2 * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
20 FILE_LICENCE ( GPL2_OR_LATER );
24 * Hash-based derivation function (Hash_df)
26 * This algorithm is designed to comply with ANS X9.82 Part 3-2007
27 * Section 10.5.2. This standard is not freely available, but most of
28 * the text appears to be shared with NIST SP 800-90, which can be
31 * http://csrc.nist.gov/publications/nistpubs/800-90/SP800-90revised_March2007.pdf
33 * Where possible, references are given to both documents. In the
34 * case of any disagreement, ANS X9.82 takes priority over NIST SP
35 * 800-90. (In particular, note that some algorithms that are
36 * Approved by NIST SP 800-90 are not Approved by ANS X9.82.)
43 #include <ipxe/crypto.h>
44 #include <ipxe/hash_df.h>
47 * Distribute entropy throughout a buffer
49 * @v hash Underlying hash algorithm
51 * @v input_len Length of input data, in bytes
52 * @v output Output buffer
53 * @v output_len Length of output buffer, in bytes
55 * This is the Hash_df function defined in ANS X9.82 Part 3-2007
56 * Section 10.5.2 (NIST SP 800-90 Section 10.4.1).
58 * The number of bits requested is implicit in the length of the
59 * output buffer. Requests must be for an integral number of bytes.
61 * The output buffer is filled incrementally with each iteration of
62 * the central loop, rather than constructing an overall "temp" and
63 * then taking the leftmost(no_of_bits_to_return) bits.
65 * There is no way for the Hash_df function to fail. The returned
66 * status SUCCESS is implicit.
68 void hash_df ( struct digest_algorithm *hash, const void *input,
69 size_t input_len, void *output, size_t output_len ) {
70 uint8_t context[hash->ctxsize];
71 uint8_t digest[hash->digestsize];
76 uint32_t no_of_bits_to_return;
77 } __attribute__ (( packed )) prefix;
81 DBGC ( &hash_df, "HASH_DF input:\n" );
82 DBGC_HDA ( &hash_df, 0, input, input_len );
85 assert ( input != NULL );
86 assert ( output != NULL );
88 /* 1. temp = the Null string
89 * 2. len = ceil ( no_of_bits_to_return / outlen )
91 * (Nothing to do. We fill the output buffer incrementally,
92 * rather than constructing the complete "temp" in-memory.
93 * "len" is implicit in the number of iterations required to
94 * fill the output buffer, and so is not calculated
98 /* 3. counter = an 8-bit binary value representing the integer "1" */
101 /* 4. For i = 1 to len do */
102 for ( temp = output, remaining = output_len ; remaining > 0 ; ) {
104 /* Comment: in step 5.1 (sic), no_of_bits_to_return is
105 * used as a 32-bit string.
107 * 4.1 temp = temp || Hash ( counter || no_of_bits_to_return
110 prefix.no_of_bits_to_return = htonl ( output_len * 8 );
111 digest_init ( hash, context );
112 digest_update ( hash, context, &prefix.counter,
113 ( sizeof ( prefix ) -
114 offsetof ( typeof ( prefix ), counter ) ) );
115 digest_update ( hash, context, input, input_len );
116 digest_final ( hash, context, digest );
118 /* 4.2 counter = counter + 1 */
121 /* 5. requested_bits = Leftmost ( no_of_bits_to_return )
124 * (We fill the output buffer incrementally.)
126 frag_len = sizeof ( digest );
127 if ( frag_len > remaining )
128 frag_len = remaining;
129 memcpy ( temp, digest, frag_len );
131 remaining -= frag_len;
134 /* 6. Return SUCCESS and requested_bits */
135 DBGC ( &hash_df, "HASH_DF output:\n" );
136 DBGC_HDA ( &hash_df, 0, output, output_len );