5
votes
1answer
247 views

Non adjacent form of an integer is unique

I have tried to look up the proof for NAF (Non-adjacent form) being unique for every integer, but as far as I have seen, textbooks only mention it as a property of NAF, but no proof is given. Also I ...
2
votes
1answer
61 views

Is this transposition cipher information-theoretically secure for 1 message?

Given: $m = \{0,1\}^{n}$; a plaintext message of length $n$ encoded in binary $k = randomshuffle([0, 1, ..., 2n-1])$; A secret key consisting out of unique numbers between 0 and $2n-1$ in a true ...
2
votes
1answer
162 views

Asymmetric cipher with multiple public keys

Asymmetric cryptography is well known. You generate a private key. Using the private key you generate a public key. Then you can sign a message with the private key and check signatures using the ...
1
vote
0answers
55 views

How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $ \frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...
1
vote
1answer
284 views

RSA: Why must e be relative prime to phi(n) [duplicate]

I've got a question concerning fields used in RSA: Let's use the following symbols for my example: {p,q} = primes {e,n} = public key {d,n] = private key I learnt that an inverse element exists if a ...
1
vote
0answers
382 views

Montgomery Reduction

I'm taking a hardware cryptography class and working on a problem that focuses on Montgomery Reduction. So by definition: Computing a x b (mod N) Pick R, s.t. R > N, gcd (R,N) = 1 Compute N^-1 ...
0
votes
1answer
76 views

Which one these alternatives using authentication and encryption will solve this multiple-user database problem?

Which one these alternatives using authentication and encryption will solve this multiple-user database problem ? I'm trying to understand the field of cryptography, so I've started reading a ...
4
votes
1answer
163 views

Prime factorization

What is the largest integer that can be factored by modern algorithm like Msieve and GGNFS in a time less than 5 hours with normal computers? For example, can an integer like ...
1
vote
1answer
198 views

Encryption of plain text using stream cipher algorithm

We know that in stream cipher algorithms plain text and generated key are Xored byte by byte. Generated key depends on how much plain text there is and on that basis key will generate and plain text ...
0
votes
1answer
40 views

What is the signifcance of inside threat in “How to Construct Multicast Cryptosystems … Secure Against CCA2”

In How to Construct Multicast Cryptosystems Provably Secure Against Adaptive Chosen Ciphertext Attack, the paper states under preliminaries: We consider the scenario where a single party, called ...
7
votes
2answers
211 views

Has human-generated entropy ever been a real problem?

I know the topic of human brains generating random numbers has been discussed here and in Cognitive Sciences before, but I am interested in a particular part of it: In an introductory book to ...
0
votes
1answer
80 views

Swap $x$ and $k$ in GGM construction

I'm studying the Goldreich-Goldwasser-Micali construction from pseudo-random generators to pseudo-random functions. In this specific construction, assume $G:\{0,1\}^n\rightarrow \{0,1\}^{2n}$ is a ...
1
vote
1answer
632 views

Common Modulus Attack in RSA

Consider the following scenario: The Information Security Department (ISD) of an organization issues each of the organization's employees, domestic and abroad, with an individual RSA key. To simplify ...
0
votes
0answers
47 views

Generating interactive, secure multiple ECC key pairs deterministically

In Elliptic Curve Cryptography (ECC) assuming user A has a private public key pair of $S$, $P$ accordingly with generator point $G$ which as we know is: $$P=S*G$$ Assuming that user A wants to ...
0
votes
1answer
88 views

what is number of invertible matrix m*m on$ z_n$? [closed]

‎ ‎‎please help me what is number of invertible matrix $‎m*m$‎‎‎ on Group $\mathbb{z}_n$ ?‎‎‎, assuming we know‎ this number in $\mathbb{Z}_p \quad$ (‎p is prime‎‎) is $‎(p^{n}-1)(p^{n}-p) ...
5
votes
2answers
641 views

Why use randomness in digital signature algorithms?

