# All Questions

61 views

### Which method to generate one time password?

I'm looking for a concrete algorithm to generate one time passwords. The situation is as follows: Alice and Bob exchanged a passphrase over a secure channel in the beginning. They want to ...
66 views

### PublicKey Unknown Encoding

I have a public key: ...
51 views

### Usefulness of ability to calculate $m^{p+q}$ with RSA

I noticed that with only an RSA public key, it is possible/tractable to calculate $m^{p+q} \pmod n$ for any $m$ without knowing $p$ or $q$. Namely, $m^{p+q} \equiv m^{n+1} \pmod n$. (This follows ...
376 views

### Is there a public key encryption scheme with optimal key size?

Symmetric encryption schemes such as AES have known security levels equal to their key sizes (i.e. breaking an encryption with an $n$ bit key needs about $2^n$ work steps). Elliptic curve encryption ...
23 views

### Intermediate values for testing Blowfish

I am trying to implement the Blowfish algorithm in VHDL. To debug my code, I need the intermediate values of s-box and P vectors after each iteration. Where can I find this data set? p.s :- I know ...
140 views

### Is it possible to correct the exponent of an RSA public key if it has been altered?

Is it possible to change the exponent of an RSA public key?
115 views

### With ECDSA is there a way for the verifier to calculate any properties of $k$?

With ECDSA, given $(r,s)$ and $m$, is there a way for a verifier to calculate any (boolean) properties of $k$, without knowing $k$ or the private key $D_A$? (I understand that $k$ should be random, ...
58 views

### How does the size of the prime affect Elliptic Curve Bit Security?

I am using the MIRACL Library to implement an Elliptic Curve Diffie Hellman based Key Exchange according to ECDH-Scheme-Wikipedia. Referring to the Miracl Docs they suggest a few curves. Each curve ...
171 views

### Is there a way to prove equality of plaintext that was encrypted using different public keys?

Imagine if Alice encrypts message to Bob (using public key $P_{bob}$) and then Bob encrypts the same message to Carol (using $P_{carol}$). Is there a way for Bob to prove that: $P_{carol}$ was ...
161 views

### Salary Negotiation Problem

Imagine Alice is applying for a new job. Alice has an idea of the minimum salary that she is willing to accept—let's call this value A. Bob, the hiring manager for ...
197 views

### One Time Pads and reuse of the decrypted message?

How is it insecure when Alice encrypts a message with a One-Time-Pad to Bob, and Bob then uses the decrypted message from Alice as the next One-Time-Pad? For example: Alice sends Bob a message ...
100 views

### Storing a secure key in an embedded device's memory

I am working on an embedded device which send/receive data and stored them in ciphertext mode (encrypted mode ). Now what's best approach for storing Keys (I used ARM CORTEX M series MCU) ? Storing ...
273 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 ...
118 views

### How can you produce visual cryptography?

I would like to be able to "code" images such as the one seen here on Wikipedia. Is this generally produced with software, or does this require complex programming? Ideally, I would love to be able ...
123 views

### Explanation of part of a visual cryptography algorithm

I have been working on a project involving visual cryptography and I am stuck with the following problem. My question is related to this paper, AN IMPROVED VISUAL CRYPTOGRAPHY SCHEME FOR SECRET ...
44 views

### Explanation of vector in Visual Cryptography

I'm starting to study about visual cryptography, but I am stuck with the following problem. On paper "Visual Cryptography" by Moni Naor and Adi Shamir, on page 6. How to read/what is the meaning of ...
43 views

### Can you explain “k out of n” from the VCS paper by Naor and Shamir

I am new to visual cryptography. I’ve just read the paper “Visual Cryptography” by Moni Naor and Adi Shamir and I'm stuck on the chapter about the “$k$ out of $n$” construction. I am aware that, on ...
230 views

### Public Key Encryption using ECDHE and AES-GCM

Using a text book example, Alice and Bob want to communicate securely using encrypted messages over an insecure channel (the Internet). Alice and Bob have decided to use ECDH (using ephemeral keys ...
38 views

### Understanding SSL vulnerability within Apple's GOTOFAIL

Currently learning and reading about the fascinating SSL Key Exchange and came upon the Apple GOTOFAIL incident back in 2014. I'm going through the code during that time and came across this section. ...
401 views

### Algorithm for generating OAuth tokens

I'm trying to find a good algorithm for generating authorization codes, access tokens and refresh tokens in an API. Currently, I am looking into the following setup: Tokens are generated using the ...
683 views

### Is it usual for a signed message to contain the public key of the signer?

In protocols/systems which use ECDSA, is it common for the message to contain the public key of the message signer? If not, how do recipients know that the message has been signed by the correct ...
203 views

The common way to store passwords in web applications is this form: $$hash(password||salt)$$ Does it make sense to store them in the following form instead:? ...
104 views

### How do you communicate the hash function used with RSA signing?

When it comes to RSA signing, I understand why you need to hash the data before signing it, but don't you need to communicate what hash algorithm you use to whoever will need to verify the signature? ...
121 views

### Why are there so many stream ciphers out there and even ongoing research?

What make them better than OTP using a CSPRNG initialized with a secret key?
21 views

### EC algorithm to derive bits/keys and sign/verify [duplicate]

Looking at the question “ECDSA vs ECIES vs ECDH” it appears that you can either have a tool that can derive keys or bits, or can be used to sign and verify something. Is there an EC way to do both ...
125 views

