# All Questions

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### Probability of SHA256 Collisions for Certain Amount of Hashed Values

I wonder if you can help me figure out that question: Is there a known probability function f: N -> [0,1], that computes the probability of a sha256 collision for a certain amount of values to be ...
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### Does revealing shares of the result reveals shares of the inputs?

Suppose Alive and Bob have shares of two polynomials $P,Q$, say, Alice knows $P_A,Q_A$, Bob knows $P_B,Q_B$ s.t. $P=P_A+P_B$ and $Q=Q_A+Q_B$. They perform some operation $f$ over the shared values, to ...
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### Camellia Key Schedule Sigmas [migrated]

Camellia uses 6 sigmas in its key schedule with values ...
3k views

### What stops the Multiply-With-Carry RNG from being a Cryptographically Secure PRNG?

Despite the fact that Marsaglia's MWC PRNG (multiply-with-carry random number generator) is considered to be "the mother of all RNGs", it does not seem to be considered to be a CSPRNG (...
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### Are there any digital signatures valid for multiple pieces of data?

Are there any digital signature algorithms that can be used to produce signatures valid for multiple pieces of data? For example, pick a private key k, which has ...
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### Does there exist an indistinguishability formal proof obfuscator?

A formal proof obfuscator is a mapping $\mathcal{O}$ such that whenever $P$ is a formal proof of a theorem $T$, then $\mathcal{O}(P)$ is a distribution of formal proofs of the same theorem $T$. An ...
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### Syllae algorithm and Malaysian cipher from Rubicon

In the first episode of a tv series Rubicon (exactly in 482 and 491 lines of an English subtitles) there is mentioned Syllae algorithm and Malaysian cipher. I could not find any details about these ...
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### Is security against semi honest adversary inheritable?

I have a two party protocol, let's call it $M$. At some point, there are $k$ steps, each one involving an oblivious transfer protocol, which is known to be secure against semi honest adversaries. ...
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### Public key decryption mathematical analogy

To clarify, I'm talking about digital-signatures, not public key encryption. When I encrypt something with a private key, then it should be decryptable with a public key, as I've understood how ...
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### what are the kind of mathematical proofs that i need to be familiarized with to understand (or do) cryptography? [on hold]

I know reductions are highly used to show that encryption schemes are secure under certain conditions, but i don´t know what other math proofs are needed. PD: English is not my native language so ...
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### Problem when programming Schnorr signature

I have some questions about Schnorr signature implementation. I am trying to implement it in C++. I chose private signing key x and public verification key y = g^x. I have a message M, random number ...
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### How are keys stored in a .keystore file or in a .jks file?

I would like to know what is the structure of the keys stored inside a .keystore or a .jks file? by structure I mean are the keys stored in key value pairs? how are the passwords for several keys ...
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### How can I convert an image into a long hexadecimal code and vice-versa? [on hold]

Title. Characters to fill required 30 characters minimum.
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### Quantum circuit to implement McEliece cryptosystem

I've come up with the proposal of implementing McEliece cryptosystem with the help of quantum gates and quantum programming, creating a circuit to do the encryption based on the McEliece original ...
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### How would low-precision Gaussian sampling impact the security of BLISS?

For digital signature, I implemented BLISS in my cryptographic suite, and wrote the Gaussian sampler based on Lattice Signatures and Bimodal Gaussians. But unlike the reference implementation and ...
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### Using master password to encrypt and decrypt user credentials

I need a way to store third party credentials, and I want to avoid storing passwords in plain text. I can't use a hash because I will need to be able to get the raw password to log in to the third ...
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### ocf-linux, Splitting large buffers into chunks < MAX_DATA_LEN [migrated]

I am using ocf-linux in an openwrt application and have run into OCF CRYPTO_MAX_DATA_LEN (64K-1) and E2BIG errors in CRYPTO_AES_CBC mode. As a consequence, I need to split the input buffer into ...
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### Applying machine learning algorithms to homomorphic encrypted data

I have a basic understanding of encryption and I got back to the topic because of an interesting site that encrypts financial data using homomorphic encryption (HE) and I would be happy for any input ...
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### Do I need to prove this?

I am using ABE scheme that has already proven under BDHE assumption. Here is the scheme https://eprint.iacr.org/2008/290.pdf In the key generation algorithm, I want to tie the user secret key ...
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### Is there a PRNG algorithm that allows to switch between states directly, not calling next()?

