crypt_common.c

   1 /*
   2  * Copyright (C) 2005-2012 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file crypt_common.c Crypto functions independent of openssl/libgcrypt. */
   8
   9 #include <regex.h>
  10
  11 #include "para.h"
  12 #include "error.h"
  13 #include "string.h"
  14 #include "crypt_backend.h"
  15 #include "crypt.h"
  16
  17 /** If the key begins with this text, we treat it as an ssh key. */
  18 #define KEY_TYPE_TXT "ssh-rsa"
  19
  20 /**
  21  * Check if given buffer starts with a ssh rsa key signature.
  22  *
  23  * \param data The buffer.
  24  * \param size Number of data bytes.
  25  *
  26  * \return Number of header bytes to be skipped on success, zero if
  27  * ssh rsa signature was not found.
  28  */
  29 size_t is_ssh_rsa_key(char *data, size_t size)
  30 {
  31         char *cp;
  32
  33         if (size < strlen(KEY_TYPE_TXT) + 2)
  34                 return 0;
  35         cp = memchr(data, ' ', size);
  36         if (cp == NULL)
  37                 return 0;
  38         if (strncmp(KEY_TYPE_TXT, data, strlen(KEY_TYPE_TXT)))
  39                 return 0;
  40         cp++;
  41         if (cp >= data + size)
  42                 return 0;
  43         if (*cp == '\0')
  44                 return 0;
  45         return cp - data;
  46 }
  47
  48 /*
  49  * This base64/uudecode stuff below is taken from openssh-5.2p1, Copyright (c)
  50  * 1996 by Internet Software Consortium.  Portions Copyright (c) 1995 by
  51  * International Business Machines, Inc.
  52  */
  53
  54 static const char Base64[] =
  55         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  56 static const char Pad64 = '=';
  57
  58 /**
  59  * base64-decode a buffer.
  60  *
  61  * \param src The buffer to decode.
  62  * \param target Result is stored here.
  63  * \param targsize Number of bytes of \a target.
  64  *
  65  * Skips all whitespace anywhere. Converts characters, four at a time, starting
  66  * at (or after) src from base - 64 numbers into three 8 bit bytes in the
  67  * target area.
  68  *
  69  * \return The number of data bytes stored at the target, -E_BASE64 on errors.
  70  */
  71 int base64_decode(char const *src, unsigned char *target, size_t targsize)
  72 {
  73         unsigned int tarindex, state;
  74         int ch;
  75         char *pos;
  76
  77         state = 0;
  78         tarindex = 0;
  79
  80         while ((ch = *src++) != '\0') {
  81                 if (para_isspace(ch)) /* Skip whitespace anywhere. */
  82                         continue;
  83
  84                 if (ch == Pad64)
  85                         break;
  86
  87                 pos = strchr(Base64, ch);
  88                 if (pos == NULL) /* A non-base64 character. */
  89                         return -E_BASE64;
  90
  91                 switch (state) {
  92                 case 0:
  93                         if (target) {
  94                                 if (tarindex >= targsize)
  95                                         return -E_BASE64;
  96                                 target[tarindex] = (pos - Base64) << 2;
  97                         }
  98                         state = 1;
  99                         break;
 100                 case 1:
 101                         if (target) {
 102                                 if (tarindex + 1 >= targsize)
 103                                         return -E_BASE64;
 104                                 target[tarindex]   |=  (pos - Base64) >> 4;
 105                                 target[tarindex+1]  = ((pos - Base64) & 0x0f)
 106                                                         << 4 ;
 107                         }
 108                         tarindex++;
 109                         state = 2;
 110                         break;
 111                 case 2:
 112                         if (target) {
 113                                 if (tarindex + 1 >= targsize)
 114                                         return -E_BASE64;
 115                                 target[tarindex]   |=  (pos - Base64) >> 2;
 116                                 target[tarindex+1]  = ((pos - Base64) & 0x03)
 117                                                         << 6;
 118                         }
 119                         tarindex++;
 120                         state = 3;
 121                         break;
 122                 case 3:
 123                         if (target) {
 124                                 if (tarindex >= targsize)
 125                                         return -E_BASE64;
 126                                 target[tarindex] |= (pos - Base64);
 127                         }
 128                         tarindex++;
 129                         state = 0;
 130                         break;
 131                 }
 132         }
 133
 134         /*
 135          * We are done decoding Base-64 chars.  Let's see if we ended
 136          * on a byte boundary, and/or with erroneous trailing characters.
