crypt_common.c

   1 /* Copyright (C) 2005 Andre Noll <maan@tuebingen.mpg.de>, see file COPYING. */
   2
   3 /** \file crypt_common.c Crypto functions independent of openssl/libgcrypt. */
   4
   5 #include <regex.h>
   6
   7 #include "para.h"
   8 #include "error.h"
   9 #include "string.h"
  10 #include "crypt.h"
  11 #include "crypt_backend.h"
  12 #include "portable_io.h"
  13 #include "fd.h"
  14 #include "base64.h"
  15
  16 /** If the key begins with this text, we treat it as an ssh key. */
  17 #define KEY_TYPE_TXT "ssh-rsa"
  18
  19 /*
  20  * Check if the given buffer starts with an ssh rsa key signature.
  21  *
  22  * Returns number of header bytes to be skipped on success, zero if no ssh rsa
  23  * signature was found.
  24  */
  25 static size_t is_ssh_rsa_key(char *data, size_t size)
  26 {
  27         char *cp;
  28
  29         if (size < strlen(KEY_TYPE_TXT) + 2)
  30                 return 0;
  31         cp = memchr(data, ' ', size);
  32         if (cp == NULL)
  33                 return 0;
  34         if (strncmp(KEY_TYPE_TXT, data, strlen(KEY_TYPE_TXT)))
  35                 return 0;
  36         cp++;
  37         if (cp >= data + size)
  38                 return 0;
  39         if (*cp == '\0')
  40                 return 0;
  41         return cp - data;
  42 }
  43
  44 /*
  45  * Perform some sanity checks on the decoded ssh key.
  46  *
  47  * This function returns the size of the header. Usually, the header is 11
  48  * bytes long: four bytes for the length field, and the string "ssh-rsa".
  49  */
  50 static int check_ssh_key_header(const unsigned char *blob, int blen)
  51 {
  52         const unsigned char *p = blob, *end = blob + blen;
  53         uint32_t rlen;
  54
  55         if (p + 4 > end)
  56                 return -E_SSH_KEY_HEADER;
  57         rlen = read_u32_be(p);
  58         p += 4;
  59         if (p + rlen < p)
  60                 return -E_SSH_KEY_HEADER;
  61         if (p + rlen > end)
  62                 return -E_SSH_KEY_HEADER;
  63         if (rlen < strlen(KEY_TYPE_TXT))
  64                 return -E_SSH_KEY_HEADER;
  65         PARA_DEBUG_LOG("type: %s, rlen: %u\n", p, rlen);
  66         if (strncmp((char *)p, KEY_TYPE_TXT, strlen(KEY_TYPE_TXT)))
  67                 return -E_SSH_KEY_HEADER;
  68         return 4 + rlen;
  69 }
  70
  71 /**
  72  * Perform sanity checks and base64-decode an ssh-rsa key.
  73  *
  74  * \param filename The public key file (usually id_rsa.pub).
  75  * \param blob Pointer to base64-decoded blob is returned here.
  76  * \param decoded_size The size of the decoded blob.
  77  *
  78  * The memory pointed at by the returned blob pointer has to be freed by the
  79  * caller.
  80  *
  81  * \return On success, the offset in bytes of the start of the key values
  82  * (modulus, exponent..). This is the number of bytes to skip from the blob
  83  * until the start of the first encoded number. On failure, a negative error
  84  * code is returned.
  85  *
  86  * \sa \ref uudecode().
  87  */
  88 int decode_public_key(const char *filename, unsigned char **blob,
  89                 size_t *decoded_size)
  90 {
  91         int ret, ret2;
  92         void *map;
  93         size_t map_size;
  94
  95         ret = mmap_full_file(filename, O_RDONLY, &map, &map_size, NULL);
  96         if (ret < 0)
  97                 return ret;
  98         ret = is_ssh_rsa_key(map, map_size);
  99         if (ret == 0) {
 100                 ret = -E_SSH_PARSE;
 101                 goto unmap;
 102         }
 103         ret = uudecode(map + ret, map_size - ret, (char **)blob, decoded_size);
 104         if (ret < 0)
 105                 goto unmap;
 106         ret = check_ssh_key_header(*blob, *decoded_size);
 107         if (ret < 0)
 108                 goto unmap;
 109 unmap:
 110         ret2 = para_munmap(map, map_size);
 111         if (ret >= 0 && ret2 < 0)
 112                 ret = ret2;
 113         return ret;
 114 }
 115
 116 /**
 117  * Check existence and permissions of a private key file.
