Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [challenge-response]

Challenge-response authentication is a family of protocols in which one party presents a question ("challenge") and another party must provide a valid answer ("response") to be authenticated.

1
vote
2answers
42 views

Zero Knowledge for Low Entropy Witness

For any PPT prover ($p$) and verifier ($v$), imagine I have a low entropy witness, say smaller than $2^8$. Now, let us say I have a dlog statement in the form of $y = g^w$. Theory says I could use a ...
0
votes
1answer
60 views

How to compute a challenge c using Fiat Shamir?

I have a prover and verifier. They are engaged in a zero-knowledge proof protocol. A verifier sends a challenge $c$ to the prover so he can compute a proof using the value $c$. How to use Fiat Shamir ...
7
votes
1answer
273 views

What is the use of SCRAM-SHA-256 (over SCRAM-SHA-1)?

The Salted Challenge Response Authentication Mechanism (SCRAM) specified in RFC 5802 can use arbitrary hash functions to operate. The base version from RFC 5802 uses SHA-1. From my understanding, ...
2
votes
1answer
82 views

Challenge - Response protocol - how to incorporate client randomness

I am designing a challenge-response protocol to enable a client to authenticate to a server. The client has a private key, and a certificate (issued by a trusted CA). At this point in the protocol, ...
1
vote
0answers
64 views

PKI Challenge Response: why is $h(r) = x$ enough to protect against chosen text attacks?

I think the question was asked somewhere else but not answered very precisely. Quoting from the "Handbook of applied cryptography": Identification based on PK decryption and witness. Consider ...
1
vote
1answer
212 views

regarding nonce and secret key

Consider the following challenge-response protocol for $A$ to convince $B$ that he is indeed $A$. Here we are assuming: at the start when the virtual circuit is being set up, $A$ has to convince $B$ ...
3
votes
1answer
287 views

Diffie-Hellman based password challenge response scheme

A very commonly used (examples: HTTP digest auth/CHAP/Kerberos) authentication scheme is something that looks like: Setup. Client and server both know a password $p$. Authentication. Server sends ...
0
votes
1answer
99 views

Why are they called “commitment”, “challenge”, and “response”?

I'm reading Proof Systems for General Statements about Discrete Logarithms, and I think I'll have a better understanding of the process if I can understand where the terms come from. They give a basic ...
1
vote
1answer
307 views

Challenge Response at Application Layer of BLE using ECDSA

There is a need for an Offline BLE device to Auth a Phone. I am planning to use challenge response somewhat outlined here. There is a small change. Instead of shared secret. I am planning to use a ...
3
votes
1answer
157 views

Challenge to prove possession of file

Suppose Bob wants to give Alice a large file, in such a way that: Bob cannot keep the file, but is able to use it to precompute anything he needs before he gives it to Alice Bob must be able to ...
2
votes
2answers
773 views

Challenge Response Authentication - Client Generating Challenge

Let's say we have a client (the not trusted party) and the server(wants to verify that the client is who he claims to be. The <...
1
vote
0answers
93 views

WEP: Why is the challenge string randomized?

In WEP, the 128-bit challenge string generated by an access point would allow for approximately 340 undecillion unique strings. Would it be problematic were a string to be reused? I suppose with $2^{...
1
vote
1answer
300 views

Appropriate length of the challenge string for challenge-response authentication?

How to select the necessary length of the challenge string for challenge-response authentication to claim that there is no threat of the shared secret exposure? I can think of the following: ...
7
votes
1answer
493 views

Commutative Hash Function for Password Challenge?

I had an idea. Could anyone tell me if this is a thing, if they see any problems with it, and if they know of a commutative hash function that would make it work? Suppose you had a pair of ...
3
votes
1answer
419 views

Reuse of TLS client key/certificate in challenge-response protocol

The situation: We have a custom PKI with clients communicating with the server over standard SSL/TLS encrypted channel. PKI uses ECC, server certificate supports ECDHE_ECDSA key exchange mechanism and ...
4
votes
1answer
3k views

Client Puzzles and HMAC

I'm learning about client puzzles for DoS (Denial of Services) Protection, and I came across this question. For each request, the server sends the client a freshly generated random challenge r and ...
3
votes
1answer
792 views

Is this DIY remote lock protocol secure?

