# All Questions

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### How to compare between two cryptographic algorithms in terms of security? [on hold]

How to compare between two cryptographic algorithms (e.g. SHA-1 and SipHash) in terms of security? That is, how could one prove that algorithm X is more secure than algorithm Y?
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### Which characters to take into account when calculating unicity distance?

I need to calculate the unicity distance of a block cipher. Assuming I know that the plaintext is an English message I considered using 53 as the size of the alphabet, since the message could contain ...
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### Multiple encryption of part of block

Is there any security risk in encrypting parts of blocks twice? I'd like to get around block sizes and make encrypted messages just as long as the unencrypted ones: Block 1: Byte 0 - 7 Block 2: Byte ...
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### Is CBC theoretically harder to brute force when compared with ECB?

Theoretically is CBC mode harder to bruteforce when compared with ECB? Assumptions We ignore computational cost for the XOR operations IV is made public
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### AES mode scheme feedback

I've been studying encryption on a hobby basis, and wanted to know if I got this basic cypher construction right (this is another experiment, see the AES ECB experiment thread earlier). Encryption: ...
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### AES key from encrypted text and VI

So I'm trying to figure out if it's possible to extract the private key if you have the ciphertext and the IV corresponding to that ciphertext. It's for some kind of a challenge, and can't really ...
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### How difficult is to key a get using simple XOR

Recently someone gave me algorithim as follows: XOR = Key XOR Random1 XOR Random2. They think that in order for someone to extract "Key" from XOR they would need Random1 and Random2.. but looking at ...
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### Find the prime factorization in the DLP

Suppose we have $g^x \equiv h \pmod N$ Where $N = pq$ and $p$, $q$ are distinct primes. Also $(p-1)/2$ and $(q-1)/2$ are primes. If we know what $x$, $g$ and $h$ are, is it possible for us to know ...
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### AES different modulo operations

I don't get the modulo 10001 operation in mixColumns so much. If I have to take the byte computations mod 100011011 anyway what leads me to a result of 4byte length, why do I need the mod 10001 ...
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### Vigenere ciphers : Need help for math analysis

I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that. This's my method to encrypt : ...
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### Is the reduction from left-or-right IND-CPA to real-or-random IND-CPA tight?

A modern trend in cryptography consists of defining security as rigorously as possible, and then designing schemes which are secure according to those definitions. Proving security comes in the form ...
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### Koblitz encoding a message to a point, what is the “associated auxiliary base parameter”?

I am looking at the Koblitz method for encoding a message as an elliptic curve point. The first step given in the paper I'm reading is: "Choose an elliptic curve and its associated auxiliary base ...
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### How do we compute IV+1 in CTR mode?

This may be a very simple question, but I have not found info about this in any place. My question is about CTR mode: When it says $IV+1$… How do we make this operation? For example, if I have the IV ...
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### Difference between Kerberos and GDOI?

What is the difference between Kerberos and GDOI, I know first is more toward authentication and latter is more toward multicast key management, can I use Kerberose protocol in GDOI for server and ...
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### what are the problems are occur in the revocable CP-ABE scheme in paper of expressive,efficient in multi authority cloud storage [on hold]

and i want what are the disadvantages in the revocable CP-ABE scheme
1k views

### What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
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### N= pq be a product of distinct primes p and q [on hold]

Let = pq be a product of distinct primes p and q such that p1i/2 and q-1/2 are both prime. Suppose you are given N, and you are also given an oracle which allows you to find a minimal solution to ...
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### Consider the congruence x e ≡ c (mod N) [on hold]

Let N be a positive integer with prime factorization N = p a1 1 p a2 2 · · · p ar r . Let c be any integer, and e be a positive integer. Consider the congruence x e ≡ c (mod N).
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### AES as Integer Program

I read that AES can be broken by solving a Linear Integer Program (IP). From a given encrypted text, how can one construct this IP? How big is the system?
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### One-one correspondance complete function

I am reading the paper by John B. Kam and Georges I. Davida (1979) titled Structured Design of Substitution-Permutation Encryption Networks. On page 749 it reads ...
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### What is the advantage of using the socialist millionaire protocol to authenticate vs HMACing some random number?

Say Alice and Bob have a shared secret $s$. Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$, where $r_1$ and $r_2$ are randomly ...
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### Performing differential cryptanalysis for randomly generated S-boxes

As far as I know, performing differential or linear cryptanalysis always requires a knowledge of the S-boxes' content and order. Yet in Bruce Schneier's Applied Cryptography, it is stated that random ...
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### Predicting Google Authenticator OTP Codes

I use Google Authenticator to generate OTP codes for logging in. As you know, the numbers change every 30 seconds or so, and (AFAIK) use an RSA key to generate those numbers. If someone were to ...
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### DH and PKI for KeyExchange

My question is fairly simple. I have more than two nodes which needs to communicate very efficiently from computational point of view. One of the nodes can become a coordinator between the nodes. ...
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I have RTS game, where all players run game and server just relays messages. Game can generate and store text file on player pc. I want to allow some players to be moderators, so I need to sign or ...
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### Will the complement of a 64-bit key and message produce the complement ciphertext if ECB is used in DES?

