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annotate libtommath/bn_mp_sub.c @ 1659:d32bcb5c557d

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Add Ed25519 support (#91) * Add support for Ed25519 as a public key type Ed25519 is a elliptic curve signature scheme that offers better security than ECDSA and DSA and good performance. It may be used for both user and host keys. OpenSSH key import and fuzzer are not supported yet. Initially inspired by Peter Szabo. * Add curve25519 and ed25519 fuzzers * Add import and export of Ed25519 keys
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Wed, 11 Mar 2020 21:09:45 +0500
parents f52919ffd3b1
children 1051e4eea25a
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_SUB_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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4 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * SPDX-License-Identifier: Unlicense
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13 */
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14
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15 /* high level subtraction (handles signs) */
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16 int mp_sub(const mp_int *a, const mp_int *b, mp_int *c)
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17 {
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18 int sa, sb, res;
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19
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20 sa = a->sign;
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21 sb = b->sign;
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22
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23 if (sa != sb) {
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24 /* subtract a negative from a positive, OR */
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25 /* subtract a positive from a negative. */
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26 /* In either case, ADD their magnitudes, */
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27 /* and use the sign of the first number. */
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28 c->sign = sa;
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29 res = s_mp_add(a, b, c);
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30 } else {
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31 /* subtract a positive from a positive, OR */
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32 /* subtract a negative from a negative. */
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33 /* First, take the difference between their */
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34 /* magnitudes, then... */
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35 if (mp_cmp_mag(a, b) != MP_LT) {
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36 /* Copy the sign from the first */
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37 c->sign = sa;
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38 /* The first has a larger or equal magnitude */
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39 res = s_mp_sub(a, b, c);
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40 } else {
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41 /* The result has the *opposite* sign from */
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42 /* the first number. */
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43 c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
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44 /* The second has a larger magnitude */
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45 res = s_mp_sub(b, a, c);
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46 }
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47 }
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48 return res;
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49 }
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51 #endif
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52
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53 /* ref: HEAD -> master, tag: v1.1.0 */
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54 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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55 /* commit time: 2019-01-28 20:32:32 +0100 */