IT Security Stack Exchange
IT Security Stack Exchange

Questions tagged [nonce]

a random number that is only used once. It is generated at the beginning of a communication by one communication partner and has to be sent back by the other one in order to prevent replay attacks.

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What is the use of a client nonce?

After reading Part I of Ross Anderson's book, Security Engineering, and clarifying some topics on Wikipedia, I came across the idea of Client Nonce (cnonce). Ross never mentions it in his book and I'm struggling to understand the purpose it serves…
user2014
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When using AES and CBC, is it necessary to keep the IV secret?

If I encrypt some data with a randomly generated Key and Initialization Vector, then store all three pieces of information in the same table row; is it necessary to encrypt the IV as well as the Key? Simplified table structure: Encrypted data Key…
Stu Pegg
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How long should a random nonce be?

NIST provides good guidelines on the length of keys and hashes for various algorithms. But I don't see anything specifically on the length of a random or pseudo-random nonce (number used once). If there is a single good answer for a variety of…
nealmcb
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How does a nonce reset allow for decryption?

I'm sure that by now most InfoSec-lovers have heard about KRACK. If you haven't, check out this great explaination by a fellow StackExchanger. It's a new attack on WPA2 which allows for decryption and forging of packets in certain (and certainly…
FMaz
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Why does the SSL/TLS handshake have a client and server random?

In the SSL handshake both the client and server generate their respective random numbers. The client then generates a pre master secret and encrypts it with the server's public key. However, why can't the client just generate the pre master secret…
George Robinson
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Openid connect nonce replay attack

The openid connect specification adds a nonce parameter to the authorize endpoint, which must be echoed back as a claim in the id_token. It claims that the purpose of this parameter is to prevent replay attacks and has some implementation…
user3072507
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Purpose of nonce validation in OpenID Connect implicit flow

The OpenID Connect specification requires implicit flow clients to generate and validate a nonce: String value used to associate a Client session with an ID Token, and to mitigate replay attacks. What replay attacks are those? Put differently,…
meriton
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when to use nonce?

I have trouble understanding nonce. I read a very good answer related to nonce by @Thomas Pornin, but it is too complicated for me as I am new to cryptography. From what I know, nonce is used to validate a form upon submission and avoid resubmission…
Loonb
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SSL replay attack when client/server random is missing

Hey studying the SSL protocol, I'm wondering how can someone be able to do a replay attack if the server nonce is missing? All the material I find says that nonces prevent it, but theres no examples which specify why or how
ddayan
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TLS replay attack - requirements of the serverHello nonce

As you all know, the SSL/TLS protocol requires both client and server to exchange (in clear text) a random number or nonce. This is presumably used to prevent replay attacks. It is not clear to me what the server-side nonce requirement is. Must it…
Louis
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Is it possible to implement a nonce without storage?

I am looking at implementing an authentication module using OAuth 2.0 Client and I am trying to avoid having any server state. I was going thorough a few other questions when to use nonce? Is it possible to have stateless server nonces in HTTP…
Archimedes Trajano
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What's the point of the nonce in CTR mode?

Does having a nonce in CTR mode actually improve security (vs. just using 1, 2, 3, etc. - basically a constant nonce of 0)? As far as I can tell, the best-case scenario security-wise is that the nonce could act as a sort of second key, which would…
Neil Fitzgerald
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According to RFC 5246, are nonces in TLS useless (in terms of security) and if yes, why aren't they only random data?

I know the common usage of nonces in security (which is well described in this topic). However, when checking the SSL/TLS protocol, we can notice, according to the RFC, that nonces as ClientHello.random and ServerHello.random are sent in plaintext…
blingbou
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Is it possible to have stateless server nonces in HTTP Digest

When implementing a HTTP Digest server, there's the issue of nonces. Server nonces (as opposed to client nonces) must be issued by the server may be re-used by clients as long as the server allows it knows nothing about what user will use the nonce…
mogsie
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How can salted, hashed password storage be combined with a plaintext, nonce and hash based authentication?

My understanding is as follows: To securely store a password (e.g. in a database), you use a hashing algorithm designed for this purpose (designed to be slow, e.g. bcrypt), and you use a unique salt for each password. This makes it hard/slow for…
Tim
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