# All Questions

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### Polyalphabetic rotation cipher over digits

what is the keyspace of a poly-alphabetic rotation cipher over digits, with a repeated key-length of 2, in which no digits can encrypt to itself? Why is the answer 72?
25 views

### Hash functions producing 48-bit hash?

Could you please list hash function algorithms producing 48-bit hash for checksum?
25 views

### Why doesn't WhatsApp encryption multiply file size

WhatsApp uses and end-to-end encryption, on both personal and group chats. According to my understanding, that means every message I send to a group is encrypted on my Device for every group member ...
25 views

### What hash function? [on hold]

input: "HqDkJnxGdf.NjNQnTxaeC41pwi0WDvD6Rl2a7-GnfxY.35303.34720" hash: acdf608df8b8 input: "HqCELbAzF2.NjNQnTxaeC41pwi0WDvD6Rl2a7-GnfxY.34326.34720" hash: 742f26dd9e14 input: "HqCELbAzF2....
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### Order of subgroups formed by Elliptic Curves with a Cofactor

In this question: Why are the lower 3 bits of curve25519/ed25519 secret keys cleared during creation? The answer indicates that the order of all points on the curve over the finite field ...
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### Does SET in any way use SSL?

I just started a course in web security, and I was just wondering quickly if SET in any way would use SSL? I noticed it was developed in part by Netscape. But all I can find is comparisons between the ...
16 views

### How to perform ByteSub transformation? [duplicate]

Can anybody please tell me how do we perform ByteSub transformation of AES to 01001001.
404 views

### Why are in asymmetric cryptography as many keys as people involved needed?

The question: "10 friends wish to establish secure communications between themselves using asymmetric-key cryptography. How many keys need to be known by each user?" was posed by my teacher. He says ...
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### How to show that Affine crypto have a valid decryption

I just need to know how to attack a question I have in my textbook this is like: Let $E_1 (x) \equiv 17x + 7 \pmod{28}$ and $E_2(x) \equiv 23x + 11 \pmod{28}$ be encryption functions for two ...
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### Will CT (Certificate Transparency) override the use of CAA and/or DANE/TLSA records?

I'd want to know if some of these competing technologies has more chance to survive. It seems they are thought to solve a similar problem by different manners and I'd want to stick to the most ...
38 views

### Generate private key from public key RSA

I am doing a tutorial where my lecturer (PhD) gave me an optional question to do relating to RSA. He said: write a python function that takes as input the server’s public key and then uses that to ...
28 views

### What are the advantages of runtime defenses vs. compile-time defenses against buffer overflow? [on hold]

What are the advantages of runtime defenses v compile-time defenses against buffer overflow attacks?
48 views

### Text encryption algorithms that can be used and are secure

what text encryption algorithms are being used nowadays that are secure? Obviously I am not interested in DES or 3-DES that google shows me and which can break...
55 views

### What is a multi-target attack on block ciphers?

What exactly is a multi-target attack on a block cipher? How does the attack work? How can it be avoided?
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### Zero knowledge proof that ElGamal ciphertext encrypts the opening of Pedersen commitment

Given ElGamal ciphertext for a message $m$ with a random $r$ as $(c_1,c_2) \gets (g^r, g^my^r)$ for a public key $y$, and a Pedersen commitment $C \gets g^xh^r$, I have been able to create a proof ...
239 views

### Is length extension attack considered as collision?

I came across a few articles about length extension attacks on cryptographic hash functions. I was very surprised to read that SHA-256 and SHA-512 are prone to length extension attacks. This seems ...
63 views

### Choice of finite fields for use in elliptic curves

this is maybe a basic question but I'm trying to better understand elliptic curve cryptography at a fundamental level. I understand that a finite field is required in order to define a boundary for ...
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### one hash for two (or more) different input values

I build an application that has to interact with legacy applications (outside zone of control). There are shared entities (medicines, pharma companies) between my and legacy apps. Each legacy app ...
11 views

### Is there any existing Threshold Authorization Token?

By Threshold Authorization Token I mean a token (similar to a JWT) that is produced by a (t,n)-threshold scheme. I'm trying to gather background on the subject, but it's hard to find anything, if ...
35 views

### RSA decrypt message with low public exponent (n = 187, e = 3 and C = 185)

n = 187 e = 3 C = 185 How to decrypt message? I know there is some way using cryptogram exponentiation. Can you give me a hint?
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### Zero knowledge proof with accumulators

I am working on a proof of concept on cryptographic accumulators. delta: The current size of the tails file in the accumulator. witness: The current value of the accumulator when the entry of your ...
40 views

### Where are labels of a Labeled data used in homomorphic message authenticator stored?

In a fully homomorphic message authenticator, Alice can authenticate some large data $D$ using her secret key $s$k. She chooses a label $\tau$ for it, and the authentication algorithm authenticates ...
18 views

### Change windows live mail password?? Issue [on hold]

Gentlepersons, I am using Windows Live Mail as my e-mail program at the moment. I've been using it without a question for several years ... until recently. I've had problems with changing my e-mail ...
46 views

### Do garbled circuits run in constant time?

It seems like garbled circuits should not be input dependent, and hence should always run in constant time. Just wanted to clarify if this is true.
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### Why do we use prime numbers apart from hard factorization?

Why are prime numbers important in cryptographic constructs? I am not interested in RSA examples where factorization is the hard problem itself, that makes sense. However wherever I go I encounter ...
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### What does the server do on receipt of a one-time-password?

I'm trying to understand this question and I do not understand part of it. I have part of figured out, part of it not. Considering the hash function h(i) = (i + 5) mod 7, used in an implementation ...
48 views

### Is a keyed MAC sufficient for integrity protection?

I'm working with the above figure which shows a challenge-response protocol. ...
29 views

### NTRU Bilateral Key Exchange

With the NTRU scheme, is the key exchange only done by encrypting a symmetric key with the recipients public key (+ authentication) or can something similar to DH/ECDH be done, where public ...
48 views

### If there is an algorithm A can calculate the modular square root of input n, How to use it to get prime factors?

Suppose you are given an algorithm $A$ which takes $y \in \{0, 1, \ldots , N − 1\}$ as input, and outputs $x \in \{0,1,\ldots,N − 1\}$ such that $x^2 \equiv y \pmod{N}$. Design an efficient, ...
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### Why does curve25519 use a cofactor of 8?

This cofactor (as I understand it) effectively discards valid points that satisfy the curve equation over the finite field. Why would one wish to reduce the number of possible private keys, it seems ...
43 views

### Is there a point in storing hash or plaintext in the last column of Rainbow Tables

As I read up on rainbow tables, I found that most sources suggest storing a plaintext - the result of Rk(hk) - in the last column, while others just store the hash hk, basically stopping one step ...
23 views

### Key exchange and authentication using libhydrogen

I have been able to exchange session keys on two devices using Libhydrogen's Key exchange using the N variant method. I also want to authenticate both devices to have some protection against the Man ...
106 views