Java/Security/Signature

Creating a Signature

  
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.Signature;
import java.security.interfaces.DSAParams;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.DSAPrivateKeySpec;
import java.security.spec.KeySpec;
public class Main {
  public static void main(String[] argv) throws Exception {
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
    keyGen.initialize(1024);
    KeyPair keypair = keyGen.genKeyPair();
    DSAPrivateKey privateKey = (DSAPrivateKey) keypair.getPrivate();
    DSAPublicKey publicKey = (DSAPublicKey) keypair.getPublic();
    DSAParams dsaParams = privateKey.getParams();
    BigInteger p = dsaParams.getP();
    BigInteger q = dsaParams.getQ();
    BigInteger g = dsaParams.getG();
    BigInteger x = privateKey.getX();
    BigInteger y = publicKey.getY();
    // Create the DSA key factory
    KeyFactory keyFactory = KeyFactory.getInstance("DSA");
    // Create the DSA private key
    KeySpec privateKeySpec = new DSAPrivateKeySpec(x, p, q, g);
    PrivateKey privateKey1 = keyFactory.generatePrivate(privateKeySpec);
    byte[] buffer = new byte[1024];
    Signature sig = Signature.getInstance(privateKey1.getAlgorithm());
    sig.initSign(privateKey1);
    sig.update(buffer, 0, buffer.length);
  }
}

Generate a DSA signature

 
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
public class GenSig {
  public static void main(String[] args) {
    /* Generate a DSA signature */
    if (args.length != 1) {
      System.out.println("Usage: GenSig nameOfFileToSign");
    } else
      try {
        /* Generate a key pair */
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA",
            "SUN");
        SecureRandom random = SecureRandom.getInstance("SHA1PRNG",
            "SUN");
        keyGen.initialize(1024, random);
        KeyPair pair = keyGen.generateKeyPair();
        PrivateKey priv = pair.getPrivate();
        PublicKey pub = pair.getPublic();
        /*
         * Create a Signature object and initialize it with the private
         * key
         */
        Signature dsa = Signature.getInstance("SHA1withDSA", "SUN");
        dsa.initSign(priv);
        /* Update and sign the data */
        FileInputStream fis = new FileInputStream(args[0]);
        BufferedInputStream bufin = new BufferedInputStream(fis);
        byte[] buffer = new byte[1024];
        int len;
        while (bufin.available() != 0) {
          len = bufin.read(buffer);
          dsa.update(buffer, 0, len);
        }
        ;
        bufin.close();
        /*
         * Now that all the data to be signed has been read in, generate
         * a signature for it
         */
        byte[] realSig = dsa.sign();
        /* Save the signature in a file */
        FileOutputStream sigfos = new FileOutputStream("sig");
        sigfos.write(realSig);
        sigfos.close();
        /* Save the public key in a file */
        byte[] key = pub.getEncoded();
        FileOutputStream keyfos = new FileOutputStream("suepk");
        keyfos.write(key);
        keyfos.close();
      } catch (Exception e) {
        System.err.println("Caught exception " + e.toString());
      }
  };
}

Signature Sign And Verify

 
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
import java.security.Signature;
public class MainClass {
  public static void main(String args[]) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    KeyPair keyPair = generateKeyPair(999);
    byte[] data = { 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 };
    byte[] digitalSignature = signData(data, keyPair.getPrivate());
    boolean verified;
    verified = verifySig(data, keyPair.getPublic(), digitalSignature);
    System.out.println(verified) ;
    keyPair = generateKeyPair(888);
    verified = verifySig(data, keyPair.getPublic(), digitalSignature);
    System.out.println(verified);
  }
  public static byte[] signData(byte[] data, PrivateKey key) throws Exception {
    Signature signer = Signature.getInstance("SHA1withDSA");
    signer.initSign(key);
    signer.update(data);
    return (signer.sign());
  }
  public static boolean verifySig(byte[] data, PublicKey key, byte[] sig) throws Exception {
    Signature signer = Signature.getInstance("SHA1withDSA");
    signer.initVerify(key);
    signer.update(data);
    return (signer.verify(sig));
  }
  public static KeyPair generateKeyPair(long seed) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DSA");
    SecureRandom rng = SecureRandom.getInstance("SHA1PRNG", "SUN");
    rng.setSeed(seed);
    keyGenerator.initialize(1024, rng);
    return (keyGenerator.generateKeyPair());
  }
}

Signing a Java Object

  
import java.io.Serializable;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignedObject;
public class Main {
  public static void main(String[] argv) throws Exception {
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
    keyGen.initialize(1024);
    KeyPair keypair = keyGen.genKeyPair();
    PrivateKey privateKey = keypair.getPrivate();
    PublicKey publicKey = keypair.getPublic();
    Serializable o = new MyClass();
    Signature sig = Signature.getInstance(privateKey.getAlgorithm());
    SignedObject so = new SignedObject(o, privateKey, sig);
    
    sig = Signature.getInstance(publicKey.getAlgorithm());
    boolean b = so.verify(publicKey, sig);
    o = (MyClass) so.getObject();
  }
}
class MyClass implements Serializable {
  String s = "my string";
  int i = 123;
}

