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.\" Hey, EMACS: -*- nroff -*-
.\" First parameter, NAME, should be all caps
.\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
.\" other parameters are allowed: see man(7), man(1)
.TH LIBTOMCRYPT 3 "June 2009"
.\" Please adjust this date whenever revising the manpage.
.\"
.\" Some roff macros, for reference:
.\" .nh disable hyphenation
.\" .hy enable hyphenation
.\" .ad l left justify
.\" .ad b justify to both left and right margins
.\" .nf disable filling
.\" .fi enable filling
.\" .br insert line break
.\" .sp <n> insert n+1 empty lines
.\" for manpage-specific macros, see man(7)
.SH NAME
libtomcrypt \- public domain open source crypthographic toolkit
.SH SYNOPSIS
#include <tomcrypt.h>
Link with \-ltomcrypt (use pkg-config \-\-libs libtomcrypt)
.SH DESCRIPTION
.B libtomcrypt
is documented in /usr/share/doc/libtomcrypt-dev/crypt.pdf. To give you a very
brief introduction, the following example is provided.
.SH EXAMPLE
.nf
/* 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);
}
}
.fi
.SH SEE ALSO
.BR pkg-config (1)
.SH AUTHOR
libtomcrypt was written by Tom St Denis.
.PP
This manual page was written by Michael Stapelberg <michael@stapelberg.de>,
for the Debian project (and may be used by others).
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