Questions tagged [algorithm-design]

Design of cryptographic primitives (algorithms), like block ciphers, stream ciphers, random-number generators, hash functions, MACs, key exchanges, public-key encryption or signature schemes. Also tag with the relevant type of primitive. If you ask about a known existing algorithm, also tag with its name.

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3
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1answer
472 views

Is modular Barrett reduction usable for Ed25519?

I currently try to implement Ed25519 following this draft. I have implemented every field operation except the reduction by the group order $q$ (in chapter 5). I looked for a reduction algorithm and ...
9
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1answer
318 views

Why is the whole initial state used in the final addition of Salsa20 and ChaCha?

Both Salsa20 and ChaCha basically work like this: Put the key, the nonce, the sequence number and a constant into a 4x4 matrix of 32-bit words. Transform the matrix invertibly with a number of ARX ...
5
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0answers
102 views

search of patterns in key schedules

I am developing a new key schedule, and there is this article (Enhanced Key Expansion for AES-256 by Using Even-Odd Method) where the authors also propose a new algorithm and one of the objectives is ...
5
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2answers
4k views

How to prove that a function is not pseudorandom?

I am currently enrolled in a cryptography course, which uses the book by Katz and Lindell. I'm struggling with the exercies which ask for proofs, like the following one: Let G(k) be a PRG with |k| ...
2
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4answers
4k views

What is k in RSA?

I am currently learning about RSA since I didn't understand the public-key-system but now I am… kind of. So I am writing the numbers as follows: $p = prime\ number\\ q = prime\ number\\ N = Public\...
3
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0answers
237 views

How can I design a cryptographically secure, key-dependent s-box?

I would like to design a cryptographically secure, key-dependent s-box, but I am not sure how. Mainly, because I am unsure about the difference in design compared to a random s-box. What is the ...
4
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2answers
208 views

Why should $a,b < N$ for Montgomery Reduction?

In Montgomery reduction, when calculating $a \times b \mod N$, it is required that $a \lt N$ and $b \lt N$. I think $0 \le T \lt N \times R$ is enough for the Montgomery Reduction. Rationale: Let $a'...
2
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2answers
780 views

Question about the key in RC4

I am planning to develop a more secure version of the RC4 algorithm. Since I´m not an encryption expert, I´ld like you to help me find answers to the following questions: Does the value of the key ...
4
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1answer
210 views

Improve security of transposition ciphers

As we know, breaking a Transposition Cipher is quite trivial and can be easily done by either exploiting single letter frequencies (not $d$-gram frequencies though, given that $2 < d < L$), or ...
3
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1answer
700 views

Has anyone heard of matrix-based “Russian Doll” encryption techniques?

I've been told that prime-number factoring is based on a "russian-doll" sequence of matrices, where a seed matrix of height Y and width X exists consisting of all zeros except for a single 1 at row Y ...
12
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1answer
483 views

Why isn't outputting only a portion of the hash state a simple defense against length extension attacks?

As I understand length extension attacks, they depend on the coincidental property of most cryptographic hash functions that the hash value is exactly the hash function state after hashing the last ...
4
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0answers
232 views

IES: What security has the asymmetric primitive to provide?

I think most of us know the notion Shoup introduced of KEM/DEM (Key Encapsulation Mechanism / Data Encapsulation Mechanism) which is used for example by the (famous) ECIES, where the key is the hash ...
6
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1answer
526 views

One cipher to rule them all?

I learned from Dan Boneh's course that many cryptographic primitives (prngs, stream ciphers, hashes, hmac, key derivation functions) can be built from just one a block cipher or PRF. For example, the ...
8
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1answer
811 views

Why have round constants in hashes?

