Chaum blind signature

Question

Hello,
I'm trying to implement the chaum blind signature using java.security.Signature
Signature sig = Signature.getInstance("MD5WithRSA");
sig.initSign(Main.prvk);
sig.update(mesageCB.getTokenBlinded().toByteArray());
byte[] tokenSig = sig.sign();
but when I tryed to get the signed token, from the blinded signed token my signature won't validate anymore. So I printed
BigInteger d=((RSAPrivateCrtKeyImpl)Main.prvk).getPrivateExponent();
BigInteger e=((RSAPrivateCrtKeyImpl)Main.prvk).getPublicExponent();
BigInteger n=((RSAPrivateCrtKeyImpl)Main.prvk).getModulus();
"mesajCB.gettokenOrbit().modPow(d,n)" and it's difrent from
"new BigInteger(tokenSig)"
Is that normal? How is the rsa signature implemented? How can I get my blind signature to work using java.security.Signature.
Thank you, and I apologise for my bad english!

Answer 1

Hi, I'm implementing a blind signature service as well. In your code you use MD5WithRSA algorithm to sign the message, the result is different from
mesajCB.gettokenOrbit().modPow(d,n) because here you're signing the message without hashing it with MD5 algorithm.