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).