crypt.c

   1 /*
   2  * Copyright (C) 2005-2009 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file crypt.c openssl-based RSA encryption/decryption routines */
   8
   9 #include "para.h"
  10 #include "error.h"
  11 #include "string.h"
  12 #include "crypt.h"
  13 #include <openssl/rand.h>
  14 #include <openssl/err.h>
  15
  16 /**
  17  * Fill a buffer with random content.
  18  *
  19  * \param buf The buffer to fill.
  20  * \param num The size of \a buf in bytes.
  21  *
  22  * This function puts \a num cryptographically strong pseudo-random bytes into
  23  * buf. If libssl can not guarantee an unpredictable byte sequence (for example
  24  * because the PRNG has not been seeded with enough randomness) the function
  25  * logs an error message and calls exit().
  26  */
  27 void get_random_bytes_or_die(unsigned char *buf, int num)
  28 {
  29         unsigned long err;
  30
  31         /* RAND_bytes() returns 1 on success, 0 otherwise. */
  32         if (RAND_bytes(buf, num) == 1)
  33                 return;
  34         err = ERR_get_error();
  35         PARA_EMERG_LOG("%s\n", ERR_reason_error_string(err));
  36         exit(EXIT_FAILURE);
  37 }
  38
  39 /**
  40  * Seed pseudo random number generators.
  41  *
  42  * This function reads 64 bytes from /dev/urandom and adds them to the SSL
  43  * PRNG. It also seeds the PRNG used by random() with a random seed obtained
  44  * from SSL. If /dev/random could not be read, an error message is logged and
  45  * the function calls exit().
  46  *
  47  * \sa RAND_load_file(3), \ref get_random_bytes_or_die(), srandom(3),
  48  * random(3), \ref para_random().
  49  */
  50 void init_random_seed_or_die(void)
  51 {
  52         int seed, ret = RAND_load_file("/dev/urandom", 64);
  53
  54         if (ret != 64) {
  55                 PARA_EMERG_LOG("could not seed PRNG (ret = %d)\n", ret);
  56                 exit(EXIT_FAILURE);
  57         }
  58         get_random_bytes_or_die((unsigned char *)&seed, sizeof(seed));
  59         srandom(seed);
  60 }
  61
  62 static EVP_PKEY *load_key(const char *file, int private)
  63 {
  64         BIO *key;
  65         EVP_PKEY *pkey = NULL;
  66
  67         key = BIO_new(BIO_s_file());
  68         if (!key)
  69                 return NULL;
  70         if (BIO_read_filename(key, file) > 0) {
  71                 if (private == LOAD_PRIVATE_KEY)
  72                         pkey = PEM_read_bio_PrivateKey(key, NULL, NULL, NULL);
  73                 else
  74                         pkey = PEM_read_bio_PUBKEY(key, NULL, NULL, NULL);
  75         }
  76         BIO_free(key);
  77         return pkey;
  78 }
  79
  80 /**
  81  * read an RSA key from a file
  82  *
  83  * \param key_file the file containing the key
  84  * \param rsa RSA structure is returned here
  85  * \param private if non-zero, read the private key, otherwise the public key
  86  *
  87  * \return The size of the RSA key on success, negative on errors.
  88  *
  89  * \sa openssl(1), rsa(1).
  90  */
  91 int get_rsa_key(char *key_file, RSA **rsa, int private)
  92 {
  93         EVP_PKEY *key = load_key(key_file, private);
  94
  95         if (!key)
  96                 return (private == LOAD_PRIVATE_KEY)? -E_PRIVATE_KEY
  97                         : -E_PUBLIC_KEY;
  98         *rsa = EVP_PKEY_get1_RSA(key);
  99         EVP_PKEY_free(key);
 100         if (!*rsa)
 101                 return -E_RSA;
 102         return RSA_size(*rsa);
 103 }
 104
 105 /**
 106  * free an RSA structure
 107  *
 108  * \param rsa pointer to the RSA struct to free
 109  *
 110  * This must be called for any key obtained by get_rsa_key().
