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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What is the exact algorithm for encryption and decryption with hummingbird-1 cryptography?

I have really googled the entire internet but could not find a clear algorithm for hummingbird-1 cryptography.The problem emerges in the decryption module: What is the initial value of state register ...
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How to apply a block cipher to (large) packetized communication when packets can get lost/erased?

In light of current events (Zoom getting strong headwinds for using AES-128 in ECB mode), I was wondering what the general approach is to packetized data encryption, where the packet length (UDP for ...
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Is there any software available online for checking the properties of substitution boxes for block ciphers?

I have designed a s-box and now i want to find out its properties i.e. what are the values of non linearity, SAC, BIC etc?
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Why do people criticize and mistrust the e-voting based block chain?

I am planning to implement an e-voting system based on hyperledger fabric blockchain, however, I came across many criticisms from well-known security experts like Josh Benaloh and others. The problem ...
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A possible error in the book

So I have been reading this book called "Implementing SSL/TLS using Cryptography and PKI" While going through it, this snippet of code got me baffled ...
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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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How do I find out whether a message in CBC has padding?

When a program is decrypting a message encrypted by CBC mode, what does it find out, whether the last bytes of the last block is part of the padding or part of the plaintext? Example: Use CBC mode ...
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Why mining bitcoins is difficult?

As I understand to obtain a Golden Block is to finding a nonce that matches a hash lower than a given target, as shown in this research-gate article. And here is a "py" kernel: Bitcoin mining python (...
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How to break CBC cipher with partly known plaintext?

I'm learning some IT security and during practice I found an exercise I couldn't solve. I have an encrypted message with block cipher in CBC mode. The blocks are one byte long and the first block is ...
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Is there any practical use of reduced rounds of AES

There are lots of attacks which are on reduced block ciphers. There are practical attack on five rounds of AES-128five rounds aes broken in six minutes. I was just wondering if there is any practical ...
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How to prove IND-CPA on a cipher [duplicate]

I came across an exercise "custom" block cipher which looks like a counter mode implementation, but it is not exactly it. I want to check if this scheme is IND-CPA secure. Here is a picture of the ...
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Correlation power analysis attack on Camellia

I'm investigating a correlation power analysis on a black-box ASIC I have. I want to learn about correlation analysis and it seems this ASIC implements Camellia. I searched for researches that did ...
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Longer IV generation from a single block IV for ICBC

I was reading a question about ICBC here and it mentioned that you would need a $s \cdot n$-bit $IV$ if you would use $s$ "stripes", where $n$ is the blocksize. Say that we don't like transmit that ...
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Interleaved CBC

I've been researching cryptographic modes and came across an obscure mode called interleaved CBC (ICBC). I can't find a lot about it and am wondering if anyone knows anything more. It's basically CBC ...
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18 rounds encryption in embedded?

I have a power trace of a decryption. It seems like I'm watching a 18 rounds decryption algorithm. I cannot think about any other algorithm implemented in ASIC except Cammelia who has 18 rounds. ...
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Lai-Massey scheme

One rationale for Lai-Massey design is to achieve full diffusion in a single round compared to SPN and Feistel (hence less rounds number) due to use of multiplication-􏰅addition (MA) function. However ...
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Is CTR really equally secure than CBC?

Here is a typical cryptographic situation: A secret key exists that is only known to a sender and a receiver of messages. As it is hard to replace that key, since you either need a secure channel for ...
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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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Is a larger block size less secure against a brute-force known cipertext attack?

Suppose a ciphertext $c$ was encrypted from plaintext $m$, and we know something about the form of $m$; say, for example, that $m$ is English text. We can attempt to brute-force $m$ from $c$ by ...
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Why didn't people redesign the key scheduling algorithm of DES to use longer keys instead of using 3-DES?

To overcome short key length of DES, Triple DES was devised. What would go wrong or why didn't people redesign the key scheduling algorithm to use longer keys?
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How keeloq keyfob exchange key with receiver in the first place?

After reading a lot of articles and the microship maunal for keeloq IC, I think I understand how the encryption and decrytion works. If I understand correctly, however, the decryption require the ...
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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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Would using perfect S-boxes in F function of an unbalanced Feistel network produce a simple and secure cipher?

When I read some articles about cryptography on wikipedia, I took note of the following statements (please, correct me, if any of these are wrong): Perfect S-box (based on bent functions) provides ...
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What are the general rules to follow if I want to design a block cipher suitable for file encryption? [duplicate]

Can you please tell me what should be the quality of an encryption function using a key size of 256 bits... I realized from my previous question that a simple XOR of plaintext (256 bits) with a ...
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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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Serpent vs AES,, theoretical security

In the lets-choose-the-next-aes contest in 1998, they chose Rijndael because of speed. Now, not taking speed into account, is Serpent more secure or not? Since it has 32 rounds (of course that's not ...
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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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2DES and 3DES against a DES build with complimentary

I saw this complicated question and I am not really sure about it, would appreciate your view on it. Is the following build stronger than 2DES or 3DES with 2 different keys (or even normal DES)? $...
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Simple block cipher

I came up with this concept, which I thought would be pretty secure. So the idea is this, you have a message $M$, which you split up in blocks of each 256 bits. You generate a random (pseudo-random ...
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How to perform ByteSub transformation? [duplicate]

Can anybody please tell me how do we perform ByteSub transformation of AES to 01001001.
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What will be appropriate AES padding characters?

