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Questions tagged [block-cipher]

A block cipher is an encryption algorithm which encrypts fixed-size blocks of plaintext to same-sized blocks of ciphertext. For good ciphers every bit of the ciphertext block depends on every bit of the plaintext block and every bit of the key.

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How many additions modulo $2^k$ and multiplications in $\mathbb F_{2^k}$ are needed to resist cryptanalysis?

Consider a $k$-bit block cipher with $r$ rounds, and key composed of $r$ subkeys $K_i\in\{0,1\}^k-\{0^k\}$ (that is, non-zero $k$-bit bitstrings), for $i\in[0,r)$. Plaintext is $P=S_0\in\{0,1\}^k$, ...
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Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is A Statistical Saturation Attack against the Block Cipher ...
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Resistance to integral attacks by North Korean block cipher Jipsam1

The cipher is a modification to AES and is described on this website: The only difference between Jipsam1 and AES-256 is the S-box. Whereas in AES the S-box is public and constant, namely $$ \begin{...
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Why Block Ciphers

I​ fail to understand what block ciphers can do that stream ciphers cannot. Also aren't they construct able from one another. prg(stream cipher) -> prf -> prp(block cipher) Any practical example ...
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Aside from Keccak, are there any keyed/unkeyed permutations where the choice of all rotation constants is not based on heuristic methods?

I am interested to see examples of cryptographic algorithms (namely, keyed or unkeyed permutations that transform an $n$-bit input to an $n$-bit output) where the choice of all rotation values is not ...
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Safely using ciphers that take small key sizes

Is it feasible to use triple encryption for block ciphers with the maximum keysize being the only significant security issue? I mean $C = E_{k_1}(E_{k_2}(E_{k_3}(P)))$ and $P = D_{k_1}(D_{k_2}(D_{k_3}(...
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Differential Path Search of a Block Cipher

Camellia Design and Analysis document refers to a paper: [24] M. Matsui, "Differential Path Search of the Block Cipher E2," (in Japanese), Technical report of IE- ICE, ISEC99-19, pp.57-64, The ...
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How secure is $\operatorname{AES256}_{\operatorname{ECB}}(\operatorname{ChaCha20}(\text{plaintext}))$?

Suppose I encrypt a bytestream using ChaCha20, and then encrypt the resulting ciphertext using AES in ECB mode. How secure is the combination?
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A 5-bit S-Box whose differential branch number is equal to 4 and the linear branch number is not less than 3

The last paragraph of Section 1 (Introduction) of the paper “On the Relationship between Resilient Boolean Functions and Linear Branch Number of S-boxes” [S. Sarkar, K. Mandal, D. Saha] contains the ...
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Markov ciphers - generalized group operation

I’m reading this paper of Lai and Massey where they give a very nice perspective on differential attacks in general http://www.isiweb.ee.ethz.ch/papers/arch/xlai-mass-inspec-1991-3.pdf They do their ...
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How to decide which diffusion scheme is better for a block cipher design

There are several schemes that can be used to achieve the diffusion property in a block cipher. Schemes include MDS code, Bit permutation, Byte/ Nibble permutation, Diffusion Matrix, Diffusion ...
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Why are cyclic keys in Feistel Networks insecure?

So everyone seems to agree that recurring round keys in a Feistel network (eg. using the same key for every round) are a massive security leak. When researching this, the only thing I found is the ...
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Cracking a key using a combination of partial keys

As part of a cryptanalytic attack I've carried out, I used a divide-and-conquer strategy to divide the secret key $k$ into several equal-sized partial keys $k = {k_1, k_2, ...}$. The attack works ...
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mCrypton - does anyone know where I can find test vectors or a reference implementation?

I am currently writing an implementation of the mCrypton lightweight block cipher (as presented in this paper). Unfortunately, the authors do not provide any test vectors. I tried to contact the ...
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Implement Twofish cipher with 16-bit blocksize?

I've seen implementation of Rijndael cipher with 16-bit blocksize. And I have also tried to implement 16-bit Rijndael cipher by myself with only a little sneak peeking at the example of the ...
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Breaking linear blockcipher - expanding recursive formula

I am trying to break a block cipher that can be defined as follows: We have 12 rounds and at each round, we perform the following operation. We split 64 bit data into 2 parts each 32-bits, $\ x_r$ and ...
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Are there key collisions in AES-192, AES-256?

