Validate IDP initiated SAML2.0 Response

Question

SAML experts please help!!!!

Am very new to SAML and JSP. I wanna validate a IDP(identity provider) initiated SAML response token using Opensaml library in java(Environment linux,Tomcat6.0) and retrieve the Attribute information sent such as userid,username,email.The SAML response is not encrypted and i have the idp's trust certificate installed in my java keystore.The SAML token profile is "web browser SSO" and it uses HTTP-POST Binding.The certificate has a public key in it.Do i need a private key to validate?What are the steps to be done for a succesful validation?Just a digital signature validation is enough to trust the source?Should i do profile validation or something else? Below given is the SAML Response i will be receiving from the IDP. Please let me know if you need any more information?Sorry if i did not give enough information.Please help me...Thanks in advance.

<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" ID="XYZ" Version="2.0" IssueInstant="2013-07-10T16:43:54Z" Destination="http://www.testsp.com">
  <saml:Issuer xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">http://www.testidp.com:8080/opensso</saml:Issuer> 
- <samlp:Status xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">
  <samlp:StatusCode xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" Value="urn:oasis:names:tc:SAML:2.0:status:Success" /> 
  </samlp:Status>
- <saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" ID="xyz" IssueInstant="2013-07-10T16:43:51Z" Version="2.0">
  <saml:Issuer>http://www.testidp.com:8080/opensso</saml:Issuer> 
- <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
- <ds:SignedInfo>
  <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" /> 
  <ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" /> 
- <ds:Reference URI="#xyz">
- <ds:Transforms>
  <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /> 
  <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" /> 
  </ds:Transforms>
  <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" /> 
  <ds:DigestValue>...hdfb3454jh545dfbj545423df....=</ds:DigestValue> 
  </ds:Reference>
  </ds:SignedInfo>
  <ds:SignatureValue>..................hsdgysgdyyusgfdfb98738e43hjrg874y474h7y8r............=</ds:SignatureValue> 
- <ds:KeyInfo>
- <ds:X509Data>
  <ds:X509Certificate>............./KPm0qLP8vCOhyI76AUE6jL NFeTlcAe3B6hOdfKCiu+EtHeZC2i/8jf1rHDNPey4TS1MQj/.......
</ds:X509Certificate> 
  </ds:X509Data>
  </ds:KeyInfo>
  </ds:Signature>
- <saml:Subject>
  <saml:NameID Format="urn:oasis:names:tc:SAML:2.0:nameid-format:transient" NameQualifier="http://www.testidp.com:8080/opensso" SPNameQualifier="http://www.testsp.com">....Zeq8NhJKRKDXUwx67ytuynwj4n...</saml:NameID> 
- <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
  <saml:SubjectConfirmationData NotOnOrAfter="2013-07-10T16:53:51Z" Recipient="http://www.testsaml.com/tespsamlmodule" /> 
  </saml:SubjectConfirmation>
  </saml:Subject>
- <saml:Conditions NotBefore="2013-07-10T16:33:51Z" NotOnOrAfter="2013-07-10T16:53:51Z">
- <saml:AudienceRestriction>
  <saml:Audience>http://www.testsaml.com/tespsamlmodule</saml:Audience> 
  </saml:AudienceRestriction>
  </saml:Conditions>
- <saml:AuthnStatement AuthnInstant="2013-07-10T16:36:35Z" SessionIndex="......erer54t54y45y75666y65y65y....">
- <saml:AuthnContext>
  <saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml:AuthnContextClassRef> 
  </saml:AuthnContext>
  </saml:AuthnStatement>
- <saml:AttributeStatement>
- <saml:Attribute Name="UID">
  <saml:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">ab123</saml:AttributeValue> 
  </saml:Attribute>
- <saml:Attribute Name="uname">
  <saml:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">robert</saml:AttributeValue> 
  </saml:Attribute>
- <saml:Attribute Name="EmailAddress">
  <saml:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">[email protected]</saml:AttributeValue> 
  </saml:Attribute>
  </saml:AttributeStatement>
  </saml:Assertion>
  </samlp:Response>

Answer 1

You need to validate the responce according to the SAML spec. There are some functionaliy for doing this in OpenSAML but i seems the safest bet is to write your own validation code. see. http://marc.info/?t=137354098500007&r=1&w=2

You must also validate signature. As with all signature verification you use the public key. Here is some I wrote on my blog about OpenSAML signatur verification. http://mylifewithjava.blogspot.no/2012/11/verifying-signatures-with-opensaml.html

I have more on signing and encryption using OpenSAML in my book, A Guide to OpenSAML