Default encryption on cisco router for radius authentication

[sarahr202]

Hi everybody

Please consider the following config: 

What encryption will R1 use while communicating with radius server?

Much appreciated!!

R1(config)# aaa new-model
R1(config)# radius-server host 192.168.2.5 auth-port 1645 acct-port 1646
R1(config)# radius-server key MyRadiusKey

[Karsten Iwen]

There is no general encryption in RADIUS. The key is mainly used for authentication and encryption of only the user-password. This is from the RFC:

      Transactions between the client and RADIUS server are
      authenticated through the use of a shared secret, which is never
      sent over the network.  In addition, any user passwords are sent
      encrypted between the client and RADIUS server, to eliminate the
      possibility that someone snooping on an unsecure network could
      determine a user's password.

[sarahr202]

Thanks Karsten,for the response.

In my example R1 is a Cisco router. When it sends radius-access request to Server, it first encrypts the message. My question is what kind of encryption R1 uses if none is specified( does it use MD5 or SHA etc)

[Karsten Iwen]

Its not the whole message that gets encrypted. The user-password is encrypted in a way that is explained in section 5.2 of the RFC:

5.2.  User-Password

   Description

      This Attribute indicates the password of the user to be
      authenticated, or the user's input following an Access-Challenge.
      It is only used in Access-Request packets.

      On transmission, the password is hidden.  The password is first
      padded at the end with nulls to a multiple of 16 octets.  A one-
      way MD5 hash is calculated over a stream of octets consisting of
      the shared secret followed by the Request Authenticator.  This
      value is XORed with the first 16 octet segment of the password and
      placed in the first 16 octets of the String field of the User-
      Password Attribute.

      If the password is longer than 16 characters, a second one-way MD5
      hash is calculated over a stream of octets consisting of the
      shared secret followed by the result of the first xor.  That hash
      is XORed with the second 16 octet segment of the password and
      placed in the second 16 octets of the String field of the User-
      Password Attribute.

      If necessary, this operation is repeated, with each xor result
      being used along with the shared secret to generate the next hash
      to xor the next segment of the password, to no more than 128
      characters.