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Basic class for exploring PKCS #1 V1 5 Signatures

import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.MessageDigest; import java.security.SecureRandom; import java.security.Security; import java.security.Signature; import javax.crypto.Cipher; import org.bouncycastle.asn1.ASN1InputStream; import org.bouncycastle.asn1.ASN1OctetString; import org.bouncycastle.asn1.ASN1Sequence; import org.bouncycastle.asn1.util.ASN1Dump; public class MainClass {   public static void main(String[] args) throws Exception {     Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());     KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA", "BC");     keyGen.initialize(512, new SecureRandom());     KeyPair keyPair = keyGen.generateKeyPair();     Signature signature = Signature.getInstance("SHA256withRSA", "BC");     signature.initSign(keyPair.getPrivate());     byte[] message = "abc".getBytes();     signature.update(message);     byte[] sigBytes = signature.sign();     Cipher cipher = Cipher.getInstance("RSA/None/PKCS1Padding", "BC");     cipher.init(Cipher.DECRYPT_MODE, keyPair.getPublic());     byte[] decSig = cipher.doFinal(sigBytes);     ASN1InputStream aIn = new ASN1InputStream(decSig);     ASN1Sequence seq = (ASN1Sequence) aIn.readObject();     System.out.println(ASN1Dump.dumpAsString(seq));     MessageDigest hash = MessageDigest.getInstance("SHA-256", "BC");     hash.update(message);     ASN1OctetString sigHash = (ASN1OctetString) seq.getObjectAt(1);     System.out.println(MessageDigest.isEqual(hash.digest(), sigHash.getOctets()));   } }