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The content (or attribute value) of the eduPersonTargetedID attribute is defined to be a SAML 2.0 persistent NameID, i.e., an XML structure that's logically a 3-tuple. This data structure is sometimes called a "long-lived service-specific pseudonym" in that it's a stable and opaque identifier that differs for each service a subject is accessing. So Service A and Service B cannot profile (or match) subjects based on the identifier value alone, as each service will know the subject by a different NameID value.

Issues

• All forms of eduPersonTargetedID attribute as well as all forms of the SAML 2.0 persistent NameID itself suffer from a case folding issue (due to their use of the base64 encoding) that may lead to identifier collisions at Service Providers not treating identifiers as case-sensitive. Consider this an informal Security Advisory against any use of this attribute (or persistent NameIDs in general).
• saml2int – the Interoperable SAML 2.0 Deployment Profile, a normative part of eduID.at via the eduID.at Technical Profile – states in Version 0.2 that persistent NameIDs should be transmitted in the Subject of the SAML Assertion, not as an eduPersonTargetedID Attribute (value). So use of eduPersonTargetedID within eduID.at actually constitutes a formal policy violation.
• Also note that the new version of saml2int goes much farther and states that:

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