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_ssh_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(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(unsigned char *h1, 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 }