Re: [xacml] Attribute validation

[sampo@symlabs.com]

Anil Tappetla (atappetl) wrote:
> Assuming the PEP uses digital signatures in SAML wrapped XACML (or for
> that matter SSL) as a means to authenticate with the PDP and to protect
> the integrity of the request, would it ever be a possible case where the
> attributes in the request have not been validated as legitimate by the
> PEP ? The signature only establishes the authenticity and integrity, but
> the requestor makes no claims about the validity of the attributes. In
> such cases, should not the PDP make these validations in order to
> circumvent a possible security attack ?

There is not much point in PEP supplying attributes if it does not
guarantee their authenticity. If PEP is unable to supply authentic
attributes, then PDP/PIP would be better off obtaining the attributes
directly from the authorative source rather than "validate".

I can see a situation where user lands to PEP using SSO that passes
some attributes from IdP. The SSO a7n is signed so authenticity
of attributes can be validated by checking the signature. However,
generally the signature can only be checked by PEP and will not
be visible to PDP. Thus PEP unwraps the attributes and then vouches
their authenticity to the PDP. It would be nice if the IdP signature
was not lost and could be passed to the PDP so PDP would be
trusting the IdP rather than PEP.

While it would be possible to sign the a7n in such a way that the
attribute statement could be extracted without breaking the signature,
the XACML attribute formatting is different. Perhaps XACML should
use SAML Attribute Statements as the format for attributes? Barring that,
the only way I can see this could be done right now is to pass
at XACML layer one big attribute whose contents would be the
signed a7n or attribute statement.

Cheers,
--Sampo

> Regards,
> Anil
>