crypt_common.c

   1 /*
   2  * Copyright (C) 2005 Andre Noll <maan@tuebingen.mpg.de>
   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  * Read a 4-byte number from a buffer in big-endian format.
  50  *
  51  * \param vp The buffer.
  52  *
  53  * The byte-order of the buffer is expected to be big-endian, unlike read_u32()
  54  * of portable_io.h which expects little endian.
  55  *
  56  * \return The 32 bit number given by \a vp.
  57  */
  58 uint32_t read_ssh_u32(const void *vp)
  59 {
  60         const unsigned char *p = (const unsigned char *)vp;
  61         uint32_t v;
  62
  63         v  = (uint32_t)p[0] << 24;
  64         v |= (uint32_t)p[1] << 16;
  65         v |= (uint32_t)p[2] << 8;
  66         v |= (uint32_t)p[3];
  67
  68         return v;
  69 }
  70
  71 /**
  72  * Sanity checks for the header of an ssh key.
  73  *
  74  * \param blob The buffer.
  75  * \param blen The number of bytes of \a blob.
  76  *
  77  * This performs some checks to make sure we really have an ssh key. It also
  78  * computes the offset in bytes of the start of the key values (modulus,
  79  * exponent..).
  80  *
  81  * \return The number of bytes to skip until the start of the first encoded
  82  * number (usually 11).
  83  */
  84 int check_ssh_key_header(const unsigned char *blob, int blen)
  85 {
  86         const unsigned char *p = blob, *end = blob + blen;
  87         uint32_t rlen;
  88
  89         if (p + 4 > end)
  90                 return -E_SSH_KEY_HEADER;
  91         rlen = read_ssh_u32(p);
  92         p += 4;
  93         if (p + rlen < p)
  94                 return -E_SSH_KEY_HEADER;
  95         if (p + rlen > end)
  96                 return -E_SSH_KEY_HEADER;
  97         if (rlen < strlen(KEY_TYPE_TXT))
  98                 return -E_SSH_KEY_HEADER;
  99         PARA_DEBUG_LOG("type: %s, rlen: %u\n", p, rlen);
 100         if (strncmp((char *)p, KEY_TYPE_TXT, strlen(KEY_TYPE_TXT)))
 101                 return -E_SSH_KEY_HEADER;
 102         return 4 + rlen;
 103 }
 104
 105 /**
 106  * Check existence and permissions of a private key file.
 107  *
 108  * \param file The path of the key file.
 109  *
 110  * This checks whether the file exists and its permissions are restrictive
 111  * enough. It is considered an error if we own the file and it is readable for
 112  * others.
 113  *
 114  * \return Standard.
 115  */
 116 int check_private_key_file(const char *file)
 117 {
 118         struct stat st;
 119
 120         if (stat(file, &st) != 0)
 121                 return -ERRNO_TO_PARA_ERROR(errno);
 122         if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0)
 123                 return -E_KEY_PERM;
 124         return 1;
 125 }
 126
 127 void hash_to_asc(unsigned char *hash, char *asc)
 128 {
 129         int i;
 130         const char hexchar[] = "0123456789abcdef";
 131
 132         for (i = 0; i < HASH_SIZE; i++) {
 133                 asc[2 * i] = hexchar[hash[i] >> 4];
 134                 asc[2 * i + 1] = hexchar[hash[i] & 0xf];
 135         }
 136         asc[2 * HASH_SIZE] = '\0';
 137 }
 138
 139 int hash_compare(unsigned char *h1, unsigned char *h2)
 140 {
 141         int i;
 142
 143         for (i = 0; i < HASH_SIZE; i++) {
 144                 if (h1[i] < h2[i])
 145                         return -1;
 146                 if (h1[i] > h2[i])
 147                         return 1;
 148         }
 149         return 0;
 150 }