In those places where SAML statements are used, RPs will generally be unable to validate signatures on the SAML statement, either because the signature has been stripped off by the IdP or because the RP is unable to validate the binding between the signer, the key used to sign, and the realm represented by the IdP. For these reasons, it is required that IdPs do the necessary trust checking on the SAML statements and that RPs can trust the AAA infrastructure to keep the SAML statements valid.