0
votes
0answers
24 views

How to determine which key derivation function used for password?

Suppose an attacker collected a password hash file. After performing rainbow tables/dictionary attacks they choose brute force attacks. So they try guessing as many passwords as they can by running ...
0
votes
0answers
19 views

Generate CA with aes256 passphrase protected DSA key

I want to create my own Certificate Authority with an DSA key. I figured out to create it with: ...
0
votes
1answer
64 views

Bae64 with shuffled alphabet

I have a base64 'cipher' text, I know that in clear text is a hidden xml document (I do not know nothing about its structure), but the base64 aplhabet was somehow shuffled. Is there any smart way, how ...
0
votes
1answer
53 views

Looking for a secure PRNG that I can implement in hardware

I'm trying to implement a (sort of) simple PRNG in hardware for fun. My idea would be to allow a user to enter a key using a keypad (or some dip switch settings that can be set and hidden) and to ...
0
votes
0answers
72 views

How do I find a random BigInteger smaller than another random BigInteger? [migrated]

How do I Select a random element α ∈ Z∗p? P is a random 1024 bit prime BigInteger. Here is how I find BigInteger p: ...
1
vote
1answer
89 views

Is it safe to AES-CBC and AES-CMAC both using the same key?

There is a very similar question (Using a derived key for CMAC) but it doesn't quite answer this one (at least for me it does not). I have a situation where I need to transfer some data. My data has ...
1
vote
1answer
65 views

Why do we have fixed output length in the algorithm SHA1

Why do we have fixed output length in the algorithm SHA1 . is there any explanation about that
1
vote
1answer
50 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 ...
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 ...
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. ...
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 ...
3
votes
1answer
129 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
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 ...
0
votes
1answer
91 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 ...
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 ...
1
vote
2answers
83 views

Group description in pairing based cryptography

Suppose we have a public key encryption scheme, in which public parameter contains $(p, G, G_t, e, g)$, where $p$ is prime number, $G$ is a (cyclic) group of prime order, $e:G \times G \mapsto G_t$. ...
-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?
4
votes
1answer
57 views

At what point does passphrase strength match the strength of the cipher?

Let's say that I have an ordinary hard drive encrypted with VeraCrypt 1.0e full disk encryption and implementing: -AES -RIPEMD-160 Hash Algorithm Now let's say that for an arbitrary machine, the ...
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
51 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
0answers
29 views

S-Boxes and SP-Network

I work on an exercise and I have to study functions as : $ f : \mathbb{F}_q \rightarrow \mathbb{F}_q$ with $q = 2^n$ which can define a S-Box for SP-Networks. There is a question that I can't answer ...
2
votes
1answer
154 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 ...
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
1answer
68 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
80 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 ...
2
votes
3answers
90 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
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): ...
3
votes
3answers
141 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 ...
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
28 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
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
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 ...
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 ...
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. ...
0
votes
1answer
40 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 ...
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
62 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 ...
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 ...
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. ...
4
votes
1answer
91 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 ...
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
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
44 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 ...
1
vote
1answer
88 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 ...
1
vote
1answer
47 views

MD-compliant hashes don't really accept arbitary length input, do they?

When people talk about hash functions, they usually say that they accept arbitrary-length input, but if you actually look at the padding (eg MD-strengthening padding), you see it's like ...
-1
votes
1answer
39 views

HMAC ipad and opad choice

It is written in the HMAC paper that the $ipad=0x36$ and $opad=0x5c$ were chosen such that it maximize the Hamming-Distance of the part of the key used in the inner and outer part of the HMAC process. ...
1
vote
0answers
48 views

Asymmetric encryptions' computational complexity [duplicate]

I need to know the computational complexity of the public key encryption (e.g. Paillier), please. (i.e.Paillier in his paper mentions that the computational complexity of most of public key ...
-2
votes
0answers
50 views

CCA security in double encryption [duplicate]

my friend and I are trying to reach out a convenient security solution for CCA when we encrypt the message m two times, first for m to get c and then for c to get C(so it is one inside other). I have ...
-1
votes
0answers
64 views

Why is device ownership useful? [migrated]

There are two scenarios that I have saw device ownership. In TPM, there is an ownership establishment procedure. When we purchase a new cell phone, the SIM card activation also has some ownership ...

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