1
vote
0answers
46 views

Safe MAC proof check

Let $(Mac, Vrfy)$ be a safe defined $MAC$ over $(K,M,T)$ where $ M = \{0,1\}^n$ and $T = \{0,1\}^{128}$. Is the following $MAC$ safe? Show your proof. $Mac'(k,m) = Mac(k, m)$ $Vrfy'(k,m,t) = \{Vrfy(...
1
vote
0answers
22 views

What do Quantum computers mean for security? [closed]

I know that Quantum computers can speed up brute forcing a key by a ton, but how much? And what does that mean for privacy? Does this just mean that the FBI's side of that court case has won until the ...
1
vote
1answer
34 views

Affine decryption

A message has been converted to ASCII and then encrypted with the formula: $$ax+b \equiv n \pmod {215475}$$ The encrypted message is: ...
1
vote
1answer
74 views

Security of a MAC

Let $(Mac, Vrfy)$ be a safe defined $MAC$ over $(K,M,T)$ where $ M = \{0,1\}^n$ and $T = \{0,1\}^{128}$. Is the following $MAC$ safe? Show your proof. $Mac'(k,m) = Mac(k, m ⊕ m)$ $Vrfy'(k,m,t) = ...
0
votes
0answers
15 views

Self-signed certificate becomes invalid after some time [migrated]

I have a web site hosted on IIS webserver. I've created a self-signed certificate for the web site and installed on a client machine. When I install the certificate to a client machine, I can ...
4
votes
1answer
85 views

How to prove a function is pseudorandom function?

I am currently enrolled in a cryptography course, which uses the book by Katz and Lindell. I am using a function having $F_{k}$ = $A_{k}(B_{k}(r,m),r)$, the random number is generated using the ...
-2
votes
0answers
35 views

Secret Key Encryption in identity based encryption

If we assume $x$ be secret value $x\leftarrow{0,1,2,....,q-1}$ where q is a prime number Instead of using public key encryption schemes, using a function such as $f(x)=x*y/z$ to conceal $x$ value ...
5
votes
1answer
103 views

Encrypted firmware

I have seen many papers on "encrypted firmware" (for example, firmware on Apple Watch like devices) . Can you tell me how it works? Is there a stub in the firmware which is not encrypted and can ...
1
vote
1answer
34 views

How does BB84 fare against an attacker who can entangle qubits?

Consider the following attack on the BB84 quantum key exchange protocol (as far as I can tell, it should work similarly for E91): After Alice sends her key bits encoded in qubits with randomly chosen ...
13
votes
2answers
1k views

Do key collisions for symmetric ciphers exist?

I'm not sure if I'm calling the thing (key collisions) correctly, and that's probably why I couldn't find any information about it on Google. Still, my question is as follows. Note that I don't work ...
1
vote
0answers
11 views

Can using a cascade encryption decrease security? [duplicate]

When using cascade encryption, can you actully decrease the security, for example if you do something wrong, or is it only depend on which algorithm or mode of encryption you use?
1
vote
0answers
10 views

Why the light contrast of a set $\mathcal{E}$ of VCRG produced by an encryption scheme for a binary image B is defined as follows

In the paper “Image encryption by multiple random grids”, Shyong Jian Shyu, 42(7):1582-1596,· July 2009, the light contrast of a set $\mathcal{E}$ of VCRG produced by an encryption scheme for a binary ...
4
votes
1answer
36 views

Do the limitations of PRNGs apply to CSPRNGs when shuffling a list?

Suppose, as an example, we want to use the Fisher-Yates algorithm along with a pseudorandom number generator to shuffle a deck of cards. We know that there are limitations with respect to the internal ...
0
votes
0answers
9 views

Restrictions about combination of participant in a (4,4) visual cryptographic scheme

Let $\Gamma_0 =\{\{1,2,3\},\{1,2,4\},\{1,3,5\},\{1,4,5\}\}$. Well, we get basis matrices easily. But I don't understand, why is the set of participants $\{2,3,4\}$ is forbidden? How to say such thing ...
0
votes
1answer
58 views

Can you tell me how to create a cipher please? just a little simple one [closed]

I don't how to make a cipher text at all, can you help me?
4
votes
1answer
45 views

Ideal way to profile/performance-measure cipher implementations

I have implemented a bit-sliced version of two ciphers (Gibbon-120 and Hanuman-120, both part of the Primates family of ciphers: http://primates.ae/wp-content/uploads/primatesv1.02.pdf ) I now want ...
1
vote
4answers
207 views

Can you use a hash as a password?