 118  *
 119  * \param file The path of the key file.
 120  *
 121  * This checks whether the file exists and its permissions are restrictive
 122  * enough. It is considered an error if we own the file and it is readable for
 123  * others.
 124  *
 125  * \return Standard.
 126  */
 127 int check_private_key_file(const char *file)
 128 {
 129         struct stat st;
 130
 131         if (stat(file, &st) != 0)
 132                 return -ERRNO_TO_PARA_ERROR(errno);
 133         if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0)
 134                 return -E_KEY_PERM;
 135         return 1;
 136 }
 137
 138 void hash_to_asc(const unsigned char *hash, char *asc)
 139 {
 140         int i;
 141         const char hexchar[] = "0123456789abcdef";
 142
 143         for (i = 0; i < HASH_SIZE; i++) {
 144                 asc[2 * i] = hexchar[hash[i] >> 4];
 145                 asc[2 * i + 1] = hexchar[hash[i] & 0xf];
 146         }
 147         asc[2 * HASH_SIZE] = '\0';
 148 }
 149
 150 int hash_compare(const unsigned char *h1, const unsigned char *h2)
 151 {
 152         int i;
 153
 154         for (i = 0; i < HASH_SIZE; i++) {
 155                 if (h1[i] < h2[i])
 156                         return -1;
 157                 if (h1[i] > h2[i])
 158                         return 1;
 159         }
 160         return 0;
 161 }
 162
 163 /**
 164  * Check header of an openssh private key and compute bignum offset.
 165  *
 166  * \param data The base64-decoded key.
 167  * \param len The size of the decoded key.
 168  *
 169  * Several assumptions are made about the key. Most notably, we only support
 170  * single unencrypted keys without comments.
 171  *
 172  * \return The offset at which the first bignum of the private key (the public
 173  * exponent n) starts. Negative error code on failure.
 174  */
 175 int find_openssh_bignum_offset(const unsigned char *data, int len)
 176 {
 177         /*
 178          * Unencrypted keys without comments always start with the below byte
 179          * sequence. See PROTOCOL.key of the openssh package.
 180          */
 181         static const unsigned char valid_openssh_header[] = {
 182                 /* string "openssh-key-v1" */
 183                 0x6f, 0x70, 0x65, 0x6e, 0x73, 0x73, 0x68, 0x2d, 0x6b, 0x65,
 184                         0x79, 0x2d, 0x76, 0x31,
 185                 /* length of the cipher name */
 186                 0x00, 0x00, 0x00, 0x00, 0x04,
 187                 /* cipher name: "none" */
 188                 0x6e, 0x6f, 0x6e, 0x65,
 189                 /* length of the kdfname (only used for encrypted keys) */
 190                 0x00, 0x00, 0x00, 0x04,
 191                 /* kdfname: "none" */
 192                 0x6e, 0x6f, 0x6e, 0x65,
 193                 /* length of kdfoptions */
 194                 0x00, 0x00, 0x00, 0x00,
 195                 /* number of keys */
 196                 0x00, 0x00, 0x00, 0x01,
 197         };
 198         uint32_t val;
 199         const unsigned char *p, *end = data + len;
 200
 201         if (len <= sizeof(valid_openssh_header) + 4)
 202                 return -E_OPENSSH_PARSE;
 203         if (memcmp(data, valid_openssh_header, sizeof(valid_openssh_header)))
 204                 return -E_OPENSSH_PARSE;
 205         p = data + sizeof(valid_openssh_header);
 206         /* length of public key */
 207         val = read_u32_be(p);
 208         if (val > end - p - 4)
 209                 return -E_OPENSSH_PARSE;
 210         p += val + 4;
 211         /* length of private key */
 212         val = read_u32_be(p);
 213         if (val > end - p - 4)
 214                 return -E_OPENSSH_PARSE;
 215         p += 4;
 216         /* two equal random integers ("checkint") */
 217         if (p + 8 > end)
 218                 return -E_OPENSSH_PARSE;
 219         if (read_u32_be(p) != read_u32_be(p + 4))
 220                 return -E_OPENSSH_PARSE;
 221         p += 8;
 222         /* length of name of key type "ssh-rsa" */
 223         if (p + 11 > end)
 224                 return -E_OPENSSH_PARSE;
 225         if (read_u32_be(p) != 7)
 226                 return -E_OPENSSH_PARSE;
 227         if (memcmp(p + 4, "ssh-rsa", 7))
 228                 return -E_OPENSSH_PARSE;
 229         p += 11;
 230         return p - data;
 231 }
 232
 233 /** Private PEM keys (legacy format) start with this header. */
 234 #define PRIVATE_PEM_KEY_HEADER "-----BEGIN RSA PRIVATE KEY-----"
 235 /** Private OPENSSH keys (RFC4716) start with this header. */
 236 #define PRIVATE_OPENSSH_KEY_HEADER "-----BEGIN OPENSSH PRIVATE KEY-----"
 237 /** Private PEM keys (legacy format) end with this footer. */
 238 #define PRIVATE_PEM_KEY_FOOTER "-----END RSA PRIVATE KEY-----"
 239 /** Private OPENSSH keys (RFC4716) end with this footer. */
 240 #define PRIVATE_OPENSSH_KEY_FOOTER "-----END OPENSSH PRIVATE KEY-----"
 241
 242 /**
 243  * Decode an openssh-v1 (aka RFC4716) or PEM (aka ASN.1) private key.
