text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2014 The Bitcoin developers
  // Copyright (c) 2017 The INDIUM 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
  