# Questions tagged [known-plaintext-attack]

The attacker knows at least one sample of both the plain text and the cipher text.

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### What were Alan Turing and their team searching before doing KPA in the movie "The imitation game"?

I just watched the movie "The imitation game" (2014) which is based on Alan Turing's biography. At some point in the movie the machine built by Turing wasn't fast enough to decrypt the ...
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### KPA-Security definition

In cryptography there are 4 basic attack classifications: Ciphertext-Only Attack Known-Plaintext Attack Chosen-Plaintext Attack Chosen-Ciphertext Attack In Katz & Lindell's textbook (2nd edition)...
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### Is it allowable to put a restriction on the length of the plaintext used in the known-plaintext attack?

The definition of the known-plaintext attack: I have a plaintext and I can encrypt it to have its ciphertext, then I use this pair to break the cipher. The question: The only thing I further assume is ...
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### Number of plaintext–ciphertext pairs needed to rule out false keys with a reasonable likelihood in AES

I am new to cryptography and I've got the following question from Understanding Cryptography: Imagine that aliens — rather than abducting earthlings and performing strange experiments on them — drop a ...
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### Known Plaintext attacks using standard greetings etc

In all modern ciphers, even if one bit of input changes, then half of the output will change because of diffusion. Considering this, how exactly will knowing standard salutations, etc. ("Hello ...
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### Known Plain Text Attack DES-OFB on Crack.sh

I am trying to do a known plaintext attack on DES-OFB through crack.sh. I have been having trouble lately. I keep getting blank text file back with no keys returned. Does anybody know if DES-OFB is ...
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### Known plaintext attack on AES with CBC

Assume I have a plaintext and a ciphertext, encrypted using some key and AES with CBC mode. I don't have a service, that I can send something to, so I can't use the Padding Oracle attack. Are there ...
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### How much more secure is $c = mg_1^r + g_2(g_1(g_1^r-1)/(g_1-1)) \mod p$ compared to just $c = mg_1^r \mod p$ (dis. log), all known but $r$?

To encode a message $m$ to a cipher $c$ you can use the only hard solvable problem of computing the discrete logarithm with a generator $g$ in base over a prime $p$. $c = mg_1^r$ mod p If an ...
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### IV Re-use and Chosen Plaintext against 56bit Blowfish (CBC)

I am looking at a very old protocol which uses Blowfish to encrypt packets with a constant 8-byte IV in CBC mode. Assuming I have: The ability to arbitrary encrypt known plaintexts The IV I know ...
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### how to compute IV with AES CTR if key, plaintext and ciphertext are known?

Given $E_k$, which a block-cipher using the (known) key $k$, and a plaintext-ciphertext pair $(p,c)$ where $c$ is the encryption of $p$ using CTR mode, can the initialization vector be recovered using ...
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### Is it necessary to study the KPA security for asymmetric encryption algorithms in addition to CPA security? [duplicate]

In a KPA attack model, an adversary $\mathcal{A}$ has access to pairs of messages $(m_i,c_i)$ which are encrypted using some asymmetric algorithm. However, assuming either El-Gamal or RSA algorithms, ...
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### show that G' is not a secure PRG even if G is

Hello I'm trying to show that the function G'(s) = G(s) || G(G(s)) is not a secure PRG even if G is. My first question is that in this case, how do I know what G ...
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### AES-CBC ciphertext manipulation with known IV and plaintext! [duplicate]

I'm currently practicing on a purposely flawed login page, where I have to change the value of a cookie to enter. The cookie is an encrypted and encoded form of a simple JSON string with fields "admin"...
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### Is my deniable encryption scheme reasonable?

I was experimenting with RubberhoseFS, but since it is very hard to compile on anything modern, I decided to implement my own version, stripped of many unnecessary features. Namely, my implementation ...
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### Is it possible to find the key for AES ECB if I have a list of plaintext and corresponding ciphertext?

Assume I have a list of plaintext text and its corresponding ciphertext which was created using a specific key with AES in ECB mode. Can I recover that key? If, how big does the list of plaintext ...
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### On CPA & KPA security of $\boxplus$-Feistel

I am interested to identify the effect of replacing $\oplus$ with $\boxplus$ on basic balanced Feistel structures over $r$-rounds. Given: $F_\boxplus[L,R]= [S,T] = [R,L \boxplus f(R)]$ where $f$ is a ...
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### Known Plaintext Attack for Modified OFB Mode of Operation

Question: Assume a variant of the OFB mode by which we only feedback the 8 most significant bits of the cipher output. We use AES and fill the remaining 120 input bits to the cipher with 0's: Why is ...
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### Known Plaintext Attack on Block Cipher in ECB and CBC Modes of Operations

These 2 similar questions are from Paar's Understanding Cryptography. I could not see the answer so if someone can help I will appreciate: Question1: We consider known plaintext attacks on block ...
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### Ethereum RLPx protocol for inter-node communication - flaws in the encryption

Ethereum uses RLPx/devp2p for inter-node communication. The protocol is encrypted using Elliptic Curve Integrated Encryption Scheme (see ref) Under Known-Issues I found this paragraph: The RLPx ...
Consider a simple, 1-round Feistel network. Because the ciphertext is essentially $(L_1,R_1)$, if one knows the plaintext $(L_0,R_0)$, the only unknown left is $K$. However round functions in ...