 137          */
 138
 139         if (ch == Pad64) {              /* We got a pad char. */
 140                 ch = *src++;            /* Skip it, get next. */
 141                 switch (state) {
 142                 case 0:         /* Invalid = in first position */
 143                 case 1:         /* Invalid = in second position */
 144                         return -E_BASE64;
 145
 146                 case 2:         /* Valid, means one byte of info */
 147                         /* Skip any number of spaces. */
 148                         for (; ch != '\0'; ch = *src++)
 149                                 if (!isspace(ch))
 150                                         break;
 151                         /* Make sure there is another trailing = sign. */
 152                         if (ch != Pad64)
 153                                 return -E_BASE64;
 154                         ch = *src++;            /* Skip the = */
 155                         /* Fall through to "single trailing =" case. */
 156                         /* FALLTHROUGH */
 157
 158                 case 3:         /* Valid, means two bytes of info */
 159                         /*
 160                          * We know this char is an =.  Is there anything but
 161                          * whitespace after it?
 162                          */
 163                         for (; ch != '\0'; ch = *src++)
 164                                 if (!isspace(ch))
 165                                         return -E_BASE64;
 166
 167                         /*
 168                          * Now make sure for cases 2 and 3 that the "extra"
 169                          * bits that slopped past the last full byte were
 170                          * zeros.  If we don't check them, they become a
 171                          * subliminal channel.
 172                          */
 173                         if (target && target[tarindex] != 0)
 174                                 return -E_BASE64;
 175                 }
 176         } else {
 177                 /*
 178                  * We ended by seeing the end of the string.  Make sure we
 179                  * have no partial bytes lying around.
 180                  */
 181                 if (state != 0)
 182                         return -E_BASE64;
 183         }
 184
 185         return tarindex;
 186 }
 187
 188 /**
 189  * uudecode a buffer.
 190  *
 191  * \param src The buffer to decode.
 192  * \param target Result buffer.
 193  * \param targsize The length of \a target in bytes.
 194  *
 195  * This is just a simple wrapper for base64_decode() which strips whitespace.
 196  *
 197  * \return The return value of the underlying call to base64_decode().
 198  */
 199 int uudecode(const char *src, unsigned char *target, size_t targsize)
 200 {
 201         int len;
 202         char *encoded, *p;
 203
 204         /* copy the 'readonly' source */
 205         encoded = para_strdup(src);
 206         /* skip whitespace and data */
 207         for (p = encoded; *p == ' ' || *p == '\t'; p++)
 208                 ;
 209         for (; *p != '\0' && *p != ' ' && *p != '\t'; p++)
 210                 ;
 211         /* and remove trailing whitespace because base64_decode needs this */
 212         *p = '\0';
 213         len = base64_decode(encoded, target, targsize);
 214         free(encoded);
 215         return len;
 216 }
 217
 218 /**
 219  * Read a 4-byte number from a buffer in big-endian format.
 220  *
 221  * \param vp The buffer.
 222  *
 223  * The byte-order of the buffer is expected to be big-endian, unlike read_u32()
 224  * of portable_io.h which expects little endian.
 225  *
 226  * \return The 32 bit number given by \a vp.
 227  */
 228 uint32_t read_ssh_u32(const void *vp)
 229 {
 230         const unsigned char *p = (const unsigned char *)vp;
 231         uint32_t v;
 232
 233         v  = (uint32_t)p[0] << 24;
 234         v |= (uint32_t)p[1] << 16;
 235         v |= (uint32_t)p[2] << 8;
 236         v |= (uint32_t)p[3];
 237
 238         return v;
 239 }
 240
 241 /**
 242  * Sanity checks for the header of an ssh key.