 111  */
 112 void rsa_free(RSA *rsa)
 113 {
 114         if (rsa)
 115                 RSA_free(rsa);
 116 }
 117
 118 /**
 119  * decrypt a buffer using an RSA key
 120  *
 121  * \param key_file full path of the rsa key
 122  * \param outbuf the output buffer
 123  * \param inbuf the encrypted input buffer
 124  * \param rsa_inlen the length of \a inbuf
 125  *
 126  * The \a outbuf must be large enough to hold at least \a rsa_inlen bytes.
 127  *
 128  * \return The size of the recovered plaintext on success, negative on errors.
 129  *
 130  * \sa RSA_private_decrypt(3)
 131  **/
 132 int para_decrypt_buffer(char *key_file, unsigned char *outbuf, unsigned char *inbuf,
 133                         unsigned rsa_inlen)
 134 {
 135         RSA *rsa;
 136         int ret, inlen = rsa_inlen;
 137
 138         if (inlen < 0)
 139                 return -E_RSA;
 140         ret = get_rsa_key(key_file, &rsa, LOAD_PRIVATE_KEY);
 141         if (ret < 0)
 142                 return ret;
 143         ret = RSA_private_decrypt(inlen, inbuf, outbuf, rsa, RSA_PKCS1_PADDING);
 144         rsa_free(rsa);
 145         return (ret > 0)? ret : -E_DECRYPT;
 146 }
 147
 148 /**
 149  * decrypt the challenge number sent by para_server
 150  *
 151  * \param key_file full path of the rsa key
 152  * \param challenge_nr result is stored here
 153  * \param inbuf the input buffer
 154  * \param rsa_inlen the length of \a inbuf
 155  *
 156  * \return positive on success, negative on errors
 157  *
 158  * \sa para_decrypt_buffer()
 159  */
 160 int para_decrypt_challenge(char *key_file, long unsigned *challenge_nr,
 161                 unsigned char *inbuf, unsigned rsa_inlen)
 162 {
 163         unsigned char *rsa_out = OPENSSL_malloc(rsa_inlen + 1);
 164         int ret = para_decrypt_buffer(key_file, rsa_out, inbuf, rsa_inlen);
 165
 166         if (ret >= 0) {
 167                 rsa_out[ret] = '\0';
 168                 ret = sscanf((char *)rsa_out, "%lu", challenge_nr) == 1?
 169                         1 : -E_CHALLENGE;
 170         }
 171         OPENSSL_free(rsa_out);
 172         return ret;
 173 }
 174
 175 /**
 176  * encrypt a buffer using an RSA key
 177  *
 178  * \param rsa: public rsa key
 179  * \param inbuf the input buffer
 180  * \param len the length of \a inbuf
 181  * \param outbuf the output buffer
 182  *
 183  * \return The size of the encrypted data on success, negative on errors
 184  *
 185  * \sa RSA_public_encrypt(3)
 186  */
 187 int para_encrypt_buffer(RSA *rsa, unsigned char *inbuf,
 188                 unsigned len, unsigned char *outbuf)
 189 {
 190         int ret, flen = len; /* RSA_public_encrypt expects a signed int */
 191
 192         if (flen < 0)
 193                 return -E_ENCRYPT;
 194         ret = RSA_public_encrypt(flen, inbuf, outbuf, rsa, RSA_PKCS1_PADDING);
 195         return ret < 0?  -E_ENCRYPT : ret;
 196 }
 197
 198 /**
 199  * encrypt the given challenge number
 200  *
 201  * \param rsa: public rsa key
 202  * \param challenge_nr the number to be encrypted
 203  * \param outbuf the output buffer
 204  *
 205  * \a outbuf must be at least 64 bytes long
 206  *
 207  * \return The size of the encrypted data on success, negative on errors
 208  *
 209  * \sa para_encrypt_buffer()
 210  *
 211  */
 212 int para_encrypt_challenge(RSA* rsa, long unsigned challenge_nr,
 213         unsigned char *outbuf)
 214 {
 215         unsigned char *inbuf = (unsigned char*) make_message("%lu", challenge_nr);
 216         int ret = para_encrypt_buffer(rsa, inbuf, strlen((char *)inbuf), outbuf);
 217         free(inbuf);
 218         return ret;
 219 }
 220