'; if (resp) *resp = res; if (reslenp) *reslenp = reslen; return 0; } int main(int argc, char *argv[]) { int i, len, ret = 0; char *bin, *pw; gcry_check_version(NULL); for (i = 1; i < argc; i++) { ret = hex2bin(argv[i], &bin, &len); if (ret != 0) { perror("decoding input"); continue; } ret = c_decrypt(bin, len, &pw, NULL); free(bin); if (ret != 0) { perror("decrypting input"); continue; } printf("%s\n", pw); free(pw); } exit(ret != 0); } Download: cisco-decrypt