I understand why randomness has to be employed in encryption, because deterministic ciphers are not IND-CPA. I don't understand why digital signature schemes that employ randomness, like RSA-PSS, are ...
0
votes
1answer
54 views

Deterministic outputs based on non-connected inputs

I am looking for a one way function that can generate outputs deterministically. However, revealing any of the inputs dont allow the person to generate other inputs. E.g: lets say we have a list of ...
1
vote
1answer
65 views

How are onetimepads distributed?

OTP encryption is unbreakable as it seems. I have read some stuff (wiki, blogpost, etc.) but i would not find any information how they are used. If i wanted to create a messenger service, how would i ...
0
votes
0answers
54 views

Determine encryption method with input and output

A website stores username and password in a session cookie. In the cookie the password is "encrypted" or modified in some way. Given that the "encrypted" version is always the same, I do not believe ...
1
vote
1answer
97 views

How to generate the APA SBox?

I am trying to generate the S-Box provided in the Affine Power Affine paper (PDF) but I'm not sure I understand it fully. The essence of the paper is this: ...
4
votes
0answers
75 views

Is the reverse of the “discrete logarithm problem” equally dificult? [duplicate]

It is not easy to understand why this becomes a hard problem. The discrete logarithm problem as defined here: “any integer k that solves $b^k = \{g\mod{n}\}$ is termed a discrete logarithm” i.e.: ...
2
votes
1answer
117 views

NTRU and one failed example

In NTRU crypto system I have used these polynomials and parameters: $N = 17, p = 7, q = 64$ and $f$ as private key is: $$f = -1 + x + x^2 - x^4 + x^6 + x^9 - x^{10}$$ So the inverse of $f$ in ring ...
0
votes
1answer
72 views

SSL certificate / SSL configuration - FIPS-197 compliance

What does it mean when we talk about FIPS-197 compliance in the context of SSL certificates, their deployment and usage ? I am almost certain that the FIPS-197 compliance in the context of SSL ...
9
votes
1answer
180 views

Can Grover's algorithm be parallelized?

Using a quantum computer, Grover's algorithm can search an unordered list of length $N$ in time $\sqrt{N}$. Applied to cryptography this means that it can recover $n$ bit keys and find preimages for ...
3
votes
1answer
138 views

Double-and-add/Montgomery VS blinding

I'm having a hard time understanding why people use constant-time techniques to counter time-attacks, when blinding seems as good and cheaper to implement. Why do people avoid blinding in ECC?
4
votes
1answer
240 views

What is the “compression function” in Merkle-Damgård?

Is the "compression function" in Merkle-Damgård just a collision-resistant, one-way hash function but one that operates only on fixed size inputs? If so, is MD just a way to extend it to work on ...
2
votes
2answers
543 views

How does a certificate authority issue a digital certificate?

I am new to cryptography and I want to know the details of how a Certificate Authority issues a digital certificate. From what I know (please correct me if I'm wrong at any parts of my explanation): ...
0
votes
1answer
75 views

Key distribution and computation for homomorphic encryption

How can a system where the party performing a computation also possess the private key and still not know the answer of computation be designed ? Also the other party who does not have the private key ...
0
votes
0answers
94 views

side channel attacks against TDES (compared to AES)

We all know AES has some pretty strong side channel attacks, some where (with a couple of hundred know plain- and ciphertext combinations) a key can be derived in a matter of minutes. Others may take ...
2
votes
2answers
91 views

Authenticated EC key exchange without a signing/signature scheme?

