test/jdk/java/security/Signature/SignWithOutputBuffer.java

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/*
 * @test
 * @bug 4114896
 * @summary Signature should support a sign() method that places the signature
 * in an already existing array.
 * @run main SignWithOutputBuffer DSS 512
 * @run main SignWithOutputBuffer SHA256withDSA 2048
 */

import java.security.*;

public class SignWithOutputBuffer {

    public static void main(String[] args) throws Exception {

        int numBytes;

        String kpgAlgorithm = "DSA";
        int keySize = Integer.parseInt(args[1]);
        KeyPairGenerator kpGen = KeyPairGenerator.getInstance(kpgAlgorithm);
        kpGen.initialize(keySize);
        KeyPair kp = kpGen.genKeyPair();

        String signAlgo = args[0];
        Signature sig = Signature.getInstance(signAlgo);
        sig.initSign(kp.getPrivate());
        sig.update((byte)0xff);

        // Allocate buffer for signature. According to BSAFE, the size of the
        // signature may be as many as 48 bytes.
        // First, let's allocate a buffer that's too short.
        byte[] out = new byte[10];
        try {
            numBytes = sig.sign(out, 0, out.length);
        } catch (SignatureException e) {
            System.out.println(e);
        }

        // Now repeat the same with a buffer that's big enough
        sig = Signature.getInstance(signAlgo);
        sig.initSign(kp.getPrivate());
        sig.update((byte)0xff);
        out = new byte[64];
        numBytes = sig.sign(out, 0, out.length);

        System.out.println("Signature len="+numBytes);
    }
}