RADIUS attribute from rfc5904
The PKM-SS-Cert Attribute is variable length and MAY be transmitted in the Access-Request message. The Value field is of type string and contains the X.509 certificate binding a public key to the identifier of the Subscriber Station. The minimum size of an SS certificate exceeds the maximum size of a RADIUS attribute. Therefore, the client MUST encapsulate the certificate in the Value fields of two or more instances of the PKM-SS-Cert Attribute, each (except possibly the last) having a length of 255 octets. These multiple PKM-SS-Cert Attributes MUST appear consecutively and in order within the packet. Upon receipt, the RADIUS server MUST recover the original certificate by concatenating the Value fields of the received PKM-SS-Cert Attributes in order. A summary of the PKM-SS-Cert Attribute format is shown below. The fields are transmitted from left to right. 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Len | Value... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 137 for PKM-SS-Cert Len > 2 Value The Value field is variable length and contains a (possibly complete) portion of an X.509 certificate.