I am completely noob in terms of cryptography and security. So I decided AES Cipher for encrypting my data. I pad my input data String with blank white spaces to fit it in multiples of my cipher ...
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A bit-sliced implementation (or the algebraic normal form) of the two FIDES S-Boxes

I want to see a bit-sliced implementation of 5-bit and 6-bit S-Boxes of FIDES or, at least, a representation of these two functions in algebraic normal form. Where can I find it?
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How can AES-CCM behave as an AEAD stream cipher?

AESCCM- Couter with Cipher Block Chaining Message. As it uses cmac for generation for tag , which is internally aes-cbc (block cipher, need block size, may require padding) And Encryption is done ...
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Colliding input to compression function

So I recently started to look into cryptography and found the following question to cryptography scheme using $T = E_{S}(S \oplus M)$ It is said that this is not secure because you can have a ...
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Block cipher mode of operator with counter as part of its key or message [closed]

Consider a block cipher (such as AES256) as $E$, a randomly selected key $k$, a counter $i$, and an array of n-bits $M$ as the message. Also consider the following block cipher modes of operations: $...
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How can frequency analysis be applied to modern ciphers?

I am building a computer program that deciphers Caesar, Vigenere and monoalphabetic substitution ciphers. All of those are susceptible to frequency analysis. However, it does not seem to be real-world ...
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Perfect Forward Secrecy Stream Cipher based on Block Cipher

I'm thinking about ways to encrypt an endless stream of data (e.g. a video or audio feed) in a way, where a compromise of the current internal state of the encryption (e.g. a RAM dump) does not ...
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Is there a name for encryption which relies on repetitive calculation (=time) instead of a key-value? (e.g. block chain, hash value, block cipher)

Many encryption problems are fast to solve if a key, factor, exponent or something similar is known. Other encryption methods don't have such keys. E.g. a hash value of another value. It's used ...
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Why is ECB+CTR not a thing?

AES-CTR is nice for its parallelizability and simplicity but if you duplicate an IV you reveal plaintext. Chaining modes like CFB and CBC don't have that problem per se but they are not ...
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Is there a 'chain-function' which allows computing the value for the index which is next, previous, +/- some constants but has no shortcut for other?

Looking for an algorithm which has a cyclic 'chain'-function which only allows the computation of next, previous element and in addition to that also a shift by a small amount of constants. Example 1 ...
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8 bit block cipher in CTR mode for practice - counter is 32 bits

I'm given a very simple 8 bit block cipher in which to encrypt plaintext x with k k one performs $ x \oplus k $. I am given IV = 0101 and a CTR of value CCCCCCCC (36bits). My understanding is that ...
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Do any block cipher encryption functions (or similar functions) exist which are associative to each other and cyclic?

Most block ciphers encrypt a plaintext deterministically into a ciphertext which allows decryption in the opposite direction. Now, instead of encrypting just one plaintext, I'm looking for a cyclic '...
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Block cipher linearity (in relation to hill ciphers)

So while I knew hill ciphers were a form of block cipher (I'm assuming all the ones I have solved to date were ECB or something similar), so that got me thinking. Is it possible to use hill ciphers in ...
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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?
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Attacking Double DES (OFB Mode) given the initialization vector and not much else? [closed]

I'm given a Plaintext/Ciphertext pair, a Ciphertext to break, and the IV. One thing of note is that the same IV is used for both DES Encryptions, so $$C = E_{K_2}(E_{K_1}(P, IV), IV)$$ I have limited ...
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Do there exist cryptographic algorithms where the “core” function is 96-to-32-bit?

There exists a FOX family of block ciphers (Wikipedia article: IDEA NXT). This cipher uses a function called "f32" which operates on three 32-bit words and outputs one 32-bit word. This function ...
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Are slide attacks effective if the primitive is sandwiched? And key schedule vs. Even-Mansour

Suppose you have a cryptographic permutation consisting of identical rounds, that makes it vulnerable to a slide attack. But if you sandwich it between two XORs of key material. Is it still vulnerable?...
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Why does error propagation in CBC mode encryption affect two blocks?

From Wikipedia: Error propagation It was common to discuss the "error propagation" properties as a selection criterion for a mode of operation. It might be observed, for example, that a one-...
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Are any block ciphers provably free of equivalent keys?

There are $2^n!$ possible permutations of an $n$-bit block cipher $E_k:\{0,1\}^n \rightarrow \{0,1\}^n$, and any given key $k$ selects one of these permutations at random. Define equivalent keys as a ...
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What security risks does exposing the size of the plaintext entail?

For this question my focus is exclusively on symmetric block ciphers (with a particular interest in AES256 in CBC mode). I have read much discussion on various ways to pad the plaintext so that the ...

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