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 ...

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124 views

Hill Cipher question

Recently, I was given three ciphers to crack for my cryptography class. At this point, I have guessed that one of them is likely a Hill cipher (probably 3x3, as that is the most complex we have done ...
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1answer
375 views

How should I treat a new cipher release like Spritz?

I have been looking at both the paper as well as the sourcecode of Spritz — a spongy RC4-like stream cipher and hash function by Ronald L. Rivest and Jacob Schuldt. The paper states We have also ...
8
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1answer
152 views

Proof of Communication

I desire an algorithm in which Alice sends a block of data $X$ to Bob, with proof that the data was both sent and received. Ideally this would take the form of a public-key signature of the block $X$ ...
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1answer
83 views

Variants of AES? [closed]

Would variants of AES provide the same level of security as AES, say by just replacing the S-box with another one, MDS matrix of Mixcolumn, etc.?
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2answers
133 views

Is this a plausible PBKDF?

Background: Hello, I'm working on a hobby project in which I might want to implement a key derivation function within a somewhat resource limited embedded system. For standard crypto functions, I ...
3
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2answers
290 views

Security issues of a MAC-then-Encrypt-then-MAC approach?

Encrypt-then-MAC does provide ciphertext integrity, but no plaintext integrity. With MAC-then-Encrypt it’s the other way around: Plaintext integrity but no ciphertext integrity. What comes to mind is ...
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1answer
185 views

Implementation and Testing of SRP-6a

I have been wracking my brain trying to develop a functioning implementation of SRP-6a in Python to use with a 3rd-party API that claims to use SRP-6a with $N=$ 2048-bit prime and generator of $2$. ...
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2answers
604 views

How exactly does key whitening manage to increase security?

Wikipedia states that key whitening increases security: In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that ...
7
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1answer
194 views

How many degrees of freedom up my sleeve?

Now that we know how the MD2 S-box was constructed, I find myself wondering how good a nothing up my sleeve number it really is. It is derived from $\pi$, but not in a very obvious way, even in ...
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0answers
68 views

Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
2
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1answer
109 views

How to only encrypt a subset of the plaintext

I was wondering if there is a smart way for a user to only encrypt a subset of a plaintext. I'll try to be more specific. Let's suppose the user U wants to use a special cipher such that given a ...
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1answer
95 views

About S-box in AES

I am working on AES. Can we expand $s(a \oplus b)$ in terms of $s(a)$ and $s(b)$ where $a$ and $b$ are two eight bit inputs and $s(a)$ is the S-box value of $a$?
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2answers
705 views

Reversing DJB2 Hashes

I have some spare time, and a few hundred DJB2-hashed values sitting around. I thought I'd try to do something "useful" and invert DJB2, such that I could calculate the plaintext of the hashes (which ...
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1answer
139 views

Which algorithm do you recommend for practical use to generate unique passwords for each website?

So, in my imagination there is this simple algorithm with only one master password, let's say a prime number 'p', which I have to remember. Using only the address of the website and p, the algorithm ...
1
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1answer
126 views

Rate my idea: is that a stronger GPG-like algorithm?

I came up with a simple idea but I don't know if it is really secure or not. I know that you shouldn't create any algorithm on your own. I'm just curious, that's all. Algorithm explanation: First ...
4
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2answers
102 views

Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
3
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4answers
237 views

Effective security of block cipher – equal the key size, or half the key size?

The Wikipedia “Key Size” article states: The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most ...
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3answers
310 views

In RSA, why does $p$ have to be bigger than $q$ where $n=p \times q$?

In openSSL – during RSA key generation – if $q$ is bigger than $p$, they exchange them. Why is that?
2
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1answer
164 views

How does Web Cryptography API produce secure PRNG?

How does Web Cryptography API (eg window.crypto.getRandomValues) produce secure PRNG? Specifications: https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html#RandomSource-interface ...
3
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1answer
159 views

Math to replace s-boxes - Good or bad idea?

The following was going through my brain for the past week. If my thoughts are generally known to the cryptographic community would someone provide a link or two. Even if I’m making a classic newbie ...
3
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1answer
143 views

Is it a good idea to use Lagrange/Newtonian interpolation for encryption?

I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption? The goal is to reduce database I/O and compute new values on the fly. Suppose the use case ...
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0answers
70 views

A question or few about Mental Poker

I have spent some time studying the "Mental Poker" protocol (sometimes called SRA), initially proposed by Shamir, Rivest, and Adleman -- ...
1
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1answer
90 views

How to adjust scrypt parameters for Moore's Law?

I have been examining the scrypt paper, and I noted the claims in table 1. For 10 random ASCII characters, the cost at that time for scrypt set to $(2^{14}, 8, 1)$ is estimated to be $175T/yr. ...
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1answer
171 views

Where do I truncate the bits in SHA 256 hash algorithm?

I'm implementing SHA-256 in PHP using strings. Where do you truncate in the algorithm? There are a lot of places where there's binary addition happening so the number of bits in $W(i)$ keep ...
4
votes
1answer
96 views

Length-preserving all-or-nothing transform

Is there any known way to construct a length-preserving all-or-nothing transform? In other words, a secure all-or-nothing transform where the length of the output is the same as the length of the ...
8
votes
5answers
360 views

Choose a random number that is different from a bunch of other secret numbers

I'm looking for an algorithm where n participants each have a different secret number between $[0..x]$ (and where $x$ is known) and where the participants then select randomly another, non-secret, ...
3
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1answer
446 views

How to calculate inverse affine transform in AES from forward affine transform?

In AES the forward affine tranformation matrix is defined as: $$ \begin{bmatrix} 1& 0& 0& 0& 1& 1& 1& 1 \\ 1& 1& 0& 0& 0& 1& 1& 1 \\ 1& ...
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1answer
83 views

Algorithm accepting every passphrase to fool unlegit user [closed]

I'm looking for specific names and literature on crypto algorithms that accept every passphrase input by the user, in order to 'decrypt' - even with false passphrase - and present the unlegit user ...
2
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1answer
503 views

Montgomery Ladder vs Double-and-Add

I would like to know what (if any) are the advantages of using Montgomery Power ladder over the Double-and-Add-Always algorithm. I think that firstly, Monty would be slightly faster than DoubleAndAdd. ...