Carrying sensitive information in SAML assertions
When SAML is used in conjunction with WS-Security, only an small piece of the token is encrypted, the proof key for the relying party. The rest of the token goes in plain text, that also includes the user's claims.
<saml:Conditions NotBefore="2009-02-24T19:48:20.500Z" NotOnOrAfter="2009-02-24T19:53:20.500Z"></saml:Conditions>
<saml:Attribute AttributeName="displayName" AttributeNamespace="http://schemas.microsoft.com/xsi/2005/05/role">
<saml:AttributeValue>John Foo</saml:AttributeValue> <--Attribute value-->
Knowing this, you should never include sensitive information as claims in a SAML token. This is also related to the identity law #2, "Minimal Disclosure for a Constrained Use". The Identity provider should only disclose the least amount of identifiying information for executing the operation on the relying party.
Some examples are,
- A winery only needs to know whether the customer is in a legal age for buying alcohol according to the law, a claim like "over21" should be enough for that purpose, there is not need to know the customer birth date at all.
- An online store that sells products does not necessary need to know the number of every credit card owned by a customer, a friendly name representing the card and optionally the available balance could be enough for completing a purchase.
SAML 2.0 introduces the concept of "encrypted attribute", which clearly states its purpose, encrypt individual assertions in a SAML token. In this way, a token can now carry the encrypted proof key and optionally one or more encrypted assertions with sensitive information.
You can take a look at this page for more information about the differences between SAML 1.1 and 2.0.
Geneva Framework Beta 1 already implements a subset of SAML 2.0, however, it looks like this feature has been left out in the current release. Not sure either whether this feature will be included as part of the final release (Last quarter of 2009). I created a post in the forums some time ago, I haven't received any feedback yet.