Test the signature

 
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */
import java.io.FileInputStream;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
public class testSig {
  public static void main(String[] args) {
    /* Test generating and verifying a DSA signature */
    try {
      /* generate a key pair */
      KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
      keyGen.initialize(1024, new SecureRandom());
      KeyPair pair = keyGen.generateKeyPair();
      /*
       * create a Signature object to use for signing and verifying
       */
      Signature dsa = Signature.getInstance("SHA/DSA");
      /* initialize the Signature object for signing */
      PrivateKey priv = pair.getPrivate();
      dsa.initSign(priv);
      /* Update and sign the data */
      FileInputStream fis = new FileInputStream(args[0]);
      byte b;
      while (fis.available() != 0) {
        b = (byte) fis.read();
        dsa.update(b);
      }
      ;
      fis.close();
      /*
       * Now that all the data to be signed has been read in, sign it
       */
      byte[] sig = dsa.sign();
      /* Verify the signature */
      /* Initialize the Signature object for verification */
      PublicKey pub = pair.getPublic();
      dsa.initVerify(pub);
      /* Update and verify the data */
      fis = new FileInputStream(args[0]);
      while (fis.available() != 0) {
        b = (byte) fis.read();
        dsa.update(b);
      }
      ;
      fis.close();
      boolean verifies = dsa.verify(sig);
      System.out.println("signature verifies: " + verifies);
    } catch (Exception e) {
      System.err.println("Caught exception " + e.toString());
    }
  }
}

Verifies the signature for the given buffer of bytes using the public key.

  
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.interfaces.DSAParams;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.DSAPrivateKeySpec;
import java.security.spec.DSAPublicKeySpec;
import java.security.spec.KeySpec;
public class Main {
  public static void main(String[] argv) throws Exception {
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
    keyGen.initialize(1024);
    KeyPair keypair = keyGen.genKeyPair();
    DSAPrivateKey privateKey = (DSAPrivateKey) keypair.getPrivate();
    DSAPublicKey publicKey = (DSAPublicKey) keypair.getPublic();
    DSAParams dsaParams = privateKey.getParams();
    BigInteger p = dsaParams.getP();
    BigInteger q = dsaParams.getQ();
    BigInteger g = dsaParams.getG();
    BigInteger x = privateKey.getX();
    BigInteger y = publicKey.getY();
    KeyFactory keyFactory = KeyFactory.getInstance("DSA");
    KeySpec publicKeySpec = new DSAPublicKeySpec(y, p, q, g);
    PublicKey publicKey1 = keyFactory.generatePublic(publicKeySpec);
    KeySpec privateKeySpec = new DSAPrivateKeySpec(x, p, q, g);
    PrivateKey privateKey1 = keyFactory.generatePrivate(privateKeySpec);
    byte[] buffer = new byte[1024];
    Signature sig = Signature.getInstance(privateKey1.getAlgorithm());
    sig.initSign(privateKey1);
    sig.update(buffer, 0, buffer.length);
    byte[] signature = sig.sign();
    sig = Signature.getInstance(publicKey1.getAlgorithm());
    sig.initVerify(publicKey1);
    sig.update(buffer, 0, buffer.length);
    sig.verify(signature);
  }
}

Verify a DSA signature

 
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.X509EncodedKeySpec;
public class VerSig {
  public static void main(String[] args) {
    /* Verify a DSA signature */
    if (args.length != 3) {
      System.out
          .println("Usage: VerSig publickeyfile signaturefile datafile");
    } else
      try {
        /* import encoded public key */
        FileInputStream keyfis = new FileInputStream(args[0]);
        byte[] encKey = new byte[keyfis.available()];
        keyfis.read(encKey);
        keyfis.close();
        X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encKey);
        KeyFactory keyFactory = KeyFactory.getInstance("DSA", "SUN");
        PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);
        /* input the signature bytes */
        FileInputStream sigfis = new FileInputStream(args[1]);
        byte[] sigToVerify = new byte[sigfis.available()];
        sigfis.read(sigToVerify);
        sigfis.close();
        /*
         * create a Signature object and initialize it with the public
         * key
         */
        Signature sig = Signature.getInstance("SHA1withDSA", "SUN");
        sig.initVerify(pubKey);
        /* Update and verify the data */
        FileInputStream datafis = new FileInputStream(args[2]);
        BufferedInputStream bufin = new BufferedInputStream(datafis);
        byte[] buffer = new byte[1024];
        int len;
        while (bufin.available() != 0) {
          len = bufin.read(buffer);
          sig.update(buffer, 0, len);
        }
        ;
        bufin.close();
        boolean verifies = sig.verify(sigToVerify);
        System.out.println("signature verifies: " + verifies);
      } catch (Exception e) {
        System.err.println("Caught exception " + e.toString());
      }
    ;
  }
}