| 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 |