I need your advice on following scheme of exchange protocol between remote lock and key. I'm planning to use following algorithm: Key generates unique value that never repeats (in reality it's just ...
1
vote
1answer
163 views

Proof of Knowledge/Data Integrity using Hash Function

Objective: A verifier wants to ensure that a block of data M is also known to a prover. The protocol should exchange little information and should not leak information about the value of M. Proposed ...
2
votes
0answers
410 views

StoredKey in Salted Challenge Response Mechanism (SCRAM)

In SCRAM (RFC5802, page 8) the client generates ClientKey to server, which is a derivation of the original password. This is communicated to the server in a secure ...
5
votes
2answers
818 views

Is there a difference between asking for a signature and asking for a decryption in challenge-response authentication?

Consider the following two authentication schemes. In both cases the server knows a public key of the client (for a signature system in the first and an encryption system in the second case). Scheme ...
3
votes
1answer
140 views

Proof that two parties can communicate

Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if ...
3
votes
1answer
355 views

Is there a scheme that allows to use RSA based challenge response protocol limited to signing only 8 bytes to create a secure signature of any data?

I have a tiny device that has a challenge-response authentication mechanism where the device signs 8 bytes of any data with it's internal 2048 bit RSA key. I would like to be able to certify any data ...
0
votes
1answer
366 views

Why should I use X.509 Authentication over PKC based Authentication?

So I have two examples and I don't understand why one would be chosen over the other. Example 1. A sends EPUb[r1] to B (asks B to prove knowledge of ...
2
votes
1answer
211 views

Can adding nonces make challenge response authentications weaker?

In a custom protocol we want to replace an aged tiger32 based challenge response authentication. I suggested that we use something existing, so threw HMAC into the room. As per wikipedia it works as: ...
2
votes
0answers
2k views

Challenge-response based on public-key decryption, why send public key

Quoting the handbook of applied cryptography, chapter 10.3.3 (i): Identification based on PK decryption and witness. Consider the following protocol: $A \leftarrow B: h(r), B, P_A(r,B)$ $...
4
votes
2answers
496 views

Spoofing protocol nonce

Amy and Betty have a shared key $k$, and the protocol below is to provide a mutual authentication for both Betty and Amy. A sends B : $n_a$ B sends A : $n_b \;\|\; E(k, n_a)$ A sends B : $E(k, n_b)$ ...
1
vote
0answers
176 views

Challenge–response authentication which can be done in head?

Say we have door where you have to say a password to pass. If theres someone standing nearby he would hear the password and could also use it. So therefore the doorman gives you a different number ...
1
vote
1answer
173 views

Why send a challenge with CHAP?

I have been reading about the Challenge-Handshake authentication Protocol (aka CHAP). Why send a challenge to the user and ask them to hash that challenge with the symmetric key and send that hash ...
2
votes
2answers
641 views

Help me describe/identify this challenge-response protocol/algorithm?

My area of expertise is reverse engineering, specifically embedded systems. I do attack cryptographic systems, but this largely involves key recovery or exploiting the implementation. I was asked to ...
3
votes
2answers
542 views

Zero-Knowledge Challenge-Responce Protocol

Good day to everyone. I am trying to implement an e voting system (just for reference -it is not important though-it is described at the Internet Voting Protocol Based on Improved Implicit Security ...
5
votes
2answers
830 views

What challenge should I use in a challenge-response proof-of-work?

In order to guard against denial-of-service attacks, I want to require clients to do some work (more work than the server does fulfilling the request) before talking to them. Client connects Server ...
1
vote
1answer
175 views

How is the password sent across for verification?

I am familiar with Challenge-Response Authentication scheme. However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel. ...
2
votes
1answer
2k views

Hash or encryption function for challenge-response protocol?

Say I have an authentication protocol where the shared secret is never transmitted. The server passes a challenge to the client and the client calculates a response using an algorithm where the ...