crypt_common.c

   1 /*
   2  * Copyright (C) 2005-2014 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.h"
  15 #include "crypt_backend.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 (tarindex >= targsize)
  94                                 return -E_BASE64;
  95                         target[tarindex] = (pos - Base64) << 2;
  96                         state = 1;
  97                         break;
  98                 case 1:
  99                         if (tarindex + 1 >= targsize)
 100                                 return -E_BASE64;
 101                         target[tarindex] |= (pos - Base64) >> 4;
 102                         target[tarindex + 1] = ((pos - Base64) & 0x0f) << 4;
 103                         tarindex++;
 104                         state = 2;
 105                         break;
 106                 case 2:
 107                         if (tarindex + 1 >= targsize)
 108                                 return -E_BASE64;
 109                         target[tarindex] |= (pos - Base64) >> 2;
 110                         target[tarindex + 1] = ((pos - Base64) & 0x03) << 6;
 111                         tarindex++;
 112                         state = 3;
 113                         break;
 114                 case 3:
 115                         if (tarindex >= targsize)
 116                                 return -E_BASE64;
 117                         target[tarindex] |= pos - Base64;
 118                         tarindex++;
 119                         state = 0;
 120                         break;
 121                 }
 122         }
 123
 124         /*
 125          * We are done decoding Base-64 chars.  Let's see if we ended
 126          * on a byte boundary, and/or with erroneous trailing characters.
 127          */
 128
 129         if (ch == Pad64) {              /* We got a pad char. */
 130                 ch = *src++;            /* Skip it, get next. */
 131                 switch (state) {
 132                 case 0:         /* Invalid = in first position */
 133                 case 1:         /* Invalid = in second position */
 134                         return -E_BASE64;
 135
 136                 case 2:         /* Valid, means one byte of info */
 137                         /* Skip any number of spaces. */
 138                         for (; ch != '\0'; ch = *src++)
 139                                 if (!isspace(ch))
 140                                         break;
 141                         /* Make sure there is another trailing = sign. */
 142                         if (ch != Pad64)
 143                                 return -E_BASE64;
 144                         ch = *src++;            /* Skip the = */
 145                         /* Fall through to "single trailing =" case. */
 146                         /* FALLTHROUGH */
 147
 148                 case 3:         /* Valid, means two bytes of info */
 149                         /*
 150                          * We know this char is an =.  Is there anything but
 151                          * whitespace after it?
 152                          */
 153                         for (; ch != '\0'; ch = *src++)
 154                                 if (!isspace(ch))
 155                                         return -E_BASE64;
 156
 157                         /*
 158                          * Now make sure for cases 2 and 3 that the "extra"
 159                          * bits that slopped past the last full byte were
 160                          * zeros.  If we don't check them, they become a
 161                          * subliminal channel.
 162                          */
 163                         if (target[tarindex] != 0)
 164                                 return -E_BASE64;
 165                 }
 166         } else {
 167                 /*
 168                  * We ended by seeing the end of the string.  Make sure we
 169                  * have no partial bytes lying around.
 170                  */
 171                 if (state != 0)
 172                         return -E_BASE64;
 173         }
 174
 175         return tarindex;
 176 }
 177
 178 /**
 179  * uudecode a buffer.
 180  *
 181  * \param src The buffer to decode.
 182  * \param target Result buffer.
 183  * \param targsize The length of \a target in bytes.
 184  *
 185  * This is just a simple wrapper for base64_decode() which strips whitespace.
 186  *
 187  * \return The return value of the underlying call to base64_decode().
 188  */
 189 int uudecode(const char *src, unsigned char *target, size_t targsize)
 190 {
 191         int len;
 192         char *encoded, *p;
 193
 194         /* copy the 'readonly' source */
 195         encoded = para_strdup(src);
 196         /* skip whitespace and data */
 197         for (p = encoded; *p == ' ' || *p == '\t'; p++)
 198                 ;
 199         for (; *p != '\0' && *p != ' ' && *p != '\t'; p++)
 200                 ;
 201         /* and remove trailing whitespace because base64_decode needs this */
 202         *p = '\0';
 203         len = base64_decode(encoded, target, targsize);
 204         free(encoded);
 205         return len;
 206 }
 207
 208 /**
 209  * Read a 4-byte number from a buffer in big-endian format.
