OpenSAML user discussion

Hi to all

i'm an university student and i'm developing a project that need to use some 
SAML component. In particular i've choose openSAML 1.1b for the java side; 
after i have create the build directory and have included the classes in my 
project i have installed all required jars:

-xmlsec.jar
-log4j-1.2.15.jar
-xalan.jar

I've created a simple java application with just a main that take a 
certificate from file (standard X.509) and simply populate a SAMLAssertion 
object. It all works without problem untill i try to sign the assertion. I 
report here the exception:

##################################################################################
Exception in thread "main" 
org.apache.xml.security.signature.XMLSignatureException: The requested 
algorithm http://www.w3.org/2000/09/xmldsig#rsa-sha1 does not exist. Original 
Message was: null
Original Exception was java.lang.NullPointerException
        at org.opensaml.SAMLSignedObject.sign(Unknown Source)
        at MappingAssertion.main(MappingAssertion.java:211)
Caused by: org.apache.xml.security.signature.XMLSignatureException: The 
requested algorithm http://www.w3.org/2000/09/xmldsig#rsa-sha1 does not 
exist. Original Message was: null
Original Exception was java.lang.NullPointerException
        at 
org.apache.xml.security.algorithms.SignatureAlgorithm.<init>(SignatureAlgorithm.java:148)
        at 
org.apache.xml.security.signature.SignedInfo.<init>(SignedInfo.java:154)
        at 
org.apache.xml.security.signature.XMLSignature.<init>(XMLSignature.java:236)
        at 
org.apache.xml.security.signature.XMLSignature.<init>(XMLSignature.java:214)
        ... 2 more
##################################################################################

here there is a part of code and the line (the last) that generate the 
exception:

##################################################################################
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();
                        
                        ArrayList nuova=new ArrayList();
                        nuova.add(cert);
                        
                        
asr.sign(XMLSignature.ALGO_ID_SIGNATURE_RSA_SHA1,MessageDigestAlgorithm.ALGO_ID_DIGEST_SHA1,
 priv, nuova);
##################################################################################
              
XMLSignature and MessageDigestAlgorithm are classes included in the xmlsec 
jar. I think it was a problem of cunfigurantion but after looking in the 
config.xml of xmlsec jar i havent' found problem so i have not modifying 
nothing.

To develop this software i'm using 

Eclipse SDK
Version: 3.4.0
Build id: I20080617-2000
with
java version "1.5.0_16"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_16-b02)
Java HotSpot(TM) Client VM (build 1.5.0_16-b02, mixed mode)
installed on Windows Vista

I've read the SAML specification but about the use of XML Signature i'm new.
What can i do to solve my problem? Any suggestion.

Thank you very much for your help.

Best Regards
Omar Cavagna

PS for any informations tell me and sorry for my bad english.