Linked Questions

0 votes
0 answers

AES-CTR key reuse attack with same IV and known plain text [duplicate]

this is from an IT Security exercise which my friend and me cannot solve. Given 2 AES-CTR stream-cipher encrypted files Same known initalizing vector Same (unkown) key Same 128bit Counter ...
Elias's user avatar
  • 1
120 votes
7 answers

Taking advantage of one-time pad key reuse?

Suppose Alice wants to send encryptions (under a one-time pad) of $m_1$ and $m_2$ to Bob over a public channel. Alice and Bob have a shared key $k$; however, both messages are the same length as the ...
Elliott's user avatar
  • 1,661
76 votes
3 answers

How does one attack a two-time pad (i.e. one time pad with key reuse)?

My question might appear the same as the question Taking advantage of one-time pad key reuse?, but actually I did read all the answers and none of them helped me with the details I need. I am new to ...
Samer Makary's user avatar
11 votes
5 answers

What is the purely mathematical definition of encryption strength?

An encryption function can be used to obfuscate pieces of information and later on retrieve them. What is the yardstick for measuring how well the function encrypts the information ? Given any ...
ARi's user avatar
  • 235
14 votes
1 answer

Reusing keys with AES-CBC

I heard that key/IV pairs must not be reused in AES-CTR, or when using any stream cipher for that matter. Yet the attacks described do not seem to apply to AES-CBC. Is reusing the same key several ...
user2398029's user avatar
2 votes
2 answers

AES-256 GCM IV guidelines

If I use for example AES-256 (GCM), and my message is bigger than 256 bit (broken into smaller 256 bit blocks for encryption), should the IV change for every 256 bits of the message?
Offir's user avatar
  • 283
4 votes
3 answers

"Weak" implementation of AES-CTR?

Assume an instantiation of AES-CTR like in the following picture: Some details on the input-values for keystream generation: COUNT: a 32-bit value associated with ...
Jimakos's user avatar
  • 705
2 votes
1 answer

AES 128 bits with 12 bytes IV vector composed of a 4 bytes counter : safe?

I have a 128 bits AES cypher (GCM, Galois/Counter Mode) using a 12-byte initialization vector (IV) composed of: 8 constant bytes: 6 bytes (device ID) 2 bytes (zero) 4 bytes (incrementing frame ...
Laurent Grégoire's user avatar
1 vote
2 answers

(Re-)Using deterministic IV in CTR mode / How to: deterministic AES

I am aware of the requirement of an IV to be unique in CTR mode (Why must IV/key-pairs not be reused in CTR mode?). However I wonder if I can use an IV depending on the plaintext deterministically. ...
Sebastian S's user avatar
1 vote
2 answers

Scrypt KDF cipher (scrypt CLI) - known vulnerabilities and cryptanalysis?

There is a scrypt cipher that is used for example by some cryptos like LItecoin for their mining algorithm. I never heard of scrypt. I know eg SHA-256 which is well analyzed and considered as secure ...
johnsmiththelird's user avatar
2 votes
1 answer

Is predictable ciphertext/plaintext bad?

I have a cryptosystem that I'm using for secure chat. It is using AES 256 (with RSA 2048 for key exchange). Would a predictable, and repetitively sent ciphertext plaintext compromise the ...
kys111's user avatar
  • 21
2 votes
2 answers

How much data do I leak if I use the first bytes of a file as AES-CBC IV?

I found a piece of code that uses the first 16 bytes of the input file as IV. This immediately set off some flags in my head, but I have no idea how bad it really is. So, how bad is it? Obviously we'...
Filip Haglund's user avatar
5 votes
0 answers

How can I find two strings $m_1$ and $m_2$, knowing that I know $m_1 \oplus m_2$? [duplicate]

Possible Duplicate: How does one attack a two-time pad (i.e. one time pad with key reuse)? I recently started to follow the cryptography class of Dan Boneh on and the first part is ...
SRKX's user avatar
  • 151
1 vote
2 answers

Encrypting/Decrypting sensitive information for storage purpose

I want to store account numbers and routing numbers into SQL database, and i was looking for best way to encrypt/decrypt this sensitive information. After researching i found i can use symmetric (like ...
LP13's user avatar
  • 111
1 vote
1 answer

Can I use different IVs when encrypting identical plaintexts with identical keys with AES-CTR?

I would like to use AES-CTR to encrypt the same plaintext with the same key more than once (on different machines). I'm wondering whether I should try to use the same IV each time, or whether it's ...
Daniel Brauer's user avatar

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