rmt/cipher.c

   1 #include <sys/types.h>
   2 #include <fcntl.h>
   3 #include <unistd.h>
   4 #include <stdlib.h>
   5 #include <stdio.h>
   6 #include <syslog.h>
   7 #include <strings.h>
   8 #include <errno.h>
   9 #include <openssl/evp.h>
  10
  11 /*
  12  * Encrypt or decrypt buf, returning a pointer to the transformed data,
  13  * or NULL on error.
  14  * The returned data is the same size as the input data,
  15  * which means we must turn off cipher padding, and require that buflen
  16  * be a multiple of the cipher block size (8 for Blowfish).
  17  * To keep things simple, the return value is a malloc'd
  18  * buffer that is overwritten on each call.
  19  *
  20  * Ken Lalonde <ken@globalremit.com>, 2003
  21  */
  22 char *
  23 cipher(char *buf, int buflen, int do_encrypt)
  24 {
  25         static EVP_CIPHER_CTX ctx;
  26         static char *out = NULL;        /* return value, grown as necessary */
  27         static int outlen = 0;
  28         static int init = 0, which, blocksize;
  29         int n;
  30
  31         if (!init) {
  32                 static const EVP_CIPHER *cipher;
  33                 unsigned char key[EVP_MAX_KEY_LENGTH], iv[EVP_MAX_IV_LENGTH];
  34                 // Read key from $HOME/.ermt.key
  35                 char *keyfile = ".ermt.key";
  36                 unsigned char buf[128];
  37                 FILE *fp;
  38                 int i;
  39
  40                 openlog("ermt", LOG_PID, LOG_DAEMON);
  41                 // Not needed: OpenSSL_add_all_algorithms();
  42                 // Not needed: ERR_load_crypto_strings();
  43                 cipher = EVP_bf_cbc();  // or: EVP_aes_{128,192,256}_cbc()
  44                 // We want the ability to decrypt the output
  45                 // using "openssl enc -d -kfile K -nopad -nosalt", which
  46                 // means we must read the key file the same way
  47                 // openssl does.  But be careful: if the key contains
  48                 // \0 or \r or \n, the effective size will be reduced.
  49                 if ((fp = fopen(keyfile, "r")) == NULL) {
  50                         syslog(LOG_ERR, "Can't open key file %s: %m", keyfile);
  51                         return NULL;
  52                 }
  53                 buf[0] = '\0';
  54                 fgets(buf, sizeof buf, fp);
  55                 fclose(fp);
  56                 i = strlen(buf);
  57                 if ((i > 0) &&
  58                         ((buf[i-1] == '\n') || (buf[i-1] == '\r')))
  59                         buf[--i]='\0';
  60                 if ((i > 0) &&
  61                         ((buf[i-1] == '\n') || (buf[i-1] == '\r')))
  62                         buf[--i]='\0';
  63                 if (i < 1) {
  64                         syslog(LOG_ERR, "zero length key");
  65                         errno = EINVAL;
  66                         return NULL;
  67                 }
  68                 EVP_BytesToKey(cipher, EVP_md5(), NULL,
  69                         buf, strlen(buf), 1, key, iv);
  70                 EVP_CIPHER_CTX_init(&ctx);
  71                 EVP_CipherInit_ex(&ctx, cipher, NULL, key, iv, do_encrypt);
  72                 EVP_CIPHER_CTX_set_padding(&ctx, 0);    // -nopad
  73                 OPENSSL_cleanse(buf, sizeof buf);
  74                 OPENSSL_cleanse(key, sizeof key);
  75                 OPENSSL_cleanse(iv, sizeof iv);
  76                 blocksize = EVP_CIPHER_CTX_block_size(&ctx);
  77                 which = do_encrypt;
  78                 init = 1;
  79         }
  80         if (which != do_encrypt) {
  81                 syslog(LOG_ERR, "Cannot switch modes");
  82                 errno = EINVAL;
  83                 return NULL;
  84         }
  85         if ((buflen % blocksize) != 0) {
  86                 syslog(LOG_ERR, "Buffer size is not a multiple of cipher block size");
  87                 errno = EINVAL;
  88                 return NULL;
  89         }
  90         if (outlen < buflen+blocksize) {
  91                 outlen = (buflen+blocksize) * 2;
  92                 out = realloc(out, outlen);
  93         }
  94         if (!EVP_CipherUpdate(&ctx, out, &n, buf, buflen)) {
  95                 syslog(LOG_ERR, "EVP_CipherUpdate failed");
  96                 errno = EINVAL;
  97                 return NULL;
  98         }
  99         if (n != buflen) {
 100                 syslog(LOG_ERR, "EVP_CipherUpdate: %d != %d", n, buflen);
 101                 errno = EINVAL;
 102                 return NULL;
 103         }
 104         // assert(ctx->buf_len == 0);
 105         return out;
 106 }
 107
 108 /* Decrypt stdin to stdout, and exit */
 109 int
 110 decrypt()
 111 {
 112         char buf[8*1024], *cp;
 113         int n;
 114
 115         while ((n = fread(buf, 1, sizeof buf, stdin)) > 0) {
 116                 if ((cp = cipher(buf, n, 0)) == NULL) {
 117                         fprintf(stderr, "ermt: Error decoding input; see daemon.err syslog\n");
 118                         exit(1);
 119                 }
 120                 fwrite(cp, 1, n, stdout);
 121         }
 122         if (ferror(stdin)) {
 123                 perror("ermt: stdin: read");
 124                 exit(1);
 125         }
 126         if (fflush(stdout)) {
 127                 perror("ermt: stdout: write");
 128                 exit(1);
 129         }
 130         exit(0);
 131 }