 243  *
 244  * \param blob The buffer.
 245  * \param blen The number of bytes of \a blob.
 246  *
 247  * This performs some checks to make sure we really have an ssh key. It also
 248  * computes the offset in bytes of the start of the key values (modulus,
 249  * exponent..).
 250  *
 251  * \return The number of bytes to skip until the start of the first encoded
 252  * number (usually 11).
 253  */
 254 int check_ssh_key_header(const unsigned char *blob, int blen)
 255 {
 256         const unsigned char *p = blob, *end = blob + blen;
 257         uint32_t rlen;
 258
 259         if (p + 4 > end)
 260                 return -E_SSH_KEY_HEADER;
 261         rlen = read_ssh_u32(p);
 262         p += 4;
 263         if (p + rlen < p)
 264                 return -E_SSH_KEY_HEADER;
 265         if (p + rlen > end)
 266                 return -E_SSH_KEY_HEADER;
 267         if (rlen < strlen(KEY_TYPE_TXT))
 268                 return -E_SSH_KEY_HEADER;
 269         PARA_DEBUG_LOG("type: %s, rlen: %d\n", p, rlen);
 270         if (strncmp((char *)p, KEY_TYPE_TXT, strlen(KEY_TYPE_TXT)))
 271                 return -E_SSH_KEY_HEADER;
 272         return 4 + rlen;
 273 }
 274
 275 /**
 276  * Check existence and permissions of a key file.
 277  *
 278  * \param file The path of the key file.
 279  * \param private_key Whether this is a private key.
 280  *
 281  * This checks whether the file exists. If it is a private key, we additionally
 282  * check that the permissions are restrictive enough. It is considered an error
 283  * if we own the file and it is readable for others.
 284  *
 285  * \return Standard.
 286  */
 287 int check_key_file(const char *file, bool private_key)
 288 {
 289         struct stat st;
 290
 291         if (stat(file, &st) != 0)
 292                 return -ERRNO_TO_PARA_ERROR(errno);
 293         if (!private_key)
 294                 return 0;
 295         if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0)
 296                 return -E_KEY_PERM;
 297         return 1;
 298 }
 299
 300 void hash_to_asc(unsigned char *hash, char *asc)
 301 {
 302         int i;
 303         const char hexchar[] = "0123456789abcdef";
 304
 305         for (i = 0; i < HASH_SIZE; i++) {
 306                 asc[2 * i] = hexchar[hash[i] >> 4];
 307                 asc[2 * i + 1] = hexchar[hash[i] & 0xf];
 308         }
 309         asc[2 * HASH_SIZE] = '\0';
 310 }
 311
 312 int hash_compare(unsigned char *h1, unsigned char *h2)
 313 {
 314         int i;
 315
 316         for (i = 0; i < HASH_SIZE; i++) {
 317                 if (h1[i] < h2[i])
 318                         return -1;
 319                 if (h1[i] > h2[i])
 320                         return 1;
 321         }
 322         return 0;
 323 }
 324
 325 int sc_recv_buffer(struct stream_cipher_context *scc, char *buf, size_t size)
 326 {
 327         int n;
 328
 329         assert(size);
 330         n = sc_recv_bin_buffer(scc, buf, size - 1);
 331         if (n >= 0)
 332                 buf[n] = '\0';
 333         else
 334                 *buf = '\0';
 335         return n;
 336 }
 337
 338 int sc_send_buffer(struct stream_cipher_context *scc, char *buf)
 339 {
 340         return sc_send_bin_buffer(scc, buf, strlen(buf));
 341 }
 342
 343 __printf_2_3 int sc_send_va_buffer(struct stream_cipher_context *scc,
 344                 const char *fmt, ...)
 345 {
 346         char *msg;
 347         int ret;
 348
 349         PARA_VSPRINTF(fmt, msg);
 350         ret = sc_send_buffer(scc, msg);
 351         free(msg);
 352         return ret;
 353 }