# Tagged Questions

Needham–Schroeder refers to both, a symmetric key or a public key authentication protocol.

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### When would you increment a nonce and when not?

K is the shared key for encryption known by _Alice and _Bob. $N_A$ is a nonce created by Alice. The function f is the increment by 1 function. (1) Alice -> Bob: $E_K(N_A)$ So Alice encrypts a nonce ...
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### In Needham Schroeder key distribution what happens if responder's part is not encrypted in step 2 with Kbs but encrypted instead by Kab in step 3

The Needham-Schroeder protocol is: 1 A→S:A,B,Na 2 S→A:{Na,B,Kab,{Kab,A}Kbs}Kas 3 A→B:{Kab,A}Kbs 4 B→A:{Nb}Kab 5 A→B:{Nb−1}Kab Here Na and Nb are nonces. Kab is the key between a and b Kas is ...
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### Insecurity in Needham and Schroeder protocol?

I've been studying specifically the authentication algorithm Needham and Shroeder, and understand the idea in general of the message exchange. But, researching on the subject, I found a question that ...
Here is the protocol outline I am looking at (source: Foundations of Computer Security, Lecture 60: The Needham-Schroeder Protocol)  \begin{array}{ccl} 1.& A \to S \colon& A,B,N_a \\ ...