0
votes
0answers
4 views

any post-shannon symmetric ciphers?

As far as I understand block ciphers use only simple operations to ensure good enough confusion and diffusion levels. meaning there is no math in it. "breaking a good cipher should require as much ...
2
votes
2answers
83 views

Calculating Polynomial Inverse with extended euclid in java

I'm trying to understand the NTRU-PKCS and therefor I wanted to code a naive Version of it. Now my Problem: I tried to calculate the inverse of a Polynomial with an extended Version of euclids ...
0
votes
1answer
6 views

Why is symmetric lightweight crypto only about block ciphers and not about stream ciphers?

Why is symmetric lightweight cryptography only about block ciphers and not about stream ciphers? AFAIK stream cipher implementations cost at least three times less than block cipher ones?
0
votes
0answers
10 views

Does changing the order of the steps within a round affect the security of AES?

I was trying to understand the internal structure of AES (Advanced Encryption Standard) Standard order of steps within a round: Substitute Bytes Shift Rows Mix Columns Add Round Key Substitute ...
2
votes
0answers
12 views

hash function notations and existing cryptographic hash algorithms

I am implementing Role-based access control by referencing the paper Enforcing Role-Based Access Control for Secure Data Storage in the Cloud. In page 6, they have mentioned to choose hash functions $...
0
votes
0answers
8 views

What does the last chunk of Scrypt means?

When you use scrypt to hash a string, it will generate something like: ...
1
vote
0answers
13 views

In paillier homomorphism how do you substract?

I'm trying to learn homomorphism so the problem may also be in my code (which I will include). I want to compute [a-b] where a is bigger then b. In order to do ...
1
vote
1answer
18 views

“NP-complete” authentication systems

Are there any symmetric authentication systems based on the hardness of an NP-complete problem? I understand that it doesn't really matter, since NP-completeness is about the worst case, and in crypto ...
1
vote
1answer
28 views

Rotating password with PBKDF2

Crypto is hard. Thank you for helping me learn. My encryption scheme currently looks like this: Salt is stored out in the open Secret is the user's password, known only to them EncKey||AuthKey = ...
6
votes
2answers
325 views

We can obtain “absolutely perfect CONFIDENTIALITY” using the one-time pad. Is there such a thing as “absolutely perfect INTEGRITY”?

The OTP (one-time pad) gives us perfect secrecy. This is the very best confidentiality available in this universe. (Although it does require large keys, which is beside the point of this question). ...
3
votes
2answers
45 views

SHA-3 maximal number of zeros (Padding)

What is the maximum number of zeros, which are appended at the input- padding in messages? How large must the message be for this?
-2
votes
1answer
28 views

pseudo-random-function

please, can you help me about this question... Design a blockcipher E : {0, 1}k × {0, 1}128 → {0, 1}128 that is secure (up to a large number of queries) against non-adaptive adversaries, but is ...
6
votes
1answer
214 views

Is it possible to determine or estimate the period for Blum-Micali PRG?

The Blum-Micali is a cryptographically secure pseudorandom number generator. The construction (from wikipedia): Let $p$ be an odd prime, and let $g$ be a primitive root modulo $p$. Let $x_0$ be a ...
-2
votes
0answers
23 views

Signing and hashing a new file detected in a folder

I'd like to sign a file in a folder after detection. I'd also like to save a hash over the file to a text file. Thanks in advance!
1
vote
1answer
37 views

What is the starting point of Hellman's TMTO method?

I understand what is happening and how the endpoint is computed but I'm still a bit unsure of where "SP" (Staring Point) came from. Are the starting points, randomly selected keys from the key-space n?...
2
votes
1answer
128 views

Doubling the block length of a given block cipher

IMHO the main essence of a Feistel cipher of block length $n$ is the working of a non-linear function $F$ that is applied to the two halves of the block of length $n/2$. Now suppose a certain block ...
3
votes
1answer
273 views

Simple digital signature example that one could compute without a computer?

I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms. There is a great question ...
0
votes
1answer
53 views

What is proper size of window Using RSA Window method?

I want to Use Window method for RSA modular Exponentiation. because of SCA. But I don`t know what is proper window size.
0
votes
1answer
15 views

In Paillier homomorphism, how do you deal with bit length? [on hold]

I'm trying to figure out homomorphic encryption and would like to multiply two paillier encrypted numbers. Like so: [a].[b]=[a+b] To try this I got this Paillier.java and tried the following: <...
1
vote
0answers
29 views

Feasible attacks on ECRSA cryptosystem

In ECRSA cryptosystem, I want to know the feasible attacks. For illustrations we have two prime $p$ and $q$ such that $p \equiv 2 \pmod 3$, $q \equiv 2 \pmod 3$ and generate key pair as follows: $$n = ...
5
votes
1answer
95 views

How can I instantiate a generalized hash function?

I've come across a bunch of "strange" hash function notations, such as the following ones and now I don't know how to choose / instantiate them. Can you please explain me what this notation means and ...
1
vote
0answers
35 views

Build a hash function that returns a digest in $\mathbb{Z}_{N}^{\ast}$

I want to know if there is a way to build a Hash Function in a such way? $\mathcal{H}:{\left\{ {0,1} \right\}^*} \to \mathbb{Z}_{N}^{\ast}$, $N=pq$ and where $p,q$ are primes.
1
vote
0answers
21 views

Hash function notations and their corresponding existing cryptographic hash algorithm

I am implementing Role-based access control by referencing the paper Enforcing Role-Based Access Control for Secure Data Storage in the Cloud. In page 6, they have mentioned to choose hash functions $...
1
vote
1answer
43 views

Does revealing shares of the result reveals shares of the inputs?

