Certificate Extensions and Attributes Supporting Authentication in Point-to-Point Protocol (PPP) and Wireless Local Area Networks (WLAN)
obsoletes
- rfc-3770 — Certificate Extensions and Attributes Supporting Authentication in Point-to-Point Protocol (PPP) and Wireless Local Area Networks (WLAN)
Extracted elements (20)
A companion attribute certificate carrying the SSID list is provided as an alternative when the public key certificate itself cannot be modified, allowing SSID association without reissuing the base certificate.
Certificate extensions identifying the intended environment (PPP vs. WLAN, specific SSIDs) enable automated client certificate selection, minimizing user input and facilitating administrative separation of certificates used for different environments.
RFC 3770 contained a typographical error in the OID for the Wireless LAN SSID Attribute Certificate Attribute (id-aca-wlanSSID). RFC 4334 corrects this error; implementations based on RFC 3770 may have used the wrong OID arc.
The SSID extension MAY appear in certificates that do not include the extended key usage extension, clarifying that the two extensions are independently optional.
If a certificate contains both a key usage extension and an extended key usage extension, both extensions MUST be processed independently, and the certificate MUST only be used for a purpose consistent with both extensions.
If the extended key usage extension appears in the same certificate as the SSID extension, then the extended key usage extension MUST indicate that the certified public key is appropriate for use with EAP in the LAN environment by including the id-kp-eapOverLAN KeyPurposeId value.
If there is no purpose consistent with both a key usage extension and an extended key usage extension present in the same certificate, the certificate-using application MUST NOT use the certificate for any purpose.
In cases where a human user is unavailable and automatic SSID-based certificate selection fails, each potential certificate MAY be tried until one succeeds.
The CA MUST ensure that the correct values for the extended key usage extension and SSID extension are inserted in each certificate that is issued, as incorrect representation could cause relying parties to incorrectly accept or reject certificates.
The extended key usage extension MAY, at the option of the certificate issuer, be either critical or non-critical.
When automatic certificate selection fails due to duplicate SSIDs across different WLANs, the implementation SHOULD obtain help from the user to choose the correct certificate.
The WLAN SSID attribute certificate attribute (id-aca-wlanSSID, { id-aca 7 }) associates a list of SSIDs with a public key certificate via an attribute certificate when the public key certificate does not include the WLAN SSID certificate extension. It uses the same SSIDList syntax.
The WLAN SSID public key certificate extension (id-pe-wlanSSID, { id-pe 13 }) is always non-critical and contains a list of SSIDs encoded as SSIDList ::= SEQUENCE SIZE (1..MAX) OF SSID, where SSID ::= OCTET STRING (SIZE (1..32)).
Two EAP extended key usage OID values are defined: id-kp-eapOverPPP ({ id-kp 13 }) for EAP in PPP environments and id-kp-eapOverLAN ({ id-kp 14 }) for EAP in LAN/WLAN environments. Inclusion of both indicates the certified public key is appropriate for either environment.
OIDs used in this document (id-kp-eapOverPPP, id-kp-eapOverLAN, id-pe-wlanSSID, id-aca-wlanSSID) were assigned from an arc delegated by IANA; no further IANA action is required for this document.
In practice, SSID disclosure via certificates is of little concern because other WLAN management messages already include the SSID, so masking the SSID in AP beacons only forces an attacker to eavesdrop on management messages instead. Placing the SSID in the certificate does not worsen the security posture.
When automatic certificate selection fails due to non-unique SSIDs, sequentially trying each certificate discloses the list of SSIDs associated with each certificate. It is RECOMMENDED that sequential certificate trials only be employed when user selection is unavailable or impractical.
When the same peer certificate is used to authenticate to multiple WLANs, the list of SSIDs is available from servers associated with each WLAN and is also exposed to eavesdroppers. When SSID disclosure is a concern, different peer certificates SHOULD be used for each WLAN.
The SSID field is encoded as an OCTET STRING of SIZE (1..32) bytes. The SSIDList extension value is a SEQUENCE of one or more such SSID values, using ASN.1 DER encoding per X.690.
The WLAN SSID attribute certificate attribute syntax is identical to the certificate extension: SSIDList ::= SEQUENCE SIZE (1..MAX) OF SSID, where SSID ::= OCTET STRING (SIZE (1..32)).