PKCS#1 digital signature

PKCSSigner.java

private byte[] sign(byte[] data, PrivateKey privateKey) throws GeneralSecurityException {

        Security.addProvider(new BouncyCastleProvider());
        
        Signature signer = Signature.getInstance("SHA1withRSA", "BC");
        signer.initSign(privateKey);
        signer.update(data);
        return signer.sign();

}

PKCSSignerDetached.java

public byte[] signWithExternDigest(byte[] data, PrivateKey privateKey) throws GeneralSecurityException, IOException {

        AlgorithmIdentifier sha1AlgoId = new AlgorithmIdentifier(new ASN1ObjectIdentifier("1.3.14.3.2.26"));
        DigestInfo digestInfo = new DigestInfo(sha1AlgoId, data);
        byte[] paddedDigest = digestInfo.getEncoded("DER");

        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "BC");
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);
        return cipher.doFinal(paddedDigest);
}