package civitas.crypto.signature;
   
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Controller;
   
   import civitas.crypto.messagedigest.CryptoHash;
   import civitas.crypto.parameters.ElGamalParameters;
   import civitas.crypto.signedciphertext.ElGamalSignedCiphertext;
   import civitas.util.CivitasBigInteger;
  
  @Controller
  public class VerifyElGamalSignature {
  	@Autowired
  	CryptoHash cryptoHash;
  
  	public boolean apply(
  			final ElGamalParameters params, final ElGamalSignedCiphertext ciphertext, final byte[] additionalEnv) {
  		CivitasBigInteger x = params.g
  				.modPow(ciphertext.d.mod(params.q), params.p)
  				.modMultiply(ciphertext.a.modPow(ciphertext.c.modNegate(params.q), params.p), params.p);
  		CivitasBigInteger v =
  				cryptoHash.apply(x, ciphertext.a, ciphertext.b, additionalEnv).mod(params.q);
  		return ciphertext.c.equals(v);
  	}
  
  	public boolean apply(final ElGamalParameters params, final ElGamalSignedCiphertext ciphertext) {
  		return apply(params, ciphertext, null);
  	}
  }