 244  *
 245  * \param key_file The private key file (usually id_rsa).
 246  * \param result Pointer to base64-decoded blob is returned here.
 247  * \param blob_size The size of the decoded blob.
 248  *
 249  * This only checks header and footer and base64-decodes the part in between.
 250  * No attempt to read the decoded part is made.
 251  *
 252  * \return Negative on errors, PKT_PEM or PKT_OPENSSH on success, indicating
 253  * the type of key.
 254  */
 255 int decode_private_key(const char *key_file, unsigned char **result,
 256                 size_t *blob_size)
 257 {
 258         int ret, ret2, i, j, key_type;
 259         void *map;
 260         size_t map_size, key_size;
 261         unsigned char *blob = NULL;
 262         char *begin, *footer, *key;
 263
 264         ret = mmap_full_file(key_file, O_RDONLY, &map, &map_size, NULL);
 265         if (ret < 0)
 266                 goto out;
 267         ret = -E_KEY_MARKER;
 268         if (strncmp(map, PRIVATE_PEM_KEY_HEADER,
 269                         strlen(PRIVATE_PEM_KEY_HEADER)) == 0) {
 270                 key_type = PKT_PEM;
 271                 begin = map + strlen(PRIVATE_PEM_KEY_HEADER);
 272                 footer = strstr(map, PRIVATE_PEM_KEY_FOOTER);
 273                 PARA_INFO_LOG("detected legacy PEM key %s\n", key_file);
 274         } else if (strncmp(map, PRIVATE_OPENSSH_KEY_HEADER,
 275                         strlen(PRIVATE_OPENSSH_KEY_HEADER)) == 0) {
 276                 key_type = PKT_OPENSSH;
 277                 begin = map + strlen(PRIVATE_OPENSSH_KEY_HEADER);
 278                 footer = strstr(map, PRIVATE_OPENSSH_KEY_FOOTER);
 279                 PARA_INFO_LOG("detected openssh key %s\n", key_file);
 280         } else
 281                 goto unmap;
 282         if (!footer)
 283                 goto unmap;
 284         /* skip whitespace at the beginning */
 285         for (; begin < footer; begin++) {
 286                 if (para_isspace(*begin))
 287                         continue;
 288                 break;
 289         }
 290         ret = -E_KEY_MARKER;
 291         if (begin >= footer)
 292                 goto unmap;
 293
 294         key_size = footer - begin;
 295         key = para_malloc(key_size + 1);
 296         for (i = 0, j = 0; begin + i < footer; i++) {
 297                 if (para_isspace(begin[i]))
 298                         continue;
 299                 key[j++] = begin[i];
 300         }
 301         key[j] = '\0';
 302         ret = base64_decode(key, j, (char **)&blob, blob_size);
 303         free(key);
 304         if (ret < 0)
 305                 goto unmap;
 306         ret = key_type;
 307 unmap:
 308         ret2 = para_munmap(map, map_size);
 309         if (ret >= 0 && ret2 < 0)
 310                 ret = ret2;
 311         if (ret < 0) {
 312                 free(blob);
 313                 blob = NULL;
 314         }
 315 out:
 316         *result = blob;
 317         return ret;
 318 }
 319