/*
* Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
/** @file
*
* Hash-based derivation function (Hash_df)
*
* This algorithm is designed to comply with ANS X9.82 Part 3-2007
* Section 10.5.2. This standard is not freely available, but most of
* the text appears to be shared with NIST SP 800-90, which can be
* downloaded from
*
* http://csrc.nist.gov/publications/nistpubs/800-90/SP800-90revised_March2007.pdf
*
* Where possible, references are given to both documents. In the
* case of any disagreement, ANS X9.82 takes priority over NIST SP
* 800-90. (In particular, note that some algorithms that are
* Approved by NIST SP 800-90 are not Approved by ANS X9.82.)
*/
#include <stdint.h>
#include <string.h>
#include <assert.h>
#include <byteswap.h>
#include <ipxe/crypto.h>
#include <ipxe/hash_df.h>
/**
* Distribute entropy throughout a buffer
*
* @v hash Underlying hash algorithm
* @v input Input data
* @v input_len Length of input data, in bytes
* @v output Output buffer
* @v output_len Length of output buffer, in bytes
*
* This is the Hash_df function defined in ANS X9.82 Part 3-2007
* Section 10.5.2 (NIST SP 800-90 Section 10.4.1).
*
* The number of bits requested is implicit in the length of the
* output buffer. Requests must be for an integral number of bytes.
*
* The output buffer is filled incrementally with each iteration of
* the central loop, rather than constructing an overall "temp" and
* then taking the leftmost(no_of_bits_to_return) bits.
*
* There is no way for the Hash_df function to fail. The returned
* status SUCCESS is implicit.
*/
void hash_df ( struct digest_algorithm *hash, const void *input,
size_t input_len, void *output, size_t output_len ) {
uint8_t context[hash->ctxsize];
uint8_t digest[hash->digestsize];
size_t frag_len;
struct {
uint8_t pad[3];
uint8_t counter;
uint32_t no_of_bits_to_return;
} __attribute__ (( packed )) prefix;
void *temp;
size_t remaining;
DBGC ( &hash_df, "HASH_DF input:\n" );
DBGC_HDA ( &hash_df, 0, input, input_len );
/* Sanity checks */
assert ( input != NULL );
assert ( output != NULL );
/* 1. temp = the Null string
* 2. len = ceil ( no_of_bits_to_return / outlen )
*
* (Nothing to do. We fill the output buffer incrementally,
* rather than constructing the complete "temp" in-memory.
* "len" is implicit in the number of iterations required to
* fill the output buffer, and so is not calculated
* explicitly.)
*/
/* 3. counter = an 8-bit binary value representing the integer "1" */
prefix.counter = 1;
/* 4. For i = 1 to len do */
for ( temp = output, remaining = output_len ; remaining > 0 ; ) {
/* Comment: in step 5.1 (sic), no_of_bits_to_return is
* used as a 32-bit string.
*
* 4.1 temp = temp || Hash ( counter || no_of_bits_to_return
* || input_string )
*/
prefix.no_of_bits_to_return = htonl ( output_len * 8 );
digest_init ( hash, context );
digest_update ( hash, context, &prefix.counter,
( sizeof ( prefix ) -
offsetof ( typeof ( prefix ), counter ) ) );
digest_update ( hash, context, input, input_len );
digest_final ( hash, context, digest );
/* 4.2 counter = counter + 1 */
prefix.counter++;
/* 5. requested_bits = Leftmost ( no_of_bits_to_return )
* of temp
*
* (We fill the output buffer incrementally.)
*/
frag_len = sizeof ( digest );
if ( frag_len > remaining )
frag_len = remaining;
memcpy ( temp, digest, frag_len );
temp += frag_len;
remaining -= frag_len;
}
/* 6. Return SUCCESS and requested_bits */
DBGC ( &hash_df, "HASH_DF output:\n" );
DBGC_HDA ( &hash_df, 0, output, output_len );
return;
}
