# All Questions

18,453 questions
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### How does the squeeze function in the NaCL Poly1305 implementation work?

The NaCL ref implementation of the Poly1305 algorithm uses the following reduction function (which is called squeeze()): ...
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### Needham–Schroeder fix by adding opponent's identity to the first message

Recap: Needham–Schroeder is as follows: $A \rightarrow B : \{A, N_a\}_{pk_B}$ $B \rightarrow A : \{N_a, N_b\}_{pk_A}$ $A \rightarrow B : \{N_b\}_{pk_B}$ Then, there is a MITM attack by Lowe ...
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### I don't want to store passwords, can I use them as an encryption key for another field?

I'm not a 'cryptographic' anything, so if this is a super-dumb question please let me know (politely). So here's the deal, say I don't want to store passwords because that opens me up to all sorts of ...
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### How to do division using Beaver Multiplication Triples

It is very straight-forward and intuitively to achieve addition, subtraction and even generalized polynomial using Beaver's Multiplication Triples. However division seems difficult to achieve on two ...
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### RIBE Scheme Implementation - How to encrypt message

This question is regarding "A Fully Secure Revocable ID-Based Encryption in the Standard Model" - Tung-Tso TSAI, Yuh-Min TSENG, Tsu-Yang WU The encryption method specifies part of the encryption ...
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### What does XOR mean in regards to AES cryptography? [on hold]

This might be too basic to answer but I am learning about the different modes of operation and I am trying to grasp the material and having trouble deciphering the meaning. I was just wondering if ...
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### Mixed HMAC / GMAC with fixed IV

I was just thinking about improving the performance of HMAC - what would be the issues in doing the following: Let $G_K(IV,M)$ be GMAC with a key $K$, for IV and message $M$. Let $H$ be a secure hash ...
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### Decode location of an RSA encryption message [on hold]

You have intercepted an RSA encrypted message with encoding exponent 7221 and base 5829679010047531. Decode the location: 815427339135043, 5556391338134431, 2892812128428033. I have to find the ...
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### Is it possible to check if a number is the product of two primes without factorizing it?

I have a large number which I suspect may be a private RSA key (although its size, at 613 bits, seems a bit unorthodox). I have started to run a factorization algorithm on it, and after a few hours ...
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### Zero Knowledge for Low Entropy Witness

For any PPT prover ($p$) and verifier ($v$), imagine I have a low entropy witness, say smaller than $2^8$. Now, let us say I have a dlog statement in the form of $y = g^w$. Theory says I could use a ...
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### Cryptography and Security Self Learning [on hold]

I'm an IT developer but interested in Cryptography and Security. Not only I want to learn about cryptography but also want improve my skills for network security job roles. So I was looking for ...
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### Part of a challenge, from a group of adults, who break ciphers [on hold]

I am part of a group of adults, a cipher club who like to decode random ciphers, from texts to symbols and other things. We were presented with a set of 5 ciphered text, and we have managed to crack 3 ...
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### Attack on a Feistel Cipher given the key and half of the ciphertext

Consider a classical Feistel Cipher, with the round functions given and the keys used in the ciphering process. Is it possible to reconstruct the original data if half of the ciphered text is given? ...
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### human readable unpredictable & no collision uid based on time

I need to create an unpredictable uid based on time. I plan to allow it to work during a time frame of 100,000,000 seconds. So the seconds will go from 00000000 to 99999999. I need an algorithm that ...
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I am working on the following exercise: Now, assume the following signature scheme: $KeyGen (1^k$) : On input of a security parameter $k$, choose a symmetric bilinear group with $e : G \times ... 2answers 25 views ### Mathematical explaination of file encryption for multiple persons with multiple keys Let's say I want to encrypt a document which only can be read by John, Mike, and Dave. This can easily done with PGP/GPG: Import John‘s, Mike‘s, and Dave's public key Encrypt the document using those ... 0answers 12 views ### I2P Tunnel Creation Build on Request Record Question en(de)cryption method Not sure if anyone here can help, but if so, sure would appreciate the help. If we read the https://geti2p.net/spec/tunnel-creation documentation page on how I2P creates a tunnel, we can read on the ... 1answer 64 views ### Comparing Shanks' Algorithm to Brute Force I'm trying to understand how/why Shanks' algorithm solves the discrete log problem$y=g^x \bmod p$faster than a brute force search does. Any explanation would be great. 2answers 67 views ### Meet-in-the-middle probability of success In page 358 of Bruce Schneier's Apllied Crypto, when explaining the meet-in-the-middle attack, he states that the success probability is «1 in$2^{2m - 2n}$» with two plaintext/ciphertext pairs, and «... 0answers 22 views ### How to use Windows User Certificate (S/MIME) to sign data [migrated] I am working on an internal ERP for my company. The portal is written in PHP and the current purchasing process is the following: Create a new order on the ERP portal Print the order (PDF) Ask for ... 1answer 101 views ### Curve25519 over Ed25519 for key exchange? Why? I've been reading up on the Signal Protocol (in this PDF) and it seems to be using Curve25519 for ECDH and EdDSA (with Ed25519) for signatures. My question is why not use only Ed25519? This ... 1answer 62 views ### RSA-OAEP Padding scheme Honestly I'm really confused about padding in RSA scheme. I don't study computer science, and I'm a beginner learning cryptography (self-taught). Can anyone give me suggestions? 2answers 48 views ### Self-synchronizing cipher recovery from dropped bits This cryptography book says: There are also asynchronous or self-synchronizing stream ciphers, where the previously produced ciphertext bits are used to produce the current keystream bit. This ... 1answer 51 views ### Does encrypting a result of AES block cipher provide more security? I would like to know if encrypting a result of AES256 block cipher provides more security. Concretely, I am developing a system in which a client sends to a server a ciphertext encrypted with AES256. ... 1answer 81 views ### What is this called: encrypt$X$with key$E$, decrypt$X$with key$D\$?

I am a software developer interested in developing an application with cryptography. I can explain what I want to accomplish, but I do not know the technical terms for the cryptographic functions I am ...
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### Is there an outdated or insecure hash algorithm thats output can be easily reversed back into the input?

I'm looking for a hash algorithm thats output can be reversed back into the input in a reasonable amount of time (a day or less) using a decent consumer computer. If anyone has any information on this,...

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