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).
June 2009