Suppose we have a single, fixed plaintext block $p$ of 128 bits. Call the set of all possible 128 bit blocks $B$. We could define fixed plaintext AES-128 as a function $f(k) \to B$ that takes a 128 ...
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Can a differential attack on FEAL4 yield multiple valid keys?

For my version of this attack I used the FEAL4 version depicted here http://theamazingking.com/crypto-feal.php and in the book "Applied Cryptanalysis Breaking Ciphers in the Real World -- Mark ...
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Design criteria of block ciphers in quantum setting

Some design criteria of block ciphers are already known for the resistance against known attacks like differential, linear , boomerang, etc. Does there already exist any study of design criteria of ...
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Do symmetric and skew symmetric key schedules have any known weaknesses?

A symmetric key schedule is a key schedule of the form $(k_1,\dots,k_{n-1},k_n,k_{n-1},\dots,k_1)$ or of the form $(k_1,\dots,k_{n-1},k_n,k_n,k_{n-1},\dots,k_1)$. A skew symmetric key schedule is a ...
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Encrypting with one key and decrypting with a related key

Given $n$-bit block cipher $E$ (and its inverse $E^{-1}$), define block cipher $E^\prime_k(m) = E_k(E_{f(k)}^{-1}(m))$ where $k,f(k) \in \{0,1\}^n$ and $\forall k:f(k) \ne k$. Under the ideal block ...
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What would be an O(n) time adversary for this kind of scheme

Suppose we have a block cipher $$E:\{0,1\}^k \text{ x } \{0,1\}^{2k} \rightarrow \{0,1\}^{2n} \quad \text{ with } \quad k,n\geq128$$ K is the key generation algorithm that returns a random k-bit key. ...
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Are blockciphers with 64-bit blocks still relevant (in any scenario)?

Facts Blockciphers are used to build encryption algorithms and compression functions for hash algorithms. (Unkeyed) Permutations are also complementing blockciphers in encryption and hashing. Large ...
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Does anybody have test vectors for the LBlock block cipher?

LBlock is a lightweight block cipher with 64-80 bits block-key size, designed by a group of Chinese scholars. Does anybody have LBlock test vectors? I am looking for test vectors, which contain the ...
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LibTomCrypt Documentation on LRW Mode/Tweakable Block Cipher - Apparent Contradiction?

In the LRW mode discussion on page 34/161 of the LibTomCrypt manual, available here for example https://opensource.apple.com/source/CommonCrypto/CommonCrypto-55010/Source/libtomcrypt/doc/...
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Is there any way to encrypt the path in between a small number of 3D positions?

Or more general: given two valid random cipher $c_0, c_1$ a function $D$ with $$D(c_0,c_1) = (a,b,c)$$ should exist but hard to compute (for most cases). The result $(a,b,c)$ represents the path from $...
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Why is confusion & diffusion not required PKI encryption schemes like Elgamal encryption?

The Elgamal encryption scheme is a Multiplicative Mask with the shared key. It doesn't seem to have any confusion or diffusion. So why is it not necessary here as compared to Block Ciphers?
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Is there a universal construction for Davies-Meyer hash functions?

My understanding is that there exists no strong pseudorandom permutation for which the Davies-Meyer construction is known to yield a provably collision-resistant hash function. Were I mean provably ...
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Whats the probability a random cipher has a high probability differential?

This is a bit vauge and long winded. Any partial answers or comments/ways to make this more precise would be greatly appreciated. Fix some general structure for a cipher, for example Sbox then ...
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Why does the random oracle receive much more criticism than the ideal cipher?

The random oracle model seems to be criticized a lot as lacking practical relevance, making wrong predictions, being programmable, etc. However, I have never heard such criticism about the ideal ...
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Attackability of one-time MAC when using block mode

Consider an encrypted message m which is encrypted with AES-CBC, so in addition to the message there is an IV supplied initially....
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Design of SIMD-implemented cipher

Design of efficient of block ciphers needs consideration of many factors such as register size. i found that some ciphers can be SIMD implemented such as TWINE , SM4 , chacha20 ,SPIX ,and others. ...
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Security of bit shift in Serpent

As far I know, the Serpent cipher is the only cipher that uses legit bit shifts (<<) along with circular left shift (...
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How can I determine the Hill cipher key in this case?

I have been struggling with a Hill cipher problem for many days, without any luck. I have the following ciphertext, which I know is an encrypted excerpt from an Edgar Allan Poe story: ...
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Why commutativity gives an invariant subspace?

