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Andrew Secure RPC

Author(s): M. Satyanarayanan  (1987)

Summary: Exchanged of a fresh shared key. Symmetric key cryptography.

Protocol specification (in common syntax)

A, B :   principal
Kab, K'ab :   symkey
Na, Nb, N'b :   nonce
succ :   nonce -> nonce

1.   A -> B :   A, {Na}Kab
2.   B -> A :   {succNa, Nb}Kab
3.   A -> B :   {succNb}Kab
4.   B -> A :   {K'ab, N'b}Kab

Description of the protocol rules

This protocol establishes the fresh shared symmetric key K'ab. The nonce N'b is sent in message 4 to be used in a future session.

We assume that initially, the symmetric keys Kab is known only to A and B.


The protocol must guaranty the secrecy of the new shared key K'ab: in every session, the value of K'ab must be known only by the participants playing the roles of A and B.

The protocol must guaranty the authenticity of K'ab: in every session, on reception of message 4, A must be ensured that the key K'ab in the message has been created by A in the same session.



Claimed attacks

[BAN89]. The message 4 contains nothing that A knows to be fresh. Hence, an intruder I can replay this message in another session of the protocol to convinced B to accept an old compromised key.
i.1.   A -> B :   A, {Na}Kab
i.2.   B -> A :   {succNa, Nb}Kab
i.3.   A -> B :   {succNb}Kab
i.4.   B -> A :   {K'ab, N'b}Kab
ii.1.   A -> B :   A, {Ma}Kab
ii.2.   B -> A :   {succMa, Mb}Kab
ii.3.   A -> B :   {succMb}Kab
ii.4.   B -> I(A) :   {K''ab, M'b}Kab
ii.4.   I(B) -> A :   {K'ab, N'b}Kab

See also

BAN modified Andrew Secure RPC, BAN concrete Andrew Secure RPC, Lowe modified BAN concrete Andrew Secure RPC.


Michael Burrows, Martin Abadi, and Roger Needham. A logic of authentication. Technical Report 39, Digital Systems Research Center, february 1989.

M. Satyanarayanan. Integrating security in a large distributed system. ACM Transactions on Computer Systems, 7(3):247--280, 1989.
last modified 14/11/2011.
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