Linked Questions

8
votes
1answer
1k views

What is a related key?

We talk of related keys and related key attacks, but what is a 'related key'? So in three related parts:- How can one key be related to another key? Is there a metric describing the degree of ...
7
votes
2answers
1k views

What is the importance of Rcon in Rjindael's key expansion from a security prespective?

I do not see why the Rcon function is important, it looks like a waste of cycles. $$\operatorname{Rcon}(i) = 2^{i-1} \bmod p(x)$$ is in $\operatorname{GF}(2^8)$, ...
6
votes
2answers
389 views

Do test vectors ensure a cipher is free of backdoors?

If a cipher implementation passes unit tests using test vectors from some trusted source (these for AES, for example), then can we say that it is fully conforming to the specification, and must have ...
4
votes
2answers
1k views

Can a 1 byte difference in AES 128 bit keys make huge difference in output?

If we take some randomly generated key of AES-128 and we change any random 1 byte of that 16 byte key, will this make huge difference in the AES cipher text generated over same input string? Does ...
6
votes
1answer
1k views

Choice between AES-128 and AES-256 for password protection in MS Office

Why are we still using the default of AES-128 when password protecting a Microsoft Word document. My answer is and always has been - because its good enough and MS don't recommend changing to AES-256. ...
3
votes
2answers
856 views

Security of AES in CTR mode with fixed nonce (but different key)

If I am using AES in CTR mode and use a unique key every time but the same nonce, is this secure? If so, does it make a difference if the nonce is public?
5
votes
3answers
775 views

Post Quantum Symmetric Cryptography

So I am looking for the most secure method of symmetric key cryptography for long term messaging use between two users. I have heard that most symmetric key algorithms are not absolutely compromised ...
1
vote
2answers
461 views

How do Hash functions work under the hood? [closed]

Using and benefiting from hash functions on a daily basis, I keep wondering how hash functions actually work down in their core. Most of the available resources I found, only explained hash functions ...
1
vote
1answer
2k views

How often do I need to rotate AES 256 keys

I'm trying to design a protocol for a resource constrained environment. The device has to communicate with a server through an insecure node. My plan is to use AES 256 end to end for all ...
3
votes
2answers
1k views

Consider the use of double encryption applied to the AES algorithm with two 128-bit keys

Actual Question below. Consider the use of double encryption applied to the AES algorithm with two 128-bit keys. How much storage and computation would be required to execute a meet-in-the-middle ...
0
votes
1answer
83 views

Is a new block cipher harder to design than a new hash?

I realise that cipher and hash primitives are somewhat different. But they share common requirements like attack resistance amongst others. And I realise that attacks /vulnerabilities are ...
2
votes
1answer
125 views

Are two keys derived from the same password vulnerable to a related key attack?

Background I am currently writing a password manager application. As usual, the passwords are put in a file encrypted using a user-entered password. I'm using the NaCl library but actually it's not ...