Say I have a 64-bit message/key: P1: 1011....... K1: 0101....... I run this message/key pair through DES in ECB mode and obtain some cipher that looks like the ...
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### Recombination thresholds in degree reduction of multiplied Shamir shares

Shamir's secret sharing can be considered multiplicatively homomorphic, if one is aware of the fact that multiplying two shares of a (n,t)-threshold shared secret yields a share of the same secret, ...
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### Is Chaocipher a secure cipher under ciphertext-only attack?

Chaocipher was invented by John F. Byrne in 1919. The algorithm was recently revealed – see Moshe Rubin's Chaocipher Revealed, the Algorithm (PDF). While a known plaintext attack successfully finds ...
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### Power analysis and exponentiation by squaring

I am trying to understand how one can retrieve the secret exponent via a simple power analysis. Lets suppose that the exponentiation by squaring algorithm is implemented in its simplest form : ...
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### 128 bit 3DES Key and AES Key: what's the difference?

Apologies if this is really basic but I couldn't find the answer to this. I have heard some Info Sec colleagues talking about creating an AES key in preference to a DES or 3DES key but I don't know ...
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### Signing Files vs. Signing File Hashes

What are the security pitfalls that may occur by signing a list of file hashes, versus signing individual files? In short, the security trade-offs between: ...
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### Is format preserving encryption suitable for use with words or names?

Is it possible to use FPE to encrypt names and language words like 'Bob' 'the' 'tree', in order to preserve both length and format (like keeping characters within a certain range like A-Z a-z) The ...
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### Creating serial key generator using ECDSA, how to get signature short enough?

I've written some questions in this stackoverflow and got great responses but now I'm trying to wrap it all together. I have for the last couple of weeks been building a serial key generator project ...
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### How to choose the integer m in the general number field sieve (GNFS)?

Given an integer you want to factor $N$, GNFS starts by selecting a monic irreducible polynomial $f \in \mathbb{Z}[X]$ and an integer $m$ such that $f(m) \equiv 0 \text{ mod } N$. In practice, if $m$ ...
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### BLAKE2 input parameters [migrated]

Being a newbie, I was reading papers on the recent crop of hash functions and BLAKE2 intrigued me. Then I wanted to play around with the "blake2s" code in the code package. If I were to implement a ...
31 views

### Pseudorandom function and hash function [duplicate]

What is the difference between a pseudorandom function and hash function ? I have already read the answer in this link What is the difference between a hash function and a pseudorandom function? but ...
42 views

### ccrypt and its security

I would like to know how secure is ccrypt to encrypt files (like images, videos and other non-plain text data) using single password of 20+ chars length. It uses Rijndael with 256-bit block size and ...
9k views

### How does RSA signature verification work?

I understand how the RSA algorithm works for encryption and decryption purposes but I don't get how signing is done. Here's what I (think) I know and is common practice: If I have a message that I ...
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### Drawback of ElGamal encryption

I am trying to find out some disadvantages of ElGamal cryptography but I'm not able to figure out what's wrong with the algorithm. The only one I found is that a known-plain text attack is possible in ...
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### What are the steps to decrypt a TLS 1.1 record?

My question is related to another question in Cryptography about TLS 1.1 and 1.2. I have read both RFC 2246 The TLS Protocol Version 1.0 and RFC 4346 The TLS Protocol Version 1.1. What I know is that ...
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### How does ccrypt work?

On many Linux/GNU distributions CCrypt (ccrypt) by Peter Selinger is available as a command line utility to encrypt files. How does the protocol work and is it ...
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### Are there cryptographic schemes that mask as unencrypted traffic?

Are there cryptographic schemes that make encrypted traffic look like unencrypted traffic?
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### Evaluating Algebraic Complexity of a S-box

While studying the design and the desirable properties of an AES S-box , I came to know that Algebraic Complexity is also an important property of an S-box which is usually considered while evaluating ...
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### Possible hashing scheme

Plaintext(binary) : 10101100 //very short for easy understanding Suppose we have 4 predefined schemes/functions, rotate (101 -> 011) flip (1101 -> 1011) exchange (11011 -> 10111) stretch (1100 -> ...
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### Pre-Shared Key tunnel solution? [on hold]

I'm looking for program that will create an encrypted tunnel with port forwarding between two (linux) computers, that handles key exchange using a pre-shared password. In other words, something like ...
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### Why would cryptography fall apart if there were a finite number of primes? [on hold]

I vaguely know that prime numbers are very important in cryptography, but I assume for most encryption methods, they tend to stay rather 'small'. Are we really using massive prime numbers for ...
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### Recommendation for encryption of db fields [on hold]

Looking for java library who is capable to encrypt db fields of postgres 9.x database