# All Questions

2k views

### Desirable S-box properties

What desirable properties should an S-box have? My current standard selection process is to just pick them at random and verify that they fit the following criteria: The probability that any random ...
92 views

### Is the difference distribution table of AES S-box uniform?

I am studying about various block ciphers and their weaknesses, so I have a doubt about AES S-boxes, Is the difference distribution table of AES uniform ?
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### Can I discard a specific X509 signature from file?

I'm writing a program to sign files using X.509 certificates and .NET framework classes. My users can sign the same file more than once without any problem (like a revision process). So, a file may ...
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### Meaning of Policy matches when signing SSL certificates

I was going over the process of doing a self-signed SSL certificate. The config file here is one of the inputs to this process (see: https://www.phildev.net/ssl/opensslconf.html) I have a question ...
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### How does the openssl TLS implementation select the ciphersuite?

I would like to ask some help in pointing to me how the oopenssl TLS 1.2 server implementation selects the chosen ciphersuite? Does the server selects the first ciphersuite that is in the server's ...
4k views

### Why is a known-plaintext attack considered a complete break?

I read somewhere that if a cipher has a known-plaintext attack, then it is considered completely broken. Say there is a cipher that someone uses where the algorithm is understood and a known-...
41 views

### What is the logic behind Compress function in iterated hash function

I am working on cryptographic hash functions theorems. In the iterated hash functions part a specific word started appearing constantly: "Compress" for instance within the "compress function". I am ...
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### Do I need output buffer to be multiple of AES block size for CTR mode? [migrated]

In my C code, I use OpenSSL's AES in CTR mode for encryption via EVP interface, that is I have something like this: ...
129 views

### Is solving $m^3 = k*n + c$ hard?

Given the equation $$m^3 = k\cdot n + c$$ I know $n$ and $c$, and I need to find $k$, so that $m$ is a natural number. $n$ and $c$ are large numbers, so i can't use bruteforce. How can you find a ...
61 views

### Is this RSA signing and verification process secure?

I need to verify that messages in a communications program are from valid senders. Below is a highlevel outline of how I think the process would work. The connections themselves are done over TLS. The ...
555 views

### Can elliptic curve (25519) be used to encrypt file?

This is probably a simple question, but I haven't been able to see it stated anywhere. Is it possible to directly encrypt a file (of any length) with some form of EC using the 25519 curve. I know it'...
75 views

### Difference between hierarchical and multi level secret sharing

In this paper, the definitions are simply as follows. Multi-Level secret sharing: Higher level participants can help lower participants to get the secret. Compartmented secret sharing: Each level ...
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### CDH <=> and Square-DH. Square root problem

Here describes a way of proving CDH <=> and Square-DH. The thinkg I don't get - how to efficiently compute $CDH(U,V)$ from $CDH(U,V)^2$. Isn't Square root problem is hard in general? (In case of ...
82 views

### Strange notation using dollar sign

In the paper Multi-Signatures in the Plain Public-Key Model and a General Forking Lemma, the authors Bellare and Neven use notation which looks like left arrow with dollar sign above it. Authors ...
80 views

### Can I calculate $d$ given only RSA’s $c$, $n$ and $e$?

The question “Calculating RSA private exponent when given public exponent and the modulus factors using extended euclid” assumes the factors are known. This got me wondering if it is possible to ...
48 views

### Avoiding doubled letters in encrypted text

I have an encrypted string based on an "alphabet" of 29 runes and access to successfully decrypted (runes->English) plaintext. Testing for a Vigenere cipher, I tried a Friedman attack (aka Kappa test, ...
411 views

### Fast PKI for embedded device

We are creating a device with a small microcontroller (20 MHz CPU 16 KiB RAM). We need some way to securely send signed files to device (only signature, no encryption necessary). An external company ...
45 views

### Do reversible black box obfuscators exist?

We shall say that an obfuscator $\mathcal{O}$ is a reversible black box obfuscator if for each reversible program $P$ the obfuscated program $\mathcal{O}(P)$ is still reversible but does not reveal ...
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### How was the AES MixColumns matrix constructed?

How was the constant matrix in AES MixColumns constructed? \begin{bmatrix} 02 & 03 & 01 & 01 \\ 01 & 02 & 03 & 01 \\ 01 & 01 & 02 & 03 \\ 03 & 01 & 01 &...
18 views

### Extra attributes in a certificate signing request

When creating a certificate signing request, there is a part where openssl says "Please enter the following extra attributes to be sent with your certificate request". One of these is a challenge ...
65 views

### security of using digital signature as key derivation material

I want all keys in my iOS application to rely on the Secure Enclave for security as the iOS keychain becomes insecure on jailbroken devices. Currently, the Secure Enclave currently only supports ...
16k views

### Where i can find an AES implementation in python? [closed]

Where i can find a "reviewed" version of AES implementation in python. Not an API like PyCrypto whereby you can call AES algorithms in a single line.
57 views

### Is a stream cipher similar to One-Time Pad using hash secure?

I've read some Q&A about combining OTP with hash on this site, but I still wonder why some answers said that using hash for OTP key is not strong enough to resist brute force attack? Assuming ...
85 views

### proving indistinguishability of joint distribution using hybrid argument

Using Hybrid Argument, I want to prove following equivalence: $$\{X,Y,Z\}\equiv \{X',Y',Z'\}$$ by proving following equivalences: $\{X,Y,Z\}\equiv \{X,Y,Z'\}$(1) $\{X,Y,Z'\}\equiv \{X,Y',Z'\}$(2) \$\...
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### Why does Paillier have poor performance?

Can anyone explain to me why Paillier crypto system does not provide good performance? I read here (pdf) that RSA and ElGamal provide better performance than Paillier algorithm.