http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
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package org.bouncycastle.crypto.tls;

import org.bouncycastle.crypto.CryptoException;
import org.bouncycastle.crypto.Signer;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;

public interface TlsSigner
{
    void init(TlsContext context);

    byte[] generateRawSignature(AsymmetricKeyParameter privateKey, byte[] md5AndSha1)
        throws CryptoException;

    byte[] generateRawSignature(SignatureAndHashAlgorithm algorithm,
        AsymmetricKeyParameter privateKey, byte[] hash)
        throws CryptoException;

    boolean verifyRawSignature(byte[] sigBytes, AsymmetricKeyParameter publicKey, byte[] md5AndSha1)
        throws CryptoException;

    boolean verifyRawSignature(SignatureAndHashAlgorithm algorithm, byte[] sigBytes,
        AsymmetricKeyParameter publicKey, byte[] hash)
        throws CryptoException;

    Signer createSigner(AsymmetricKeyParameter privateKey);

    Signer createSigner(SignatureAndHashAlgorithm algorithm, AsymmetricKeyParameter privateKey);

    Signer createVerifyer(AsymmetricKeyParameter publicKey);

    Signer createVerifyer(SignatureAndHashAlgorithm algorithm, AsymmetricKeyParameter publicKey);

    boolean isValidPublicKey(AsymmetricKeyParameter publicKey);
}