1
vote
1answer
40 views

Is the “Hash Tree” described in this paper the same as a Merkle Hash Tree?

I'm implementing an algorithm from a paper, and part of it calls for using a "hash tree". Since I'd never heard of that data structure I looked it up on Wikipedia. It turns out that the name hash tree ...
4
votes
0answers
41 views

Do we still need HMAC now that SHA3 is here? [duplicate]

In Another look at HMAC from Koblitz and Menezes, they state that HMAC came along because doing h(secret || message) was vulnerable to length extension attacks. But as far as I know, these kind of ...
1
vote
1answer
37 views

Prove that a function is PRF

Let $F : K×K \rightarrow \{0,1\}^{128}$ be $PRF$ function. Is $F'$ $PRF$ ? $ F'(x) = \begin{cases} 0^{128} & \quad \text{if } x = 0\\ F_k(x) & \quad otherwise \end{cases} ...
1
vote
0answers
18 views

How to calculate how many trials I need to guess the plain text if a simple P-Box is used to make the cipher text

If I have 64 bit as input for a straight box that use a transposition process to encipher the plain text and the given 64 bits contains 60 bits as (1s), then how many trial I should do?
3
votes
0answers
57 views

Simultaneous 2 way exchange without trusted third party

Stakeholders: Alice - has a message, M containing a secret, SA that Bob wants, where H(SA) is a hash which may be used by Bob to redeem some Bitcoin time-locked transaction sent previously by Alice. ...
-2
votes
1answer
57 views

Carmichael's function in Cryptography

The Carmichael's function says that for $a\in \mathbb{Z}_n^*$, if $gcd(a,n)=1$, then \begin{equation} a^{\lambda(n)} \equiv 1 \;(mod\; n). \end{equation} My aim is to find $a$ if factorization of $n$ ...
0
votes
1answer
40 views

What is a simple information authentication protocol for constrained devices?

Background: I have an application where devices will poll information from some source on the network. These devices are very basic and have modest processing and memory capabilities. Hashing (and ...
3
votes
0answers
62 views

How to select corresponding ciphertext in anonymous Identity-based broadcast encryption

In identity-based broadcast encryption, suppose the broadcast ciphertext $(r_1,r_2,\dots,r_i,U,W,V)$ is sent to the receiver. It does not describe which user corresponds to which ciphertext part. User ...
0
votes
2answers
63 views

Diffie Hellman Exchange Confusion [closed]

I am working on this question and I am wondering I have figured out the secret key, but my problem is I don't know how to use the secret key to decrypt the ciphertext. Thanks for the help!
-2
votes
1answer
81 views

How many hashes one needs in order to reverse engineer hash function?

If I know the pattern of a hash string, particularly dllldlll or llldllld (d=digit, l=low case letter), is it possible to reverse engineer the hash function? If so, how many hashes ones needs to do so,...
0
votes
0answers
33 views

Security or not in Key distribution

For example, There are 3 clients. I want to deliver specific value $x$ to all clients. $x\leftarrow {0,1,2,...,q-1}$ where q is a large prime number. By using function $f(x)=x*y_{i}*z_{i}$ where i=...
3
votes
1answer
36 views

Is there a way to turn a PGP key into its semi-prime counterpart?

From my understanding of PGP keys they use the RSA algorithms to encrypt/decrypt messages. So, I know that the RSA algorithms use a semi-prime number to encrypt/decrypt messages. So, what I was ...
1
vote
0answers
59 views

Software Security Impossible in Non-Trusted Hardware?

Fundamentally it is impossible to protect software if you can't trust the execution platform (e.g. using a TPM), so what is the point of software security then? With vendors claim that their white-...
0
votes
2answers
2k views

If I can crack the AES, how do I crack the wifi [closed]

I am a student major in math. My teacher said that AES (Advanced Encryption Standard) has many applications. For example, the WPA2 in wifi. Then he taught the theory of the AES and never says how to ...
4
votes
2answers
96 views

Recover elliptic curve order from ECDSA signatures

I need the elliptic curve order to recover the private key from two signed messages with ECDSA. What I have: two signatures signed by the private-key I want to get the messages that have been ...
1
vote
0answers
47 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
35 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
75 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
36 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
105 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
35 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
46 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
208 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
84 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
697 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
26 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
65 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
38 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
269 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
39 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 ...

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