 210  *
 211  * \param vp The buffer.
 212  *
 213  * The byte-order of the buffer is expected to be big-endian, unlike read_u32()
 214  * of portable_io.h which expects little endian.
 215  *
 216  * \return The 32 bit number given by \a vp.
 217  */
 218 uint32_t read_ssh_u32(const void *vp)
 219 {
 220         const unsigned char *p = (const unsigned char *)vp;
 221         uint32_t v;
 222
 223         v  = (uint32_t)p[0] << 24;
 224         v |= (uint32_t)p[1] << 16;
 225         v |= (uint32_t)p[2] << 8;
 226         v |= (uint32_t)p[3];
 227
 228         return v;
 229 }
 230
 231 /**
 232  * Sanity checks for the header of an ssh key.
 233  *
 234  * \param blob The buffer.
 235  * \param blen The number of bytes of \a blob.
 236  *
 237  * This performs some checks to make sure we really have an ssh key. It also
 238  * computes the offset in bytes of the start of the key values (modulus,
 239  * exponent..).
 240  *
 241  * \return The number of bytes to skip until the start of the first encoded
 242  * number (usually 11).
 243  */
 244 int check_ssh_key_header(const unsigned char *blob, int blen)
 245 {
 246         const unsigned char *p = blob, *end = blob + blen;
 247         uint32_t rlen;
 248
 249         if (p + 4 > end)
 250                 return -E_SSH_KEY_HEADER;
 251         rlen = read_ssh_u32(p);
 252         p += 4;
 253         if (p + rlen < p)
 254                 return -E_SSH_KEY_HEADER;
 255         if (p + rlen > end)
 256                 return -E_SSH_KEY_HEADER;
 257         if (rlen < strlen(KEY_TYPE_TXT))
 258                 return -E_SSH_KEY_HEADER;
 259         PARA_DEBUG_LOG("type: %s, rlen: %d\n", p, rlen);
 260         if (strncmp((char *)p, KEY_TYPE_TXT, strlen(KEY_TYPE_TXT)))
 261                 return -E_SSH_KEY_HEADER;
 262         return 4 + rlen;
 263 }
 264
 265 /**
 266  * Check existence and permissions of a key file.
 267  *
 268  * \param file The path of the key file.
 269  * \param private_key Whether this is a private key.
 270  *
 271  * This checks whether the file exists. If it is a private key, we additionally
 272  * check that the permissions are restrictive enough. It is considered an error
 273  * if we own the file and it is readable for others.
 274  *
 275  * \return Standard.
 276  */
 277 int check_key_file(const char *file, bool private_key)
 278 {
 279         struct stat st;
 280
 281         if (stat(file, &st) != 0)
 282                 return -ERRNO_TO_PARA_ERROR(errno);
 283         if (!private_key)
 284                 return 0;
 285         if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0)
 286                 return -E_KEY_PERM;
 287         return 1;
 288 }
 289
 290 void hash_to_asc(unsigned char *hash, char *asc)
 291 {
 292         int i;
 293         const char hexchar[] = "0123456789abcdef";
 294
 295         for (i = 0; i < HASH_SIZE; i++) {
 296                 asc[2 * i] = hexchar[hash[i] >> 4];
 297                 asc[2 * i + 1] = hexchar[hash[i] & 0xf];
 298         }
 299         asc[2 * HASH_SIZE] = '\0';
 300 }
 301
 302 int hash_compare(unsigned char *h1, unsigned char *h2)
 303 {
 304         int i;
 305
 306         for (i = 0; i < HASH_SIZE; i++) {
 307                 if (h1[i] < h2[i])
 308                         return -1;
 309                 if (h1[i] > h2[i])
 310                         return 1;
 311         }
 312         return 0;
 313 }