RSA PSS Signature scheme

Question

Hi,
I am working on digital signatures RSA. I have two issues/doubts :-D
1) In Java 1.5, the crypto specification talks abt API support for RSA PKCS using PKCS #1 v2.1 thru the PSS padding scheme for signatures - java.security.spec.PPSParameterSpec. So, how i understood it was, after i create signature object for RSA i have to use setParameter to set these PSSParameterSpec to my signature object. But when i run my code, i get the UnSupportedOperationException. Please help me in this regard.
The Exception message is
java.lang.UnsupportedOperationException
at java.security.SignatureSpi.engineSetParameter(SignatureSpi.java:306)
at java.security.Signature$Delegate.engineSetParameter(Signature.java:11
61)
at java.security.Signature.setParameter(Signature.java:794)
at rsapsSigning.main(rsapsSigning.java:22)
My source code for the same is:
public class rsapsSigning
     public static void main(String a[])
          try
               String datafile = "C:\\old.txt";
               PSSParameterSpec pss = PSSParameterSpec.DEFAULT;
               Signature s = Signature.getInstance("SHA1withRSA");
               /*initialise sugnature object with pss parameter for RSA*/
               s.setParameter((AlgorithmParameterSpec)pss); //exception gets thrown at this point
               KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
               kpg.initialize(128); // 128 is the keysize.
          KeyPair kp = kpg.generateKeyPair();
          PublicKey pubk = kp.getPublic();
          PrivateKey prvk = kp.getPrivate();
               s.initSign(prvk);
               FileInputStream fis = new FileInputStream(datafile);
          byte[] dataBytes = new byte[1024];
          int nread = fis.read(dataBytes);
          while (nread > 0) {
          s.update(dataBytes, 0, nread);
          nread = fis.read(dataBytes);
          byte[] sig = s.sign();
          for(int i = 0;i <sig.length;i++)
               System.out.println(sig);
     }catch(Exception e)
          e.printStackTrace();
2) One other method that i tried was, instead of using PSSParameterSpec class, while creating Signature object, crypto Spec of 1.5 talks abt the usage of "<digest>with<encryptionalgo>and<mgf>" in the getInstance() of Signature class. So going on these lines, i can as well give "SHA1withRSAandMGF1" which is precisely what has been described as the default value for RSA PSS. But when i give so directly, I get "NoSuchAlgorithmException". In fact, for a trial basis when i tried "MD5withSHA1andMGF1" (the example given in the crypto spec of 1.5) also, i get the same exception :-( :-(
java.security.NoSuchAlgorithmException: SHA1withRSAandMGF1 Signature not availab
le
at java.security.Signature.getInstance(Signature.java:208)
at pp.main(pp.java:18)
My code for this is:
public class pp
     public static void main(String a[])
          try
               String datafile = "C:\\new.txt";
               Signature s = Signature.getInstance("SHA1withRSAandMGF1"); //exception gets thrown here
               System.out.println("SHA1withRSAandMGF1");
catch(Exception e)
e.printStackTrace();
I am sorry that my query seems so long. But i was just trying to tell all the cases that I have tried.
I would be grateful to any suggestions.
Best Rgds

Answer 1

Hi Stark,
Exactly....Even my list of signatures does not return anything with PSS. Like how you said may be there is no engine support. But is there any workaround for this??? How can i use PSS with RSA in Java 1.5??? Any idea??
And also in the JCE Crypto Spec, it is given that "For the new signature schemes defined in PKCS #1 v 2.0, for which the <digest>with<encryption> form is insufficient, <digest>with<encryption>and<mgf> can be used to form a name. Here, <mgf> should be replaced by a mask generation function such as MGF1. Example: MD5withRSAandMGF1. " but this also is not displayed in the list of signatures. Am I wrong in my understanding or over looking something or is it that java 5 has not yet started supporting if signature algos are given in this format. Any idea here too ??