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1 | /* -*-c-*- |
2 | * | |
3 | * Common definitions for OCB and related modes | |
4 | * | |
5 | * (c) 2018 Straylight/Edgeware | |
6 | */ | |
7 | ||
8 | /*----- Licensing notice --------------------------------------------------* | |
9 | * | |
10 | * This file is part of Catacomb. | |
11 | * | |
12 | * Catacomb is free software: you can redistribute it and/or modify it | |
13 | * under the terms of the GNU Library General Public License as published | |
14 | * by the Free Software Foundation; either version 2 of the License, or | |
15 | * (at your option) any later version. | |
16 | * | |
17 | * Catacomb is distributed in the hope that it will be useful, but | |
18 | * WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | * Library General Public License for more details. | |
21 | * | |
22 | * You should have received a copy of the GNU Library General Public | |
23 | * License along with Catacomb. If not, write to the Free Software | |
24 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, | |
25 | * USA. | |
26 | */ | |
27 | ||
28 | #ifndef CATACOMB_OCB_H | |
29 | #define CATACOMB_OCB_H | |
30 | ||
31 | #ifdef __cplusplus | |
32 | extern "C" { | |
33 | #endif | |
34 | ||
35 | /*----- Header files ------------------------------------------------------*/ | |
36 | ||
37 | #include <stddef.h> | |
38 | ||
39 | #include <mLib/bits.h> | |
40 | #include <mLib/compiler.h> | |
41 | ||
42 | /*----- Constants ---------------------------------------------------------*/ | |
43 | ||
44 | /* The number of offsets to maintain. Rather than calculate and store all | |
45 | * possible offset values in advance, or calculate new ones on demand (and | |
46 | * have to allocate space for them), we calculate a number in advance, and | |
47 | * determine any others every time they're needed. If we calculate the first | |
48 | * %$n$% offsets only, then we spend %$i - n + 1$% time calculating offset | |
49 | * %$L_i$% when %$i \ge n$%. But the offset %$L_i$% is used only for a | |
50 | * %$2^{-i-1}$% fraction of the blocks. Summing up this geometric series | |
51 | * shows us that we add only a small constant overhead, and save storage | |
52 | * space for many offsets. | |
53 | */ | |
54 | #define OCB_NCALC 16 | |
55 | #define OCB_CALCMASK ((1ul << OCB_NCALC) - 1) | |
56 | ||
57 | /*----- Functions provided ------------------------------------------------*/ | |
58 | ||
59 | /* --- @ocb_ctz@, @ocb_ctzl@ --- * | |
60 | * | |
61 | * Arguments: @unsigned i@ or @unsigned long i@ = operand, assumed nonzero | |
62 | * | |
63 | * Returns: The number of trailing zero bits in @i@, or nonsense if | |
64 | * %$i = 0$%. | |
65 | */ | |
66 | ||
67 | extern unsigned ocb_ctz(unsigned /*i*/); | |
68 | extern unsigned ocb_ctzl(unsigned long /*i*/); | |
69 | ||
70 | #if GCC_VERSION_P(3, 4) | |
71 | # define OCB_CTZ(i) __builtin_ctz(i) | |
72 | # define OCB_CTZL(i) __builtin_ctzl(i) | |
73 | #else | |
74 | # define OCB_CTZ(i) ocb_ctz(i) | |
75 | # define OCB_CTZL(i) ocb_ctzl(i) | |
76 | #endif | |
77 | ||
78 | /* --- @OCB_OFFSET@ --- * | |
79 | * | |
80 | * Arguments: @PRE@ = block cipher prefix | |
81 | * @uint32 *o@ = pointer to offset accumulator | |
82 | * @uint32 (*l)[PRE_BLKSZ]@ = pointer to offset mask table | |
83 | * @unsigned long i@ = block index | |
84 | * | |
85 | * Returns: --- | |
86 | * | |
87 | * Use: Update the per-block offset for Grey-code-based OCB | |
88 | * variants. On entry, @o@ is assumed to hold the offset for | |
89 | * block @i - 1@; on exit @o@ is updated to hold the offset for | |
90 | * block @i@. | |
91 | */ | |
92 | ||
93 | #define OCB_OFFSET(PRE, o, l, i) do { \ | |
94 | uint32 (*_l)[PRE##_BLKSZ/4] = (l); \ | |
95 | uint32 *_o = (o); \ | |
96 | unsigned long _i = (i); \ | |
97 | unsigned _j; \ | |
98 | \ | |
99 | if (_i&OCB_CALCMASK) { \ | |
100 | _j = OCB_CTZ(_i); \ | |
101 | BLKC_XMOVE(PRE, _o, _l[_j]); \ | |
102 | } else { \ | |
103 | uint32 _t[PRE##_BLKSZ]; \ | |
104 | _j = OCB_CTZL(_i) - OCB_NCALC; \ | |
105 | BLKC_BLSHIFT(PRE, IRRED, _t, _l[OCB_NCALC - 1]); \ | |
106 | while (_j--) BLKC_BLSHIFT(PRE, IRRED, _t, _t); \ | |
107 | BLKC_XMOVE(PRE, _t, _l[_j]); \ | |
108 | } \ | |
109 | } while (0) | |
110 | ||
111 | /*----- That's all, folks -------------------------------------------------*/ | |
112 | ||
113 | #ifdef __cplusplus | |
114 | } | |
115 | #endif | |
116 | ||
117 | #endif |