CKey::Check question #4918

Is there any place/doc to explain what is below for?

bool CKey::Check(const unsigned char *vch) { // Do not convert to OpenSSL's data structures for range-checking keys, // it's easy enough to do directly. static const unsigned char vchMax[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 }; bool fIsZero = true; for (int i=0; i<32 && fIsZero; i++) if (vch[i] != 0) fIsZero = false; if (fIsZero) return false; for (int i=0; i<32; i++) { if (vch[i] < vchMax[i]) return true; if (vch[i] > vchMax[i]) return false; } return true; }

It does a simple range check. Only keys 1..vchMax are valid. I suggest reading the version in git master, which is much easier to understand.

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

thx, but my original meaning is "why does vchMaxModOrder define look likes a serial magic value"? what's '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" meaning?

vchMaxModOrder is the order of secp256k1's generator (n), so is the maximum valid key value.

To be entirely correct, it is the order minus one, and the range check performs a greater-than check. Valid values for r and s in the signature are in the range 1..(order-1), inclusive.