Linked Questions

7
votes
1answer
274 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 ...
4
votes
1answer
681 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 ...
4
votes
1answer
5k 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 ...
3
votes
1answer
114 views

Best practices for IV generation

What are the best practices for IV generation for AES and other algorithms? Is RNG enough? What if I cannot use RNG and need to use a variable that is related to some characteristic of the ...
3
votes
1answer
166 views

BEAST Attack: from guessing to decoding

I understood the XOR trick that allows an attacker to guess a block of a previously sent message from the client to the server: the attacker forces the client to send the message $\tilde{m} = c_n \...
2
votes
1answer
273 views

Attack on AES-CBC with small pool of IV

Let's assume that for encryption with AES in CBC mode we have $IV\in \{0\}^{113}||\{0,1\}^{15}$. I know that if we can predict next IV with 100% probability there is attack that completely breaks ...
2
votes
1answer
646 views

Plaintext block chaining, bad idea why?

Ahead of the question, little warning. Question is not about what are the better options. Question is why it is bad idea? Ok, suppose we have plaintext $p$, which divided into blocks: $p_1,p_2,p_3,......
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 ...
1
vote
1answer
406 views

Is it safe to send IV in plain text for every request?

Currently, I am creating a project with an IoT device. This is an offline device which shows a QR code which can be scanned by a mobile device, which sends this code to a server. The server handles ...
1
vote
1answer
567 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 ...
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 ...
1
vote
1answer
77 views

Initialization vector based on data which can be changed by an attacker

We need to exchange some data encrypted between a device and our software where the device does not have access to a source of randomness. Both the software and the device know the key (although they ...
0
votes
1answer
50 views

Randomly initialised global counter used to encrypt the kth message with IV = IV + k mod 2^n

The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then IV + 1 for the second , IV + 2 for the 3rd etc. How can I construct an attack to ...
-4
votes
1answer
183 views

at rest encrypton question from someone who knows nothing

this forum is way above me and the members here are far, far smarter than I am, so this probaby isn't the place to ask such a simple question, but whatever. All I wanted to ask is for at rest ...
1
vote
0answers
91 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 ...

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