This may seem like basic crypto knowledge, but why do hash functions like SHA-2 and Whirlpool have round constants that are absorbed into their respective states? I can understand that in a cipher ...
4
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3answers
646 views

Reasons for components of AES

I started reading "Cryptography: theory and practice" by Stinson, and I am trying to understand the reason behind the choices for the different components of AES since they seem quite arbitrary. In ...
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0answers
100 views

Fast mental encryption algorithm? [duplicate]

Are there any algorithms that exist to encode messages written with pen and paper such that the messages can be encrypted/decrypted mentally? For example, Bob thinks of the text "This is my plaintext",...
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1answer
117 views

Is algorithm with more than $2^{word size}$ words secure? [closed]

Let's say we have a feistel cipher or feistel pseudo-random permutation with 8-bit function (S-box) similar to Treyfer, but with much bigger block size like 16MB. Here is example of such pseudo-random ...
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2answers
112 views

Concerns about use of MAC in my specification

Here is the pseudocode for a routine I am designing: ...
25
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4answers
5k views

How do we know a cryptographic primitive won't suddenly fail?

It took more than a decade from when MD5 looked like it was going to break to the point when it was actually broken. That's more than a decade of warning. One might suspect that we were fortunate that ...
3
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1answer
1k views

How was the MDS matrix used in AES chosen?

$$\begin{pmatrix}2&3&1&1\\ 1&2&3&1\\ 1&1&2&3\\ 3&1&1&2\end{pmatrix}$$ In the above MDS matrix used in AES encryption, why are the numbers $2$,$3$ and $1$...
3
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1answer
205 views

LED cryptography algorithm

I would like to better understand the operation of the LED algorithm, especially the process of substitution and permutation of the blocks and especially the use of the keys in each round. The keys ...
1
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1answer
358 views

Why doesn't this defeat RSA?

Apologies for the obviously ridiculous question but I need to know where I'm going wrong here. For RSA, we compute $n=pq$ for primes $p$ and $q$. We then choose an $e$ such that $gcd(e, \varphi(n))=1$...
2
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2answers
625 views

Why are there no OTP ciphers?

We all know the OTP is unbreakable and we all love the OTP (judging by the amount of question on this site). The strength of the OTP is not that it is unable to find a word without the key but you ...
3
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1answer
151 views

Image sharing without data overhead

The idea is to share $n$ images among $n$ persons so that all images can be reconstructed by someone in possession of all shares. However, there must not be any data overhead (which means the shares ...
4
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1answer
170 views

Is this transposition cipher information-theoretically secure for 1 message?

Given: $m = \{0,1\}^{n}$; a plaintext message of length $n$ encoded in binary $k = randomshuffle([0, 1, ..., 2n-1])$; A secret key consisting out of unique numbers between 0 and $2n-1$ in a true ...
8
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0answers
347 views

Is the key schedule of Serpent a circle?

The creation of the prekeys for Serpent works by XORing some previous values with a counter and a fixed value. Every word is 32 bits big and 4 words form a round key (after applying a S-Box, but this ...
1
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1answer
3k views

Affine transformation in AES: Matrix representation

I know that the affine transformation of the AES can be represented both as a polynomial evaluation over $\operatorname{GF}(2^8)$ and as a matrix-vector multiplication (see, e.g., p.212 C.4 of The ...
3
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1answer
666 views

What does “invertibility of the cryptographic primitive” mean?

source: http://www.cosic.esat.kuleuven.be/publications/thesis-152.pdf ,page 32 Note that key recovery implies invertibility of the cryptographic primitive (because due to the Kerckhoffs’ ...
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1answer
392 views

Creating a new cipher! [closed]

http://flashbackcipher.blogspot.ae/2015/03/introducing-flashback.html Hey guys the above is the blog for a new cipher, if you guys can take a look and suggest problems.. it would be of great help!! :...
3
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0answers
238 views

How to calculate the non-linearity of an s-box? [duplicate]

I am struggling to understand how to calculate non-linearty of an s-box, could someone show me a detailed example? I found “How to calculate non linearity of AES S-box?” which helped a little, but I ...
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2answers
1k views

Self verifying hash algorithm

For quite some time I've been thinking about the idea to construct a hashing algorithm that contains its own checksum value, and thereby can verify itself. With hashing algorithms like SHA1 and MD5 ...
1
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1answer
2k views

Why is AES unbreakable?

