// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2015 The Bitcoin Core 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