Suppose Alive and Bob have shares of two polynomials $P,Q$, say, Alice knows $P_A,Q_A$, Bob knows $P_B,Q_B$ s.t. $P=P_A+P_B$ and $Q=Q_A+Q_B$. They perform some operation $f$ over the shared values, to ...
0
votes
0answers
20 views

elliptic curve and embedding degree

I am new in ECC. I am confused what the embedding degree in elliptic curve represents and what is the impact of its values on the curve and security ( small values or large values? What does the ...
1
vote
1answer
45 views

how to prove sequence y uphold golomb's third axiom

given $\{ x_k \}$ is a m-seq of order $n$, we define $\{ y_k \}$ to be a $m$ digits number: $$ y_i=x_ix_{i+1}...x_{i+m-1} $$ for every integer $n \ge m \ge 1$ how can I show that $\{ y_k \}$ upholds ...
2
votes
1answer
43 views

How is a hash function that implements random oracle model collision resistance?

ROM is considered as collision resistance. Does ROM assume there is an infinite set of output, or assume the output set is always larger than the input set? Because by the pigeonhole principle, ROM is ...
3
votes
2answers
3k views

How to find generator $g$ in a cyclic group?

As generator $g$ is used in DH how do you find a combination of prime $p$ and $g$? eg: if we choose $p=23$ and its generator is $7$ (given in the book) how do we find the generator?
2
votes
2answers
592 views

How do RSA and ElGamal key sizes compare?

I have a rather silly question regarding the comparison of RSA with ElGamal over integers. If you want to compare their performance in the same level of security, does the modulus of both of them need ...
1
vote
1answer
153 views

Prime factorization of 700 decimal digits number

I'm a newbie to encryption. If I create a number 'n' as a product of two prime numbers 'p' and 'q' with the following specifications: 'p' is a fully random prime with 300 decimal digits in length. 'q'...
-1
votes
0answers
33 views

A5/2 Ciphertext Only Attack

I've studied that A5/2 could be attacked with cipher-text only, using the Error Correction Code, in order to retrieve the session key. Here's an article I tried to read about it (section 4). (however ...
13
votes
2answers
571 views

How dead is braid based cryptography

Braid groups has drawn the attention of cryptographers for a few years, as a promising platform for post-quantum cryptographic protocols. The security of the proposed schemes mostly relied on ...
2
votes
1answer
81 views

Forgery attack against Textbook RSA with simple redundancy

I know how to forge vanilla Textbook RSA message signatures (easy). I've learnt that by adding a good redundancy to the message, it cannot be forged anymore. How can one add redundancy so that the ...
0
votes
1answer
9 views

Fix timestamp of self signature on PGP public key [on hold]

I accidentally changed configuration of my pgp key while my system didn't have the correct clock. And I uploaded my key to key servers. Now every time I try to download my key from key servers or even ...
0
votes
1answer
29 views

Getting the same two hash values for carved files I found

I am doing an independent study class for computer forensics, I have to carve the images I've been given. After using scalpel I get a .wav file and .asf file both files play the same songs, and they ...
4
votes
1answer
39 views

How does the key size in supersingular isogeny schemes relate to their security level?

I'm looking at the De Feo, Jao, and Plût 2014 paper: Towards quantum-resistant cryptosystems from supersingular elliptic curve isogenies. My understanding of section 3.2 Key Exchange, is that Alice'...
2
votes
0answers
19 views

What is bounded-retrieval model?

What is bounded-retrieval model in cryptography? How is it related (or apply) to leakage-resilient cryptography?
1
vote
2answers
130 views

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
2
votes
1answer
23 views

Attacks from releasing decrypted CCM payload before verifying tag

CCM specifies (Section 1.7) that no plaintext data should be released before the MAC is verified. Why is this recommendation given and what attacks are possible against CCM if data is treated like a ...
4
votes
2answers
277 views

PGP String-to-Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
4
votes
2answers
455 views

Feistel-Network - why wire crossing?

In Feistel-Network, there would be a wire-crossing at the end (for the next round). Which insufficiency would occur, if the wire crossing would be omitted?
3
votes
2answers
419 views

Any real world implementation using message recovery?

During my master thesis I came across RSA-PSS-R which is in my opinion a quite elegant way of saving bandwidth and space using digital signature. But I didn't find any information about any real world ...
6
votes
1answer
1k views

Description of signatures with message recovery (as in ISO/IEC 9796-2 and EMV Signatures)

I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the ...
3
votes
0answers
37 views

Attacking Scrypt Under Access Pattern Leakage

Could cache-timing channels (such as exist for certain block ciphers) somehow be made use of in order to extract memory-access pattern information if both the attacker and user are NOT in a shared ...
-2
votes
2answers
49 views

How to use modes of operation in DES? [on hold]

How to use modes of operation in block cipher with Data Encryption Standard (DES) ? How the Feistel structure properties are achieved in DES when a mode of operation such as ECB is used?
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
2answers
75 views

Initializing PGP keys by one side

I am using a PGP method to encrypt and decrypt messages shared between users A and B. Upon the start of a message exchange is the initialization of the public and secret keys by both Users. Lets say ...
-2
votes
1answer
36 views

How do I decipher a text using a repeating one-time pad?

I have an encrypted message that is 582 characters long. I know that: It is in hexadecimal It has been encrypted using a one time pad The pad's length is exactly 50 characters When the pad reaches ...
0
votes
1answer
29 views

Do RSA keys contain a checksum mechanism? [duplicate]

I'm new to cryptography, and I was making an experiment a few minutes ago, but I want to have some deeper knowledge about RSA public and private keys. I have a set of keys One begins with ...

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