Java Tutorial/Security/Public Key Cryptography Standards

Basic class for exploring PKCS #1 V1.5 Signatures.

   <source lang="java">

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()));
 }

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