Hello,
Could you guys be kind enough to let me know how one would initialize
the Verifier in the validation application in a way no private
exponent is required?
The following code example is in fact working for both signing and
verifying but I need to use AssignFrom which imply using the private
key!
My initial idea was to only use the decode point G(x, y) as a public
element. This does not seem to be working
as if I remove the following lines :
// create a public key from the private key
PublicKey.AssignFrom(PrivateKey);
The verification crashes. Looking at AssignFrom() shows that indeed it
seems public key is created using the
private exponent.
Should I then export the whole PublicKey? This probably means the
public material is going to be bigger.
Maybe all this makes sense for you guys. It does not on my side.
I thought that using PublicKey.SetPublicElement(newPoint); would be
enough but it seems not to go that way.
Thank you very much!
Arnaud
Code snippet ( not the the signing and verifying is omitted as it does
not seem to be the problem here ) :
------------------------------------------------------------------------------------------------------------------------------------------------------
CryptoPP::ECDSA< CryptoPP::ECP >::PrivateKey PrivateKey;
// initialize the private key from a now certicom curve
PrivateKey.AccessGroupParameters().Initialize( CryptoPP::ASN1::secp521r1() );
// set the the private exponent
PrivateKey.SetPrivateExponent(CryptoPP::Integer("147088163948218050")); //
This is the actual private key
// set up the signer mechanism
CryptoPP::ECDSA< CryptoPP::ECP >::Signer signer(PrivateKey);
// get the encoded curve point size then allocate and zero some
memory for it
int encodedpointsize =
PrivateKey.GetGroupParameters().GetCurve().EncodedPointSize(true);
byte *pointb = new byte[encodedpointsize];
memset(pointb, 0, encodedpointsize);
// allocate a create a public key strcuture
CryptoPP::ECDSA< CryptoPP::ECP >::PublicKey PublicKey;
// create a public key from the private key
PublicKey.AssignFrom(PrivateKey);
// actual place the encoded ec point into our buffer
PrivateKey.GetGroupParameters().GetCurve().EncodePoint(pointb,
PublicKey.GetPublicElement(), true);
// initialize the public key
PublicKey.AccessGroupParameters().Initialize(CryptoPP::ASN1::secp521r1());
// create a temporary point
CryptoPP::ECP::Point newPoint;
PublicKey.GetGroupParameters().GetCurve().DecodePoint(newPoint,
pointb, encodedpointsize);
PublicKey.SetPublicElement(newPoint);
// free memory
delete pointb;
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