Basically I need a function with the following interface: getRandomBytes(uint128 seed, uint64 state, uint16 byteCount) Consecutive calls with the same seed and ...
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### Is it ever safe to use encryption with compression?

In the wake of compression-based side-channel attacks like CRIME and BREACH, are there any safe ways to combine compression and encryption? The JWE Specification was finalised almost 2 years after ...
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### Why is it so hard to make longer hashes?

I was reading this answer about why there is no such thing as a SHA-1024 hash: SHA-2 was built with state and word sizes to meet the security requirements on commodity computers (x86 and Alpha), ...
188 views

### Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
281 views

### PGP String-to-Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
293 views

### Reusing message in One Time Pad

One of the main rules of the OTP is, that a key should never ever be reused. But if we use some commutative operation (XOR for example) for generating the cipher text, then I don't see any difference ...
28 views

### Secure logical AND using Ishai-Sahai-Wagner Scheme

I want to try to implement a secure AND the way it was described here: https://eprint.iacr.org/2010/441.pdf It says that there are two bits a and b and that they have been split into d+1 shares. How ...
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### Initializing PGP keys by one side

I am using a PGP method to encrypt and decrypt messages shared between users A and B. Upon the start of a message exchange is the initialization of the public and secret keys by both Users. Lets say ...
37 views

### Independence of answers to queries sent to a random oracle

Assume we have an algorithm which asks random oracle $\mathcal{O}$ $Q$ queries $u_1, \ldots, u_Q$. All queries are unique, $u_i \neq u_j$ for $i \neq j$. Queries $u_i$ are random variables, too. What ...
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### Is there any functional encryption scheme whose key generation circuit is in NC1?

To my best of knowledge, I have kown there exists randomized encoding scheme whose encoding circuit is in $NC^1$, fully homomorphic encryption scheme whose decryption circuit is in $NC^1$, and ...
38 views

### RAR brute force cracking speed

I have been playing around with cRARk and was astonished by the low speed. On a 2015 high-end GPU (GeForce 980 ti), it took roughly 4h 50min to test all passwords composed of an 8-character prefix and ...
5k views

### Why has the RSA factoring challenge been withdrawn?

Wikipedia states that RSA challenge has been withdrawn. Does it mean that an efficient factoring algorithm is "just around the corner"? or are there some other reasons? If the challenge was still ...
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### Choosing between RLWE-KEX methods.

Recently, I've been researching and implementing a bit of post-quantum cryptography, and I came across two RLWE-KEX algorithm for key exchange. The first one, which I implement in my software, is ...
2k views

### Can a shift cipher attain perfect secrecy?

On a practice question for my intro cryptography exam, it asks the following: Assuming that keys are chosen with equal likelihood, the shift cipher provides:    A) computational security ...
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### How to measure ECC key size?

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
32 views

### How do Raptor (Fountain codes) encoding and decoding work? [on hold]

As described in this article, a Raptor code is a fountain code that encodes a message of $k$ symbols into a limitless sequence of encoding symbols, such that knowledge of any $k$ or more encoding ...
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### Decomposing an ideal in intersections

Let $R$ be an ring, and let $(a),(b)$ be the ideals generated by $a,b\in R^\times$ respectively. Let $c=a\cdot b$ and $(c)$ the ideal generated by $c$. I am supposing that, given $c$, it is ...
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### RSA: revealing the modulus factorization by choosing a bad message

I started reading the book Cryptanalysis of RSA and its variants by M. Jason Hinek and I stumbled upon a phrase that intrigued me: plaintext messages that are relatively prime to the modulus (i....
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### Security of a self-decrypting block-cipher?

If I have a block-cipher like for example AES, a plaintext $x$, we use different function to encrypt and decrypt : $\text{encrypt}(x) = y$ , $\text{decrypt}(y)=x$. Now, if we build a function with a ...
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### Why is it OK for secretbox to leak the message length?

Most block cipher implementations expect users to pad so that the message matches the cipher block size. I understand the purpose of the padding is to make the input match the cipher block size. It ...
73 views

### How to design a balanced LFSR with period 1023 and linear span 55?

I am trying various combination of LFSR's to try to design sequence of period 1023. The linear span should be 55 and the output 1023 bits has to be balanced. I have tried with five LFSR's with degree ...