Well, I figured out that adding "a %= p; b %= p; x %= p; y %= p;" to
my source code after the curve I had commented out makes it work (idea
from
http://www.codeproject.com/cpp/ECIESProductKey.asp?df=100&forumid=359069&exp=0&select=1780315).
But what worries me is that even though it looks like it's working,
signer.GetKey().GetPrivateExponent() returns 1, which seems
suspicious, because if I use the standard ASN1::secp112r1() curve,
signer.GetKey().GetPrivateExponent() returns a huge number. Can
anyone explain why this would be or what the Private Exponent is
supposed to represent (appears to be the value of h)?
Actually, if I just replace h with x in the call to Initialize, it
still seems to work and I get x back from the call to
signer.GetKey().GetPrivateExponent(). But x is already used in the
point G, so... what is h for? This is so confusing.
Here's the new top part of the source code:
CryptoPP::Integer p("147088164709569533");
CryptoPP::Integer a("6094329446842148");
CryptoPP::Integer b("-57162508610850246");
CryptoPP::Integer n("147088163948218061"); // R from ECB
CryptoPP::Integer h("1"); // S from ECB, must be
<= 4
CryptoPP::Integer x("71002669261090523");
CryptoPP::Integer y("11469141678568184");
a %= p; b %= p; x %= p; y %= p;
CryptoPP::ECP ec( p, a, b );
CryptoPP::ECP::Point G( x, y );
CryptoPP::ECDSA< CryptoPP::ECP >::PrivateKey PrivateKey;
PrivateKey.Initialize( ec, G, n, h );
CryptoPP::ECDSA< CryptoPP::ECP >::Signer signer(PrivateKey);
std::cout << "Private Key x = " <<
signer.GetKey().GetPrivateExponent() << "\r\n";
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