Tomb/extras/kdf-keys/pbkdf2.c
2013-09-08 16:10:19 +02:00

145 lines
4.2 KiB
C

/*
** SYNOPSIS
** echo "passphrase" | pbkdf2 salt_hex count > 48_byte_hex_key_and_iv
**
** DESCRIPTION
**
** Make the "Password-Based Key Derivation Function v2" function found in
** the openssl library available to the command line, as it is not available
** for use from the "openssl" command. At the time of writing the "openssl"
** command only encrypts using the older, 'fast' pbkdf1.5 method.
**
** The 'salt_hex' is the salt to be used, as a hexadecimal string. Typically
** this is 8 bytes (64 bit), and is an assigned randomly during encryption.
**
** The 'count' is iteration count used to make the calculation of the key
** from the passphrase longer so as to take 1/2 to 2 seconds to generate.
** This complexity prevents slows down brute force attacks enormously.
**
** The output of the above is a 48 bytes in hexadeximal, which is typically
** used for 32 byte encryption key KEY and a 16 byte IV as needed by
** Crypt-AES-256 (or some other encryption method).
**
** NOTE: While the "openssl" command can accept a hex encoded 'key' and 'iv'
** it only does so on the command line, which is insecure. As such I
** recommend that the output only be used with API access to the "OpenSSL"
** cryptography libraries.
**
*************
**
** Anthony Thyssen 4 November 2009 A.Thyssen@griffith.edu.au
**
** Based on a test program "pkcs5.c" found on
** http://www.mail-archive.com/openssl-users@openssl.org
** which uses openssl to perform PBKDF2 (RFC2898) iteritive (slow) password
** hashing.
**
** Build
** gcc -o pbkdf2 pbkdf2.c -lcrypto
**
*/
#include <stdio.h>
#include <string.h>
#include <gcrypt.h>
/* TODO: move print_hex and hex_to_binary to utils.h, with separate compiling */
void print_hex(unsigned char *buf, int len)
{
int i;
for(i=0;i<len;i++)
printf("%02x", buf[i]);
printf("\n");
}
int hex_to_binary(unsigned char *buf, char *hex)
{
int ret;
int count=0;
while(*hex) {
if( hex[1] ) {
ret = sscanf( hex, "%2x", (unsigned int*) buf++ );
hex += 2;
}
else {
ret = sscanf( hex++, "%1x", (unsigned int*)buf++ );
}
count++;
if( ret != 1)
return -1;
}
*buf = 0; // null terminate -- precaution
return count;
}
int main(int argc, char *argv[])
{
char *pass = NULL;
unsigned char *salt;
int salt_len; // salt length in bytes
int ic=0; // iterative count
int result_len;
unsigned char *result; // result (binary - 32+16 chars)
int i;
if ( argc != 4 ) {
fprintf(stderr, "usage: %s salt count len <passwd >binary_key_iv\n", argv[0]);
exit(10);
}
//TODO: move to base64decode
salt=calloc(strlen(argv[1])/2+3, sizeof(char));
salt_len=hex_to_binary(salt, argv[1]);
if( salt_len <= 0 ) {
fprintf(stderr, "Error: %s is not a valid salt (it must be a hexadecimal string)\n", argv[1]);
exit(1);
}
if( sscanf(argv[2], "%d", &ic) == 0 || ic<=0) {
fprintf(stderr, "Error: count must be a positive integer\n");
exit(1);
}
if( sscanf(argv[3], "%d", &result_len) == 0 || result_len<=0) {
fprintf(stderr, "Error: result_len must be a positive integer\n");
exit(1);
}
fscanf(stdin, "%ms", &pass);
if ( pass[strlen(pass)-1] == '\n' )
pass[strlen(pass)-1] = '\0';
// PBKDF 2
result = calloc(result_len, sizeof(unsigned char*));
if (!gcry_check_version ("1.5.0")) {
fputs ("libgcrypt version mismatch\n", stderr);
exit (2);
}
/* Allocate a pool of 16k secure memory. This make the secure memory
available and also drops privileges where needed. */
gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
/* It is now okay to let Libgcrypt complain when there was/is
a problem with the secure memory. */
gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
/* Tell Libgcrypt that initialization has completed. */
gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
gcry_kdf_derive( pass, strlen(pass), GCRY_KDF_PBKDF2, GCRY_MD_SHA1, salt, salt_len, ic, result_len, result);
print_hex(result, result_len); // Key + IV (as hex string)
//clear and free everything
for(i=0; i<result_len;i++)
result[i]=0;
free(result);
for(i=0; i<strlen(pass); i++) //blank
pass[i]=0;
free(pass);
for(i=0; i<strlen(argv[1])/2+3; i++) //blank
salt[i]=0;
free(salt);
return(0);
}
/* vim: set noexpandtab ts=4 sw=4: */