eccryptoverify.cpp

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include "eccryptoverify.h"

namespace
{
int CompareBigEndian(const unsigned char* c1, size_t c1len, const unsigned char* c2, size_t c2len)
{
    while (c1len > c2len) {
        if (*c1)
            return 1;
        c1++;
        c1len--;
    }
    while (c2len > c1len) {
        if (*c2)
            return -1;
        c2++;
        c2len--;
    }
    while (c1len > 0) {
        if (*c1 > *c2)
            return 1;
        if (*c2 > *c1)
            return -1;
        c1++;
        c2++;
        c1len--;
    }
    return 0;
}

/** Order of secp256k1's generator minus 1. */
const unsigned char vchMaxModOrder[32] = {
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE,
    0xBA, 0xAE, 0xDC, 0xE6, 0xAF, 0x48, 0xA0, 0x3B,
    0xBF, 0xD2, 0x5E, 0x8C, 0xD0, 0x36, 0x41, 0x40};

/** Half of the order of secp256k1's generator minus 1. */
const unsigned char vchMaxModHalfOrder[32] = {
    0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0x5D, 0x57, 0x6E, 0x73, 0x57, 0xA4, 0x50, 0x1D,
    0xDF, 0xE9, 0x2F, 0x46, 0x68, 0x1B, 0x20, 0xA0};

const unsigned char vchZero[1] = {0};
} // anon namespace

namespace eccrypto
{
bool Check(const unsigned char* vch)
{
    return vch &&
           CompareBigEndian(vch, 32, vchZero, 0) > 0 &&
           CompareBigEndian(vch, 32, vchMaxModOrder, 32) <= 0;
}

bool CheckSignatureElement(const unsigned char* vch, int len, bool half)
{
    return vch &&
           CompareBigEndian(vch, len, vchZero, 0) > 0 &&
           CompareBigEndian(vch, len, half ? vchMaxModHalfOrder : vchMaxModOrder, 32) <= 0;
}

} // namespace eccrypto