0
votes
1answer
61 views

Blowfish ECB mode: Tools for known-plaintext attack?

I'm currently dealing with multiple blowfish-encrypted files that share the same key. All are encrypted using ECB mode judging from their appearance. I don't know what the key is but I know 64 byte ...
1
vote
1answer
49 views

RSA-blind signatures vs. DSA-blind signatures

I see that the RSA blind signature scheme tends to be implemented more often than others, e.g., DSA blind signatures. Isn't the RSA blind signature scheme a 'lesser' scheme, if you may, compared to ...
0
votes
0answers
51 views

Recovering a constant salt for MD5 [duplicate]

I have STRING and MD5(STRING+SALT) for any infinitely many STRING's. Is their any way that I can recover the SALT itself? (SALT is constant) I actually know SALT, but this is an intellectual exercise. ...
0
votes
1answer
79 views

Probability of factoring keys as a function of bit length

kinda new here, I had a question pertaining to someone being able to factor one's RSA keys through the GCD. Anyways the question goes that there are two people: A and B. A makes his/her private key as ...
0
votes
1answer
89 views

What are the potential (major) flaws in this security scheme?

It’s been a few years since I read anything involving crypto. I’ve come across this scheme and I wonder how secure it is: Alice generates an RSA keypair (we assume Alice is using proper random ...
1
vote
1answer
50 views

Reduced message expansion in NTRU

In the original NTRU proposal from 1998, it says on page 16: It may be worth mentioning, though, that there is a simple. masking technique that can be used to significantly reduce message ...
1
vote
0answers
55 views

How does Schnorr signature actually work?

I'm trying to get a grip on how Schnorr signature works. Suppose Alice sends Trent a tuple $(P, M)$, which contains a payload and a message to be signed by him. She then passes the certificate to Bob ...
3
votes
1answer
127 views

Decrypt all RSA ciphertexts if you can break 1% of them

I was given a cryptography question during an interview the other day. Imagine you are given an efficient algorithm which for a given RSA public key (n,e) is able to decrypt 1% of the messages ...
1
vote
0answers
65 views

Crack RSA with imaginary algorithm [duplicate]

I was given a cryptography question during an interview the other day and I couldn't come up with a valid answer. Imagine you are given an efficient algorithm which for a given RSA public key (n,e) is ...
2
votes
1answer
153 views

2048-bit RSA Decryption

Im in need of help with this study question. I heard that there was some relation between small a's and b's and being able to do a trick but I cant find where I read it in my book. Could someone help ...
1
vote
1answer
86 views

Timelock puzzle improvment

I came across this question with this answer about a cryptographic timelock-puzzle that needs approximately 30 years to be solved. There is also an explanation with source code for that puzzle ...
3
votes
3answers
136 views

Statistical properties of hash functions when calculating modulo

When using SHA-1 to hash an input, the result is a pseudo-random number in the numeric ID space $\{0\dots2^{160}-1\}$. Do I loose any statistical property in the result if I use modulo to restrict the ...
4
votes
1answer
138 views

Are post-quantum cryptographic ciphers *also* secure if the P=NP conjecture holds true?

First of all, I only understand the P versus NP debate on a rather shallow level as I am not a computer scientist. So perhaps the answer to the question is straightforward but if not, I would be ...
1
vote
1answer
77 views

CBC-R when IV unknown

I've read the CBC-R description from Rizzo & Duong but am having trouble understanding the sequence of steps that would be taken when the IV is unknown and is not included with the ciphertext. ...
2
votes
1answer
59 views

Is xgcd faster than Fermat for calculating $d$ in RSA?

I want to calculate $d$ from $e$ when generating RSA keys. What is faster? Calculating $\operatorname{xgcd}(e,p)$ and $\operatorname{xgcd}(e,q)$ and CRT. Or calculating $e^{p-2}\bmod p$ and ...
0
votes
2answers
130 views

Voting system validation

I'm developing an application to run elections. A voting system. I would like to give the ability to the voters to check later if their vote were correct computed/casted. assumptions: each user has ...
-3
votes
1answer
32 views

cipher inside and image [closed]

I have a short cipher of (33) characters , which is only ascii characters. From this information. Is it possible to guess what kind of encryption was that?
0
votes
1answer
66 views

rotational cryptanalysis on modulo multiplication?

