RADIUS attribute from rfc2869

---

ARAP-Security-Data

This attribute contains the actual security module challenge or
      response, and can be found in Access-Challenge and Access-Request
      packets.

   A summary of the ARAP-Security-Data attribute format is shown below.
   The fields are transmitted from left to right.

    0                   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      |    Length     |     String...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      74 for ARAP-Security-Data.

   Length

      >=3

   String

      The String field contains the security module challenge or
      response associated with the ARAP Security Module specified in
      ARAP-Security.

---