| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Key size management |
| 4 | * |
| 5 | * (c) 2007 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 |
| 13 | * it under the terms of the GNU Library General Public License as |
| 14 | * published by the Free Software Foundation; either version 2 of the |
| 15 | * License, or (at your option) any later version. |
| 16 | * |
| 17 | * Catacomb is distributed in the hope that it will be useful, |
| 18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | * GNU 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 |
| 24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 25 | * MA 02111-1307, USA. |
| 26 | */ |
| 27 | |
| 28 | #ifndef CATACOMB_KEYSZ_H |
| 29 | #define CATACOMB_KEYSZ_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 | |
| 41 | /*----- Data structures ---------------------------------------------------*/ |
| 42 | |
| 43 | /* --- Key size type constants --- * |
| 44 | * |
| 45 | * A key size limitation is an array of bytes. The first byte describes the |
| 46 | * kind of limitation on the key size %$k$%; the rest are argument bytes |
| 47 | * %$a_i$%, for %$i \ge 0$%. In all cases, %$a_0$% is the `recommended' key |
| 48 | * size. |
| 49 | * |
| 50 | * * @KSZ_ANY@ means there is no restriction. |
| 51 | * |
| 52 | * * @KSZ_RANGE@ requires that %$k \ge a_1$%, %$k \equiv 0 \pmod{a_3}$%, |
| 53 | * and, if %$a_2 \ne 0$%, %$k \le a_2$%. |
| 54 | * |
| 55 | * * @KSZ_SET@ requires that %$k \in {\,a_i\,}$%. |
| 56 | */ |
| 57 | |
| 58 | #define KSZ_OPMASK 0x1f /* Kinds of keysize specs */ |
| 59 | enum { |
| 60 | KSZ_ANY, /* Allows any key at all */ |
| 61 | KSZ_RANGE, /* Allows keys within a range */ |
| 62 | KSZ_SET /* Allows specific sizes of keys */ |
| 63 | }; |
| 64 | |
| 65 | #define KSZ_16BIT 0x20 /* Arguments are 16 bits long */ |
| 66 | |
| 67 | /*----- Key sizes for symmetric algorithms --------------------------------*/ |
| 68 | |
| 69 | /* --- @keysz@ --- * |
| 70 | * |
| 71 | * Arguments: @size_t sz@ = a proposed key size, or zero |
| 72 | * @const octet *ksz@ = pointer to key size table |
| 73 | * |
| 74 | * Returns: See below. |
| 75 | * |
| 76 | * Use: Returns a sensible key size. If @sz@ is nonzero, it is |
| 77 | * interpreted as an amount (in bytes) of key material which the |
| 78 | * caller has available, and the return value is either the |
| 79 | * largest allowable key size less than or equal to the caller's |
| 80 | * size, or zero if there is no valid key length small enough. |
| 81 | * If @sz@ is zero, the function returns a `recommended' key |
| 82 | * size. |
| 83 | */ |
| 84 | |
| 85 | extern size_t keysz(size_t /*sz*/, const octet */*ksz*/); |
| 86 | |
| 87 | #define KSZ_CHECK(pre, sz) (keysz((sz), pre##_keysz) == (sz)) |
| 88 | #define KSZ_ASSERT(pre, sz) \ |
| 89 | assert(((void)"Bad key size for " #pre, KSZ_CHECK(pre, sz))) |
| 90 | |
| 91 | /* --- @keysz_pad@ --- * |
| 92 | * |
| 93 | * Arguments: @size_t sz@ = a proposed key size |
| 94 | * @const octet *ksz@ = pointer to key size table |
| 95 | * |
| 96 | * Returns: A key size, at least as large as @sz@, or zero if no such |
| 97 | * size is available. |
| 98 | */ |
| 99 | |
| 100 | extern size_t keysz_pad(size_t /*sz*/, const octet */*ksz*/); |
| 101 | |
| 102 | /*----- Key size conversions ----------------------------------------------*/ |
| 103 | |
| 104 | /* --- @keysz_fromdl@, @_fromschnorr@, @_fromif@, @_fromec@ --- * |
| 105 | * |
| 106 | * Arguments: @double nbits@ = key size |
| 107 | * |
| 108 | * Returns: Equivalent symmetric key size. |
| 109 | * |
| 110 | * Use: Converts key lengths of various kinds of reference problems |
| 111 | * to (roughly) equivalent symmetric key sizes. |
| 112 | * |
| 113 | * * Given the bit length of %$p$%, @keysz_fromdl@ returns a |
| 114 | * key size representing the difficulty of computing |
| 115 | * discrete logarithms in %$\gf{p}$%, for %$p$% prime or a |
| 116 | * small power of a prime. |
| 117 | * |
| 118 | * * Given the bit length of %$r$%, @keysz_fromschnorr@ |
| 119 | * returns a key size representing the difficulty of |
| 120 | * computing discrete logarithms in a subgroup of %$\gf{q}$% |
| 121 | * of order %$r$%. |
| 122 | * |
| 123 | * * Given the bit length of %$n$%, @keysz_fromif@ returns a |
| 124 | * key size representing the difficulty of factoring a |
| 125 | * `hard' number %$n = p q$%, where %$p$% and %$q$% are |
| 126 | * primes of (near enough) the same length. |
| 127 | * |
| 128 | * * Given the bit length of %$r$%, @keysz_fromec@ returns a |
| 129 | * key size representing the difficulty of computing |
| 130 | * discrete logarithms in a subgroup of order-%$r$% of an |
| 131 | * elliptic curve over a finite field. |
| 132 | * |
| 133 | * These functions take and return @double@ rather than an |
| 134 | * integer type in order to preserve precision between |
| 135 | * conversions. |
| 136 | */ |
| 137 | |
| 138 | extern double keysz_fromdl(double /*nbits*/); |
| 139 | extern double keysz_fromschnorr(double /*nbits*/); |
| 140 | extern double keysz_fromif(double /*nbits*/); |
| 141 | extern double keysz_fromec(double /*nbits*/); |
| 142 | |
| 143 | /* --- @keysz_todl@, @_toschnorr@, @_toif@, @_toec@ --- * |
| 144 | * |
| 145 | * Arguments: @unsigned long nbits@ = symmetric key size |
| 146 | * |
| 147 | * Returns: Equivalent key size. |
| 148 | * |
| 149 | * Use: Converts symmetric key sizes to (roughly) equivalent key |
| 150 | * sizes for various kinds of reference problems. These are the |
| 151 | * approximate inverses of the functions above. |
| 152 | */ |
| 153 | |
| 154 | extern double keysz_todl(double /*nbits*/); |
| 155 | extern double keysz_toschnorr(double /*nbits*/); |
| 156 | extern double keysz_toif(double /*nbits*/); |
| 157 | extern double keysz_toec(double /*nbits*/); |
| 158 | |
| 159 | /*----- That's all, folks -------------------------------------------------*/ |
| 160 | |
| 161 | #ifdef __cplusplus |
| 162 | } |
| 163 | #endif |
| 164 | |
| 165 | #endif |