There are several methods of making a strong password, making it longer is one of them. now we also have hashing algorithms which have outputs of 512, so i wonder, would it be safe to basiclly use a ...
0
votes
0answers
55 views

Why can't current quantum computers break RSA? [duplicate]

We have quantum computers and we also have Shor's algorithm. So: Why isn't RSA cracked yet? What are the current quantum computers lacking?
3
votes
1answer
82 views

RSA Digital Signature vs Elgamal Digital Signature

What are the advantages of RSA signatures against ElGamal signatures? Is there a situation in which it would be better e.g. to use RSA signatures?
14
votes
2answers
690 views

Password entropy much lower than entropy of encryption keys. Why is this acceptable?

When talking symmetric encryption, a 56 bit key is known to be so weak. If you use it for your encryption, you are considered a goner. When talking passwords however, the standard these days is ...
20
votes
6answers
4k views

Did a certain cryptography method get abandoned due to security flaws in the past?

I am researching how quantum computers affect current encryption methods (RSA and more). However, I remember learning in a course that there used to be a particular encryption method which was ...
2
votes
1answer
57 views

Are transposition ciphers insecure?

Given plaintext: P[i], i = 1..N Given stream of cryptographic numbers S[i, j], i = 1..N, S[i, j] in [1, j] generated by RC5 for example We encrypt using Fisher-Yates shuffle algorithm: ...
4
votes
1answer
37 views

If A and B are co-primes, does Ax mod B (where x, any positive int) gives {0,1,2,…,B-1}?

If $A$ and $B$ are co-primes (i.e. $\gcd(A,B)=1$), does $A\cdot x \bmod B$ (where $x\in \mathbb N$) give as result an element of $\{0,1,2,....,B-1\}$ ?
2
votes
0answers
29 views

Boneh/Franklin Identity based encryption with Tate pairing

Boneh/Franklin developed an identity based encryption scheme based on the Weil Pairing. This algorithm has also been standardised in IEEE P1363.3 . I know that this algorithm can also be implemented ...
4
votes
1answer
126 views

Why does choosing the first coprime e greater than half of φ(n) result in the same d (private exponent)

While reading on RSA's algorithm, I attempted a simplified implementation and noticed the following: When choosing the public exponent $e$, if the value chosen is the first coprime after $φ(n)/2$ ...
1
vote
1answer
25 views

What are the correct order of operations for One Time Pad Cipher?

According to Wikipedia the One Time Pad Cipher is unbreakable. On the Wikipedia page it explains how to perform this simple encryption process by hand. For the encryption it adds (+) the message and ...
3
votes
0answers
26 views

What are the practical impacts of Wassenar Arrangement to crypto development?

Wassenar Arrangement limits transport of high-grade crypto hardware/software since decades, if I don't err. What are its practical impacts in that direction? In particular, does it hinder in any sense ...
1
vote
2answers
63 views

How secure is HMAC SHA256

I have a message (UUID) in this form 406a5830-2a6a-11e6-bdf4-0800200c9a66. I also use a secret key for example ...
1
vote
0answers
38 views

I Have An Encrypted Message [closed]

I am a newbie to cryptography and am stuck on decrypting a message. This message was received from a friend and I would like to crack it in order to respond. I have decrypted part of it but am unable ...
6
votes
0answers
37 views

Does a partial preimage attack imply a preimage attack?

Let's assume we have an $n$-bit hash function and a $b$-bit partial preimage attack that is faster than brute force. Does this imply a faster than brute force preimage attack on the whole hash? It ...
3
votes
1answer
76 views

Highest prime factor that is Safe for a particular scheme

My question is how many bits of prime number is secure so that it cannot be factored from very large number? Until today how large prime factor is found in large number? Quantum computing find ...
0
votes
2answers
71 views

Factoring an RSA modulus given high bits of a factor

I have {e,N,C} and part of p; can I get q from this example : ...
16
votes
2answers
263 views

Is it possible for Alice and Bob to both sign a message “simultaneously”?

Let's say that there is a message which is considered valid if signed by both Alice and Bob. Alice could sign the message and then give it to Bob, so that he can sign it and give it back to her. But,...
6
votes
1answer
82 views

How to calculate active s-boxes from branch number?

