PROBLEM

When attempting to decrypt the SAML response from IdP, the following exception occurs:-

org.apache.xml.security.encryption.XMLEncryptionException: Illegal key size
Original Exception was java.security.InvalidKeyException: Illegal key size
	at org.apache.xml.security.encryption.XMLCipher.decryptToByteArray(XMLCipher.java:1822)
	at org.opensaml.xml.encryption.Decrypter.decryptDataToDOM(Decrypter.java:596)
	at org.opensaml.xml.encryption.Decrypter.decryptUsingResolvedEncryptedKey(Decrypter.java:795)
	at org.opensaml.xml.encryption.Decrypter.decryptDataToDOM(Decrypter.java:535)
	at org.opensaml.xml.encryption.Decrypter.decryptDataToList(Decrypter.java:453)
	at org.opensaml.xml.encryption.Decrypter.decryptData(Decrypter.java:414)
	at org.opensaml.saml2.encryption.Decrypter.decryptData(Decrypter.java:141)
	at org.opensaml.saml2.encryption.Decrypter.decrypt(Decrypter.java:69)
	at org.springframework.security.saml.websso.WebSSOProfileConsumerImpl.processAuthenticationResponse(WebSSOProfileConsumerImpl.java:199)
	at org.springframework.security.saml.SAMLAuthenticationProvider.authenticate(SAMLAuthenticationProvider.java:82)

SOLUTION

When inspecting the SAML response payload below, the data is encrypted with AES-256:-

<?xml version="1.0" encoding="UTF-8"?>
<samlp:Response
        Consent="urn:oasis:names:tc:SAML:2.0:consent:unspecified"
        Destination="https://server/my-app/saml/SSO"
        ID="_370d6ba5-177c-494b-9147-2eafd9ecb6c9"
        InResponseTo="a5c5dja1i5fgb2bf2e66f6g9g5398gj"
        IssueInstant="2016-02-18T15:28:43.473Z" Version="2.0" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">
    <Issuer xmlns="urn:oasis:names:tc:SAML:2.0:assertion">http://adfs-server/adfs/services/trust</Issuer>
    <samlp:Status>
        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
    </samlp:Status>
    <EncryptedAssertion xmlns="urn:oasis:names:tc:SAML:2.0:assertion">
        <xenc:EncryptedData Type="http://www.w3.org/2001/04/xmlenc#Element" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
            <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes256-cbc"/>
            <KeyInfo xmlns="http://www.w3.org/2000/09/xmldsig#">
                <e:EncryptedKey xmlns:e="http://www.w3.org/2001/04/xmlenc#">
                    <e:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p">
                        <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
                    </e:EncryptionMethod>
                    <KeyInfo>
                        <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
                            <ds:X509IssuerSerial>
                                <ds:X509IssuerName>CN=server</ds:X509IssuerName>
                                <ds:X509SerialNumber>1822784706</ds:X509SerialNumber>
                            </ds:X509IssuerSerial>
                        </ds:X509Data>
                    </KeyInfo>
                    <e:CipherData>
                        <e:CipherValue>isG83fVk50fJRIcg...</e:CipherValue>
                    </e:CipherData>
                </e:EncryptedKey>
            </KeyInfo>
            <xenc:CipherData>
                <xenc:CipherValue>+b2o6HNxaxsse7rkB...</xenc:CipherValue>
            </xenc:CipherData>
        </xenc:EncryptedData>
    </EncryptedAssertion>
</samlp:Response>

By default, Java’s keysize is limited to 128-bit key due to US export laws and a few countries’ import laws.

To fix this…

• Determine the Java version.
• Download Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files – Java 7 or Java 8.
• Inflate the zip file.
• Copy local_policy.jar and US_export_policy.jar to [JAVA_HOME]/jre/lib/security.

… and I’ll begin to write shitty code from this day forward…