Why is it said that AES is unbreakable? Brute force attacks would take years to crack it, so is it possible to crack it if the computational speed of machines increase in the following decade?
-4
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1answer
281 views

how to integrate 2-3 algorithms to encrypt large data fastly and securely insted using AES? [closed]

I am thinking to build an encryption algorithm which take less time when encrypt large data such as video,mp3 and which has security credential.
0
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1answer
368 views

Vigenere ciphers : Need help for math analysis

I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that. This's my method to encrypt : ...
1
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1answer
105 views

Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob. Bob stores the decrypted message and the digital signature in a database. However Alice is a bad girl and ...
1
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1answer
101 views

Is there a reference that prove that the AES Key Schedule generate random looking round keys?

Starting from uniformly random generated AES master key, is there a reference that prove that an specific roundkey can be considered as uniformly random generated as well ?
2
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1answer
4k views

How to implement HMAC SHA-256

I am trying to figure out how the HMAC SHA-256 hashing algorithm works. I know that we have to use the following: H (K ^ opad)|| H ((K ^ ipad)|| text)). The ...
8
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2answers
3k views

Where are the ChaCha20 test vectors/examples?

I see in the Salsa20 specification there are test examples throughout the document to help an implementer make sure every function works as designed. Consequently the whole algorithm would work ...
0
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3answers
512 views

Random Galois fields

Note: I have now answered this by my own research and can generate random fields up to G(2^9) in reasonable time. I would need to find more speedups for larger fields. At this time G(2^8) takes a few ...
0
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2answers
132 views

Is my method symmetric encryption?

To obfuscate data I made up this method on the spot without planning since the goal wasn't real encryption. At first I though this cannot be real encryption but after revisiting the code and reading ...
4
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1answer
1k views

Diffusion in Stream Cipher

The diffusion property of a cipher defined by Shannon refers to the ability of a cipher to cause a lot off bits in the cipher text to be modified, when even a single bit in the plaintext is flips. ...
6
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2answers
2k views

What makes an algorithm “fast in software” vs. “fast in hardware”?

When reading about different algorithms, I often encounter claims that various algorithms are "fast in software" (e.g. Salsa20) or "fast in hardware" (e.g. DES). What properties make a cipher ...
13
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1answer
2k views

Dancing confusion with Daniel J. Bernstein's stream ciphers

I know of Salsa20 which won the ESTREAM competition. This is dated of 25 Dec 2007. There is also the ChaCha20 stream cipher (cr.yp.to/chacha.html). This claims to increase the amount of diffusion ...
0
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2answers
590 views

What would be the best plain text Cryptography method without the use of a computer? [closed]

What would be the best Cryptography method without the use of a computer? This could be a list of the current options available, that could be used without the use of a computer system/electronic ...
1
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1answer
141 views

MD-compliant hashes don't really accept arbitary length input, do they?

When people talk about hash functions, they usually say that they accept arbitrary-length input, but if you actually look at the padding (eg MD-strengthening padding), you see it's like M100.000||...
0
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1answer
117 views

What cipher algorithm is this routine using? [closed]

I transfered a code routine from Java to Python: ...
0
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1answer
93 views

How to establish if a string contains a message

If you have a string S, then the string can be composed of four things: cleartext 'random' data encrypted data compressed or otherwise non-encrypted, but modified, cleartext If you want to see if ...
5
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1answer
547 views

Do data-dependent rotations have any advantage over fixed rotations?

There are many ARX ciphers, however most use fixed rotations. I know data-dependent compared to fixed rotations are: patented (expired) harder to implement constant time more expensive in hardware ...
2
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0answers
255 views

How can I start the following crypto project? [closed]

(Cryptography: encrypting files before storage in the cloud): The project consists of a software implementation of a method to pre-process a file before storing it on a cloud storage server so that ...
2
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2answers
338 views

Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you have ...