Linked Questions

0
votes
2answers
84 views

Randomly initialised global counter used to encrypt the kth message with $\operatorname{IV} = \operatorname{IV} + k \hspace{5mm} mod \hspace{5mm} 2^n$ [duplicate]

The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then $\operatorname{IV} + 1$ for the second , $\operatorname{IV}+ 2$ for the 3rd etc. How ...
1
vote
0answers
93 views

AES CBC Initialization vector - Security issues [duplicate]

I have 2 questions regarding security issues related to initialization vectors used in AES CBC Consider that I'm using a sequence number (which increments with every encryption) as an initialization ...
79
votes
9answers
115k views

Should I use ECB or CBC encryption mode for my block cipher?

Can someone tell me which mode out of ECB and CBC is better, and how to decide which mode to use? Are there any other modes which are better?
31
votes
2answers
7k views

7zip : Why does encrypting the same file with AES-256 not give the same output?

Using 7-zip 19.00, on Windows 10 1909, build 18363.592, I encrypted a text file with the contents "hello there" using AES-256 and the password "123". I did this two times, the exact same procedure, ...
21
votes
3answers
33k views

How can Cipher Block Chaining (CBC) in SSL be attacked?

I am trying to understand how CBC-mode in SSL/TLS can be attacked. I have been looking around online but all examples and explanations are very hard to understand and follow. Can you give a simple ...
10
votes
1answer
1k views

Which block cipher parameters should be kept secret?

Which of the parameters of a block cipher (e.g., algorithm name, mode of operation, IV (if any), key length) are essential to keep secret?
4
votes
1answer
6k views

CBC with a fixed or random IV

I have three questions related to the use of IV within CBC mode of operation: Why, exactly, is it so bad to have a fixed (or predictable) IV in CBC mode? An example would be great! Given 1., why is a ...
8
votes
2answers
1k views

CBC variant: why encrypt the nonce with a different key?

I am a newbie at cryptography. I understand the CBC encryption, somewhat. You don't want to use the same "IV" for every message because then the ciphers are not very random. My question is regarding ...
7
votes
1answer
281 views

Predictable, but private IV in CBC

It is said that a predictable IV is dangerous, because you can do adaptive chosen plaintext attacks. But if the IV is never seen to the attacker, is it still dangerous? What I mean, is that the IV is ...
2
votes
1answer
1k views

Is it safe to AES-CBC and AES-CMAC both using the same key?

There is a very similar question (Using a derived key for CMAC) but it doesn't quite answer this one (at least for me it does not). I have a situation where I need to transfer some data. My data has ...
3
votes
2answers
1k views

How to defend AES against chosen-plaintext attack?

I have a server which encrypts files with the same AES key. Users can upload a file and download its encrypted version. A user can upload as many files as he wants. Users can decrypt the documents via ...
1
vote
1answer
1k views

Question about IV/initialization vectors

I found some code to get crypto-js to encrypt data in the browser, and with a pointer from someone on SO, it now decodes data as well. My next question is about the use of an IV; is an IV like a salt ...
2
votes
2answers
385 views

using different IV and SALT with AES-CBC but same KEY

I'm working on this project where a client can send a message, now obviously sending it in plainText is not very smart. So I decided to Encrypt it with AES-CBC. Now, each time I encrypt something, ...
4
votes
1answer
712 views

Fixed-prefix IV in CBC mode

I know the Initialization Vector needs to be unpredictable. Does it apply to the IV as a whole, or to every bit in the IV? I have multiple devices with poor entropy sharing the same key and I want to ...
1
vote
1answer
776 views

Simulation of Chosen Plaintext Attack on CBC, Predictable IV with OpenSSL

I would like to simulate the CBC IV attack where the IV is predictable. It's described in the answer to this question: chosen plaintext attack on CBC, predictable iv (Only "Yes" and "No" are valid ...

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