1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
|
/*
* 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., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** @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;
}
|