### Possible to guess RSA public key $e$ using $n$ and $\phi$

We know that if $n$ and $\phi$ is known, then it is possible to find $p$ and $q$ (initial prime numbers). I have following the questions: Assume the public key $e$ is not known, how difficult would ...
39 views

### Is it possible and safe to use SAKKE for signing/verification, rather than for encryption?

Is it safe to use the Sakai–Kasahara key encryption algorithm (SAKKE) for signing/verification, rather than for encryption? (Example at bitbucket.org) In particular, I want many Bobs to be able to ...
51 views

### Symmetric encryption with compression for MySQL DB data

I would like to compress data before encrypting and storing it in a MySQL DB to reduce especially bandwith requirements (compression reduces bandwith by 70-80%). At present, all is handled by a ...
396 views

### Are all possible EC private keys valid?

I usually generate a key pair using openssl or Bouncy Castle. I'm using curve secp256k1. The 256bit private keys look fairly random. Do all values of "private ...
232 views

### Should Increment functions be near-constant time?

When operating a block cipher in CTR or GCM mode, should the function used to increment the counter or initialization vector be near-constant time? Here, I'm wondering about the "addition with carry" ...
323 views

### Do Weak Elliptic Curves Exist?

I'm running into very contradictory opinions when try to understand if weak elliptic curves exist. I'm not interested in the case when a curve's weakness is attributed to properties of an EC's prime, ...
722 views

### Is it possible to reduce the size of an RSA key?

The details about what an RSA key is made up of are explained succinctly here. Is it possible to reduce the amount of data that's usually packaged with the (private) key and then derive it later?
139 views

### SHA-256 Hash over multiple SHA-256 Hashes

I am trying to implement a checksum over multiple files. We can assume, that i have a package containing N files. I want to identify such a package uniquely by following calculation: SHA256-Hash ...
374 views

### Developing algorithm for detecting plain text via frequency analysis

First post on Crypto SE, so I've attempted to search the term "English" and looked through the first 10 pages of results, to see if this was a common question, I couldn't find a suitable answer. I'm ...
68 views

### Is it safe to generate ECDSA keys from the hash of the previous, over and over again?

I have memorized a very long and secure passphrase, that when hashed with sha256, I can use the result as an ECDSA private key, and use it as a brain-address for Bitcoin. Now I need more bitcoin ...
115 views

### Why not to use curve over field of $p^m$ with $p > 2$ for ECDSA?

I'm reading the ECDSA paper and they say you can only use ECDSA with odd-power fields $p$ or with binary fields $2^m$. Why not other power prime fields?
582 views

### Nonce role on stream ciphers

Modern stream ciphers usually predicts the usage of a nonce (also termed as IV) in the cryptosystem. The cost of initializing the cipher with the nonce varies from algorithm to algorithm (for ...
63 views

### Making Pascal Paillier' output absolute

Can we make subtraction result of cipher texts encrypted by Pascal Paillier absolute. Just like we use method Math.abs() in Java ? For example, if we subtract 0 from 1: 1-0 = 1, it is positive but 0-1 ...
165 views

### Finding key of AES in ECB mode

How many plaintext-ciphertext pairs would be needed to guess with probability, say $p=0.5$, the key $k$ of AES under ECB mode? Most of the articles that I found tried attacks on single ...
98 views

### Difference between oracle behavior and real execution

Suppose that there is a place in a security proof where the behavior of an oracle differs from the corresponding real execution (for example, the decryption oracle rejects certain types of ciphertexts ...
39 views

### How to use a secret to allow the generation of public keys, where the private keys can be calculated later

Alice has a secret S and publishes some public information P, about S which is insufficient ...
19 views

### What is the bound for the probability distribution for ATV-FHE scheme?

I try to implement the ATV-FHE scheme as described in this paper https://eprint.iacr.org/2014/039.pdf. How do I choose the bound for the probability distribution chi? How do I choose standard ...
17 views

### How to choose moduli ladder for ATV-FHE scheme?

I try to implement the ATV-FHE scheme as mentioned in section 2 in this paper https://eprint.iacr.org/2014/039.pdf. In this paper, authors say this "For example, given a 256-bit prime q ..." in ...
84 views

### Is XTS basically the cheapest form of (secure) double-encryption?

XTS, as given by the below equation, is a mode of operation primarily targeting full-disk encryption scenarios. By the way it works it also doubles the keylength although a meet-in-the-middle attack ...
52 views

### PRF that can be distinguished after $k$ queries?

In adaptive attacks, if we design poorly, adversary can modify his queries and break the given pseudo random function (that is being able to distinguish it from uniform randomness). Is there a poor ...
41 views

### how does the simulator work when the corrupted party has no input?

"the only thing the simulator can do in the ideal model is to choose the corrupted parties' inputs." Yehuda Lindell said. 1- what will happen when the corrupted parties have no inputs to the ...
489 views

### Which is/are the strongest known Fully Homomorphic Encryption scheme(s)?

As it is discussed here that the highest security any homomorphic encryption scheme is at most IND-CCA1, Is there any known fully homomorphic encryption scheme that achieves this security level? Out ...
31 views

### How to generate public key for ATV-FHE scheme?

I want to implement the ATV-FHE scheme as it is described here https://eprint.iacr.org/2014/039.pdf. How to generate the public key? Should I compute it as indicated in section 2 : \$h(i) = ...