If MDS in AES has branch number 5 (so 5 active s-boxes in 2 rounds), wouldn't that mean 4 rounds of AES has $5*2=10$ active s-boxes? AES paper says it has 25 ($5^2$?) active s-boxes in 4 rounds. How ...
6
votes
1answer
38 views

Did authentication/signature primitives fall under the Wassenaar Arrangement?

I understand that under the Wassenaar Arrangement, encryption algorithms like AES were considered to be some sort of weapon. The legally allowed effective key sizes in export software were limited to ...
4
votes
1answer
72 views

Enhance security by combining bits of 4 different hashes

Assuming that performances do not matter, is there any real benefit in terms of security (in general) in combine hashes in this way: hash functions: ...
4
votes
1answer
41 views

Key derivation with Curve25519 for data encryption

I'm new when it comes to cryptography so this question might be a little bit stupid: Can I derive a key with Curve25519 from a (let's say) root key and encrypt the file with a secret key algorithm? ...
12
votes
2answers
2k views

What's wrong with XOR encryption with hash and an iterated salt

Suppose you'd use the following algorithm to encrypt a message Let $k$ be the key to encrypt with Let $m$ be the message to encrypt Split $m$ into groups of 512 bytes Given a hash function with ...
6
votes
1answer
300 views

Is it insecure to generate a key with your own public and private DH keys?

Is a secret key generated with its own public and private keys any less secure than a "normal" secret key generated using DH key exchange? Example: ...
1
vote
1answer
25 views

Audio Encryption in Voip SIP [closed]

I have some project encrypion real-time. I want use Voip SIP to implement the stream cipher. What I have done so far : Simple app android Voip SIP https://github.com/android/platform_development/...
3
votes
1answer
36 views

How does this solution guarantee authentication of B and privacy?

The exercise is: What could be changed on the second message " Kya(Kxb(Ra,Ks)) " to guarantee B's authenthicity and also privacy? My teacher's solution was "add a destination" , so it would be ...
8
votes
3answers
255 views

How secure is AES-256, but with an effective key length of 56-bits?

I need to encrypt a few drives using Kaspersky Total Security. I however noted something peculiar, Kaspersky's description of their cipher is: Data will be protected using AES-256 encryption ...
0
votes
1answer
30 views

meaning of Reduce f modulo the order of the base point G

I am trying to perform some math operations related to Elliptic curve cryptography, and came across this sentence: Reduce f modulo the order of the base point G. What does it mean?
3
votes
1answer
52 views

Need help understanding this exercise's solution

We were given this exercise, which asks us to identify the types of keys used on this diagram: The solution was Kxa -> A's private key Kya -> A's public key KxB -> B's private key My question ...
0
votes
1answer
114 views

ECDSA non random k - Retrieve private key [closed]

At the moment I'm playing around with ECDSA. I know that I can retrieve the private key if the same K is used to sign two messages. I tried to use this script: Ruby Script to crack the private key. ...
2
votes
0answers
26 views

Cryptographic Algorithm [closed]

I'd like to find out the cryptographic algorithm which uses only lowercase letters and numbers to encrypt a message, and it has 256 bits (always). For example: fff51ebcad2c44c75d7d5d4c5184b3e4
1
vote
0answers
29 views

Simple Code Salsa20 in java [closed]

i am doing some simple research in cryptography. i need simple salsa20 in java without libr (in 1 class). can some one give me simple code to encryp and decryp plaintext from byte[] in java?
5
votes
1answer
225 views

ECDSA key recovery - floating point values

I'm currently attempting to recover an ECDSA key. I have $m$, $m'$ and signatures $(r, s)$, $(r', s')$, and I know that $k$ is constant, the curve is NIST P-192 and the hash function of the. As such,...
3
votes
1answer
87 views

How to hash a set of elements

Imagine the following senario. We have $n$ participants. Participant $i$ has a set of elements $S_i$ with the elements being in a random order, possibly different for each participant. The ...
2
votes
1answer
55 views

Term for the ratio of ciphertext to plaintext size?

Is there a term that determines the ratio of size of ciphertext $|c|$ and plaintext $|n|$? I vaguely recollect reading it as scale out factor. Is there a better term? Or a popular term for this?

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