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libtomcrypt

NAME

libtomcrypt - public domain open source crypthographic toolkit

SYNOPSIS

#include <tomcrypt.h>

Link with -ltomcrypt (use pkg-config --libs libtomcrypt)

DESCRIPTION

libtomcrypt is documented in /usr/share/doc/libtomcrypt-dev/crypt.pdf. To give you a very brief introduction, the following example is provided.

EXAMPLE

   /* AES-XTS example for libtomcrypt. (c) 2008 Michael Stapelberg, Public Domain */
   #include <stdint.h>
   #include <string.h>
   #include <tomcrypt.h>
 
   static symmetric_xts xts;
 
   /*
    * Initializes AES-XTS for use with encrypt(). Key must be at least 32 bytes long, only
    * the first 32 bytes will be used.
    *
    */
   void initialize_xts(unsigned char *key) {
     int idx, err;
     unsigned char aeskey1[16], aeskey2[16];
 
     /* You can use 32 different ciphers simultaneously. Before using a cipher, you must register it. */
     register_cipher(&aes_desc);
 
     /* Get the index of the cipher registered before */
     if ((idx = find_cipher("aes")) == -1) {
             fprintf(stderr, "ERROR: AES not available in libtomcrypt. Please upgrade/fix libtomcrypt.\n");
             exit(EXIT_FAILURE);
     }
    
     /* Set up the two private keys required by AES-XTS (see 3.4.10 of crypt.pdf) */
     strncpy((char*)aeskey1, key, 16);
     strncpy((char*)aeskey2, key+16, 16);
     
     printf("Initializing with keys \"%.16s\" and \"%.16s\" (AES-XTS)\n", aeskey1, aeskey2);
    
     /* Initialize AES-XTS */
     if ((err = xts_start(idx, aeskey1, aeskey2, 16, 0, &xts)) != CRYPT_OK) {
             fprintf(stderr, "ERROR starting XTS: %s\n", error_to_string(err));
             exit(EXIT_FAILURE);
     }
   }
  
   /*
    * Encrypts the input (of input_size) and stores the result in output. The piece index
    * is required because XTS wants a tweak for each block so that it doesn't generate
    * patterns which would be visible in the encrypted output.
    *
    */
   void encrypt(const uint8_t *input, uint8_t *output, int input_size, int piece_idx) {
     unsigned char tweak[256];
     int err;
 
     memset(tweak, '\0', 256);
     snprintf((char*)tweak, 256, "%d", piece_idx);
     
     if ((err = xts_encrypt(input, input_size, output, tweak, &xts)) != CRYPT_OK) {
             fprintf(stderr, "ERROR in AES encryption: %d: %s\n", err, error_to_string(err));
             exit(EXIT_FAILURE);
     }
   }
 

SEE ALSO

pkg-config(1)

AUTHOR

libtomcrypt was written by Tom St Denis.

This manual page was written by Michael Stapelberg <michael@stapelberg.de>, for the Debian project (and may be used by others).