I saw the paper 'Rotational Cryptanalysis of ARX', it is effective against design primitives using XOR, addition, and rotation. http://www.iacr.org/archive/fse2010/61470339/61470339.pdf However ...
0
votes
1answer
39 views

Explanation of the Fiat-Shamir heuristic

The Wikipedia page on the topic (http://en.wikipedia.org/wiki/Fiat%E2%80%93Shamir_heuristic) is completely useless as it only explains what it is and not how it works. I looked at the original paper ...
0
votes
0answers
40 views

PRG variant as a commitment scheme

I would like to use a PRG in order to achieve the commitment properties (i.e. Hiding and Binding), however, if we look at a general PRG we cannot state that it has the Binding property. First I show ...
1
vote
0answers
50 views

RSA or Paillier is good? [closed]

I want to implement file storage in cloud using homomorphic encryption. I want to use paillier encryption. Can you suggest the drawback of RSA to store and retrieving the files. Then only i can use ...
0
votes
1answer
76 views

Storing AES encrypted RSA private keys on a server

I'm thinking about creating an encrypted messaging web application where users create RSA key pairs, they store the public key on the server for others to see and also store an AES encrypted private ...
0
votes
0answers
28 views

Linear Code - Hamming - Finding nearest vector

I am studying for my finals and I have a review problem I can't solve. For purpose of doing this problem by myself, I'll leave out certain details. So this is concerning Hamming distance I suppose. ...
0
votes
0answers
47 views

CAST-256 (CAST6) versions or S-Boxes

Are there different versions of CAST-256 - also known as CAST6 - available? Are there different S-Boxes available for CAST-256? If there are different versions or S-Boxes what identifier should I use ...
2
votes
3answers
87 views

Difference between Symmetric and Asymmetric. Is this answer correct, based on a written test?

I asked the following question on a final exam: Symmetric Ciphers (e.g. AES, DES, Blowfish) use up to 256 bit on the best case, which are considered strong against brute-force attacks. On ...
0
votes
0answers
58 views

processing time for multiplication and exponentiation in pairing base cryptography

I'm using the Boneh-Boyen-Shacham signature scheme and want to estimate complexity in my scheme. As reported in "Scott M., Efficient Implementation of Cryptographic pairings", if we set parameters ...
0
votes
2answers
65 views

Proving the semantic security of the One Time pad

Currently hearing a lecture on cryptography, and the professor gave us the definition of semantic security, which is roughly the following (formally not quite complete, but you get the idea): ...
-1
votes
0answers
32 views

How to convert a bit string into a point in an elliptic curve? And when to say that a hash function is a random oracle? [closed]

I read that hash function $H_1\colon\;\{0,1\}^\ast\to G_1$ that map bit string into points in elliptic curve but I don't understand how? And another hash function used $H_2\colon\;G_2\to\{0,1\}^{\log ...
4
votes
1answer
89 views

Looking For Additively Homomorphic Encryption

I have a construction that requires as primitive an Additively Homomorphic Encryption scheme that does not rely on hidden group order, meaning I can't use Paillier. I now have two different ...
7
votes
2answers
304 views

Streaming API to authenticated encryption

In regards to NaCl, I asked DJB he had any intent to add a streaming API to an authenticated cipher. His response was obvious in retrospect, that one should never release a decrypted plaintext before ...
0
votes
1answer
65 views

Polynomial Modulus

So I am studying for finals and I came across this problem and I am completely stuck. I would really appreciate someone to clarify on the steps to take to solve these problems. Let $f(x) = x^4 + x^3 ...
0
votes
1answer
27 views

Cocks IBE Scheme: why is -a a quadratic residue mod n?

In the Cocks IBE scheme it is required for the hash function, that the Jacobi symbol of its output and the universally available moduls $n = p*q$ is $+1$, so: $\Big(\frac{H(ID)}{n}\Big) = ...
-1
votes
1answer
63 views

what is the benefit of lcm in cryptography? [closed]

what is the benefit of lcm in cryptography? and what is the effect of lcm on public key? note * lcm = Least common multiple thanks
3
votes
1answer
253 views

Generating a valid signature on El-Gamal without knowing the private key

Suppose we are given $p$, the large prime, $g$ which is the primitive root for $p$, $b$ which is calculated as $b=g^x$ mod $p$ where $x$ is the private key and $0<x<p-1$. Also suppose we know ...
0
votes
0answers
45 views

Are there any proofs of the SHA1 compression function's (second-)preimage resistance?

