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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2answers
270 views

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 ...
7
votes
1answer
136 views

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 ...
7
votes
3answers
217 views

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 ...
2
votes
1answer
67 views

IKEv2: Why is it important “that each side sign the other side's nonce”

I am currently diging deep into the IKEv2 protocol. In the description of the Authentication (RFC5996, p. 48), the following statement is given: "It is critical to the security of the exchange that ...
1
vote
3answers
53 views

Secure Custom Registration Links

I'm working on a website that allows a current user to invite another individual to be friends by typing in the non-user's email address. The non-user would then receive a custom registration url by ...
1
vote
1answer
119 views

Is this where a nonce comes into play?

I'm reviewing a website a friend developed, and was looking for general errors and concerns. In reviewing I noticed he is very heavy on ajax calls using JSON to a RESTful API that he maintains on a ...
1
vote
2answers
221 views

Is it safe to use Diffie-Hellman public keys as nonces to protect against replay attacks?

I have an interesting case regarding protection against replay attacks. Under the assumption that Alice and Bob have used Diffie-Hellman key exchange to establish a secure temporary session, would it ...
0
votes
1answer
115 views

How to use a token to differentiate between a valid logged in user and an attack?

Let us take the example of my already being logged in to, say, LinkedIn. When I access LinkedIn on a new tab, it automatically logs me in (using cookie info). Now, suppose I visit a forum and through ...
0
votes
1answer
156 views

Is it insecure to ask for the current nonce from server?

I'm developing an embedded application that delivers information through HTTP to my web server. These deliveries are secured by a hash H(secret : data : nonce) where the secret is shared between ...
3
votes
3answers
821 views

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 ...
6
votes
1answer
226 views

Encrypting short identifiers?

I am developing a webapp that does not reveal record count, because it hides the primary key. I am looking for a better way to do this. My favorite idea is to encrypt the ID itself with a block ...
6
votes
1answer
596 views

Prevent cross domain form submission with nonce?

I haven't done much in web security before but am now in need to prevent a form from being submitted from anything but my own domain. I know how to lock this down in an .htaccess file but the ...
3
votes
1answer
322 views

Are man-in-the-middle attacks against p2p systems realistic?

I'm implementing a DHT based on Kademlia following this paper. The protocol described in this paper uses nonces to protect against man-in-the-middle attacks. The disadvantage is that latency gets ...
5
votes
2answers
1k views

Do Client Nonces enhance the security of HTTP Digest Auth?

As far as I understand the answer at http://security.stackexchange.com/a/3024/13447, client nonces are meant to prevent attackers from amortizing the costs of brute-force hash computations by being ...
8
votes
2answers
3k views

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 ...
4
votes
3answers
2k views

optimal way to salt password?

A good way to salt password? I have read a few answers related to salting password. But I started to get confused. I came across few functions people used to generate salt like: mcrypt_create_iv() ...
9
votes
1answer
3k views

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? ...
7
votes
1answer
1k views

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 ...
1
vote
3answers
589 views

Three Message Authentication Protocol

I have a protocol where "A" initiates communication with "B". "B" then sends a challenge to check if "A" is really "A". "B" does not remember sending the challenge so "A" has to respond by sending the ...
6
votes
3answers
889 views

chosen plaintext attacks against MD5 and SHA1

According to http://tools.ietf.org/html/rfc2617#section-4.9, having the server chose a nonce but not having the client chose a nonce opens up Digest Access authentication to chosen plaintext attacks. ...
1
vote
1answer
592 views

Nonce construction for CTR mode (Mcrypt)

Edit: I'll put up this more clearly. By the most simplest form, I'm asking that if I AES encrypt in CTR more with Mcrypt (using PHP), can I create the "IV" by just simply reading 16 bytes from ...
9
votes
1answer
3k views

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 ...
39
votes
4answers
12k views

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 ...
9
votes
1answer
2k views

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 ...
17
votes
3answers
4k views

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 ...