In A Generic Approach to Invariant Subspace Attacks the authors defined an invariant subspace as: $$F(u + A) = v + A$$ Where $F:\mathbb{F}_2^n \to \mathbb{F}_2^n$,$u, v \in \mathbb{F}_2^n$, and $A$ ...
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Round function in Feistel

Following situation. We got a Feistel network. And in each round we get following outcome on the left side: $$L^\prime = L_1 \oplus F(K_1, R_1)$$ Is there a possible key to get an unchanged outcome ...
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Problems key AES 128 key from last round key

I have written an algorithm in Python to find the main AES 128 key from the last round key. However, it doesn't work; I can not find back my main key. I know that the general principle is to do $w[i] ...
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Using an Even-Mansour block cipher in a tweakable mode of operation

Assume that: $P(X): \{0, 1\}^{\ell_{X}} \rightarrow \{0, 1\}^{\ell_{X}}$. $Q(X): \{0, 1\}^{\ell_{X}} \rightarrow \{0, 1\}^{\ell_{X}}$. $E(K, X): \{0, 1\}^{\ell_{K}} \times \{0, 1\}^{\ell_{X}} \...
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How can I identify the linear equations for a block cipher with 4 different s-boxes?

For a block cipher with 4 different s-boxes (each used in an individual round) how can I identify the linear equations? Normally, for ciphers like AES with a single s-box, linear cryptanalysis can be ...
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Bit slice format of 4x4 s-boxes?

I have studied bit-sliced implementation in SERPENT block cipher and I need to use this technique to implement some 4x4 s-boxes. I couldn't find any procedure to obtain bit-sliced format in any paper ...
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Quantitatively measure the private information revealed by a matrix?

Suppose I have a private matrix $A$ that I want to conceal. I do the matrix multiplication $A^\prime =AK$ and $A^\prime$ is public. How can I quantitatively measure "how well" the matrix $A$ is ...
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Why the same characteristics cannot be used to recover all FEAL4 keys

I am trying to understand how differential Cryptanalysis works. Here I read how to use differential cryptoanalysis for cracking FEAL4 cipher. The big gotcha with this process is that you cannot ...
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New Impossible Differential Attacks on AES reduce time complexity

I am interested in the following snippet from the paper New Impossible Differential Attacks on AES. Analysis of Steps 3–4 of the 7-Round Attack in the 8-Round Attack The most time consuming steps of ...
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Would this 3AES-192 scheme achieve 384-bit key security with just a 384-bit key?

For starters, I don't need any don't-roll-your-crypto stuff. We're discussing a hypothetical. So the idea is 3DES needs 3x the key size and achieves only 2x key size bit security. So using the 3x ...
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Can the requirement to increase rounds with key size be bypassed?

When taking AES for example, the number of rounds increases as the key size increases. This is done in order to adequately diffuse key bits into the state of the cipher. Suppose you replace the AES ...
LightTunnelEnd's user avatar
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Bit based division property

Bit based division property is a great method of Integral attack on block ciphers, which was invented by Y. Todo. According to the paper Bit-Based Division Property and Application to Simon Family (in ...
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Which encryption method support 256 bytes block size?

I am looking at some secret encryption method that apparently uses CBC and a block size of 256 bytes. I can do a chosen-ciphertext-attack. When I modify a single byte in the ciphertext a complete ...
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What mode in EVP for AES-128 should I use for cryptanalysis of AES?

I've been trying to use AES from OpenSSL and got to know that I need to use the EVP-based implementations rather than the AES_*. I need to use AES-128 ...
Luce's user avatar
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How to solve the problem of FHE ciphertext expansion?

FHE typically has large ciphertext expansion factor, meaning that the ratio $$\frac{|\mathsf{Enc}_{pk}(m)|}{|m|}$$ is typically quite large --- in standard schemes it is $\omega(1)$. Even getting $\...
xiao's user avatar
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By using a block cipher multiple times in a row is a 128-bit BC as secure as a 256-bit BC which uses his 128-key only as part of the message?

For given 128-bit numbers $S$ and $E$ we want to find a series of keys $k_i$ with $$ E = BC(BC(BC(.....BC(S, k_1),k_2) ..k_n)$$ We can either use a 128-Bit blocksize block cipher similar to AES (ECB ...
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