Why is SHA1 preimage-resistant? The best reference that I can find is Rogaway & Shrimpton's 2009 paper, and I'll use their definitions. The kind of preimage resistance that is wanted is aPre. ...
1
vote
0answers
74 views

Interactive assumptions not falsifiable?

Can someone explain why an interactive assumption is not falsifiable? Maybe I'm misunderstanding what the statement means, but isn't even a non-interactive assumption interactive, but just with a zero ...
1
vote
1answer
66 views

Fermats Little Theorem, primitive root [closed]

So I am studying for finals and I am not able to solve the problem: Let $ p = 3 * 2^{11484018}- 1 $ be a prime with 3457035 digits. Find a positive integer $x$ so that $2^x\equiv 3\pmod p$ Any ...
1
vote
1answer
128 views

How can I map arbitrary group elements to unique integers without using Hash functions?

Let's say, I have a group $G$ of large prime order $p$. A set $S$ consists of $n$ random elements chosen from $G$. Without using a collision resistant hash function $H$, how can I map elements of $G$ ...
1
vote
1answer
61 views

Does it necessary the public key is prime number in RSA algorithm?

I read some books talk about RSA cryptography but I did not understand something when choosing a public key $e$ Sometimes the condition is $1<e<$$\phi(n)$ Where $\phi(n) = p-1 * q-1$ also ...
10
votes
5answers
1k views

Why should I make my cipher public?

As I understand it, the less people know about the internals of my protocol or cipher, the more secure the protocol is. However Kerckhoffs's principle states that A cryptosystem should be secure ...
0
votes
1answer
41 views

Is a strong block cipher usable as a strong sponge function?

From the literature, it looks like the security proofs of sponge functions depend on how well they approximate a random permutation, Since a block cipher also ideally behaves like a random permutation ...
4
votes
2answers
153 views

Hamiltonicity proof of knowledge

I'm learning the POK notion and definitions and as a self exercise I wante to prove the statement that the Hamiltonicity protocol is a POK system with knowledge error $1/2$. So the question will be ...
1
vote
1answer
30 views

Question about Delerablée's Identity-based Broadcast Encryption

I'm reading “Identity-Based Broadcast Encryption with Constant Size Ciphertexts and Private Keys” by Cécile Delerablée. In Page 207, encryption process needs $\gamma$ which is part of master key. ...
0
votes
0answers
33 views

Active Sbox count in PRESENT Cipher [closed]

Can any one please tell me how to calculate active Sbox directly or is there any c code for it?
0
votes
0answers
39 views

Primality of number 1 [migrated]

Is number 1 prime as per the definition of prime numbers? Because as per the definition for being prime it should be divided only by 1 and number itself.
0
votes
0answers
43 views

Polynomial Inversion over Galois Field

Hello guys I am looking to calculate the Inverse of a given polynomial in Galois field I have found the little Fermat's algorithm and the Itoh-Tsujii I am getting a bit confused with both algorithm ...
0
votes
3answers
308 views

What block cipher is used for CBC-MAC?

What block cipher is used for CBC-MAC? DES, AES, 3DES? Or it doesn't matter?
1
vote
1answer
119 views

rsa public and private keys

I have a question about RSA key generation. This is a simple RSA algorithm: Choose p = 3 and q = 11 Compute n = p * q = 3 * 11 = 33 Compute ?(n) = (p - 1) * (q - 1) = 2 * 10 = 20 Choose e such that ...
2
votes
2answers
631 views

Can a salt for a password hash be public?

For my understanding salts in password hashes are used to prevent the precomputation of $plaintext \to hashvalues$ (rainbow tables). I know from different threads, it is not necessary to keep the ...
0
votes
1answer
43 views

Is there (this) a case in which salting is dispensable?

tl;dr this is not a duplicate of "what is a salt/why use salt?" question. Instead it is specificly asking when salt may not be necessary for hashing securly? (i.e. when the data being hashed is ...

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