# All Questions

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

How to compare the results (e.g. hashed values) of two cryptographic algorithms (e.g. SHA-1 and SipHash) in terms of security? Or is there some other way to do this? That is, how could one prove ...
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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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...
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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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### 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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### 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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...
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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
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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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### Calculation of time needed to crack DES with my CPU

I have a laptop that has the CPU and the RAMs shown below in the images. My question is that, using this CPU and the RAMs, how much time would it take for me to crack an old school DES algorithm ...
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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 ...
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### Twofish vs. Serpent vs. AES (or a combo)

I've seen some posts and info online, but they are from 2009, 2010, 2011 or 2012, which is 3-6 years ago, which is a very long time. So I'm looking for an up-to-date answer about which of these is the ...
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### How obvious is it to decrypt numerics encrypted with a reused one time pad?

For instance say you encrypt text using the one time pad and you end up with some scrambled text that appears illegible. If you reused the key for multiple times for enough text, someone could ...
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### How does $g$ being a generator imply Diffie-Hellman's correctness?

In the Diffie-Hellman protocol for key exchange over an unsecured channel, we choose $p$ and $g$, where $g$ is a generator of $\mathbf{Z}_p^*$. However I want to know why this assumption makes the ...
36 views

### Differences between Work Factor and Time Complexity

I am interested to know if work factor means the same thing as time complexity. Quoting Work Factor : Uncovering keys in cryptosystems The Work Factor of a cryptosystem is related to its ...
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### Would the Fiat Shamir identification scheme be more secure if I design it with an exponents higher than 2?

Let's say both Prover and Verifier would use nth power instead of 2nd when creating public keys and when verifying. I know it would slow it down but would that cause the protocol to be more secure?
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### Working a problem that uses RSA encryption:

To overcome weaknesses of the textbook version of RSA encryption, commonly some form of padding is applied.Consider the following suggestion for an asymmetric RSA-based encryption scheme: Key ...
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I am currently working on my diploma project, a high security NFC door lock and need to exchange very sensible data. That's why I thought of PGP encryption, which is as far as I know one of the ...
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### What would a backdoor in symmetric key cipher look like? [duplicate]

Pretty much what the title says. DES was suspected of having one, but I couldn't imagine what it could possibly look like if only the NSA knew how to use it. Dual_EC_DRBG's backdoor is asymmetric, but ...
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### What are the well known protocols that offer perfect forward secrecy? [on hold]

As far as I know these are the well known protocols that offer PFS TLS/SSL (with DHE-RSA, DHE-DSS, ECDHE-RSA or ECDHE-ECDSA) SSH (RFC4253) OTR (Protocol Version 3 Spec) IPsec (with IKEv1 and IKEv2) ...
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### Runtime of a particular step of karatsuba algorithm [closed]

I am new to algorithms and was trying to calculate the runtime cost of each step of the karatsuba algorithm. Assuming you know what the karatsuba algorithm is, So I was not sure of the calculation ...
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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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### Multiple keys for the same ciphertext [duplicate]

Say you have a plain text: How are you today? and you encrypt it so it becomes: LKD03Loel03skj1Q03 Now you have multiple people that need to know the plain text of this cipher text but ...
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### 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 ...
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### GCM implementation

I want to write GCM implementation myself (only for research purposes). So far, I have successfully written CTR implementation (for AES), but now I ran into few problems with GCM. If I'm not wrong, ...
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### How does knowing the factorization of N can help to obtain the secret?

Assuming $x=a^2 \pmod n$ and knowing $x$, $p$, $q$ how is it possible to obtain $a$?