From my little understanding of EC-based authenticated key exchange protocols, I believe that it is not possible for authenticated key exchange without a signing/signature scheme. Is this correct? ...
3
votes
1answer
220 views

Elliptic curve cryptography G*G

I understand how ECC works for the point multiplications and stuff. All we normally do is to multiply a scalar number (lets say d as a private key) with the base point generator ...
0
votes
1answer
109 views

Verification of Pinocchio (verifiable computation)

I am reading the Pinocchio paper. The calculated result $y$ is a part of the verification input, but it seems to me, the verification procedure does not utilize the result $y$. Can anyone can help me ...
0
votes
1answer
242 views

Super-simple encryption of short strings

I want to anonymise the initials of experiment participants by giving each a pseudonymic set of initials, by encrypting their true initials. Their initials are only two or three letters in length. ...
1
vote
0answers
52 views

Cache Attacks on Cloud Infrastructures

I read something about cache attacks like this: Enter KSM (Kernel SamePage Merging). KSM enables the kernel to examine two or more already running programs and compare their memory. If any memory ...
1
vote
2answers
83 views

Is a padding oracle attack possible if data is only encrypted internally on a server (e.g. for storage)?

I read something about the padding oracle attack when analysing the use of an AES-encryption of data in a database and was "scared" it could be a serious issue. But after investigating a bit further, ...
0
votes
1answer
57 views

Why rogued certificate from hash collision is harmful

I cannot understand why rogued certificate is thought harmful though It can be used to impersonate some website. The attacker can craft a rogued certificate with different identities and public key ...
1
vote
1answer
122 views

What is SHA-256 in Conjunctive Normal Form?

What is the conjunctive normal form (CNF) representation of $\text{SHA-256}(m)=h$, where $m$ is of fixed (or bounded) size and $h$ is 256 bit?
2
votes
1answer
144 views

Known plaintext attack on 3 round SIMON block cipher

I am attempting to write a program to perform a linear approximation attack on a reduced round version of the SIMON block cipher, but I am stuck on how to actually apply the linear approximation to ...
4
votes
0answers
110 views

Under what conditions did a Bletchley bombe stop?

I am trying to understand the conditions necessary for one of the Bletchley Park bombes to stop. Let me give an example. I have been experimenting with Enigma machine and bombe simulators to try to ...
9
votes
0answers
356 views

Is it possible to break enigma code with a todays laptop [closed]

I have a 500 characters enigma encoded text. Random rotors were used (not the ones from wikipedia). I know of this flaw. I can guess some words that sould be in the text, but this probably doesn't ...
1
vote
1answer
66 views

DHKE choice of private keys

In some literature it is written that the private key should be chosen random from {2,3, ..., p-1} and in some it says {2,3, ..., p-2} I guess p-1 is a weak private key, but why is that so? The ...
4
votes
1answer
194 views

what are the NTRU keysize and application in industry ?

I'm a student currently working on a research project on the NTRU cryptosystem, I've read some papers about this cryptosystem, and in those papers they are talking about keysize, is it the size of the ...
0
votes
0answers
100 views

Rabin cryptosystem with 1 mod 4

We have p and q which are distinct primes congruent to 1 mod 4. Then we have n = p*q. Do you know any algorith for calculating square roots for the decryption in this case? I'm asking for some ...
0
votes
2answers
187 views

Are there drawbacks to encrypting data locally before being encrypted in cloud backup (multiple encryption)?

I am planning on backing up my hard drive using a cloud backup service but have become skeptical of the industry based on incidents like these: ...
1
vote
1answer
79 views

Is there any patent free EC point compression available? If not, should I GPL/LGPL my code?

I'm currently using the BouncyCastle implementation in uncompressed mode, and considering releasing an optimized version of EC code that uses point compression. It appears the only thing limiting me ...
0
votes
1answer
54 views

Different keys for clients but 1 key on server

Is it possible to have different keys on alot of (embedded) devices and just have 1 key on a server (to witch all these devices connect)? The main point here being when 1 device is compromised this ...
1
vote
2answers
229 views

correct usage of keys and nonce

I've being studying up on AES, GCM, CBC, HMAC and a lot of other primitives and am somewhat ( a little bit, perhaps) familiar with them however I am still a bit weary on the use of the keys and nonce. ...
7
votes
1answer
451 views

The difference between MAC algorithms and what to use

I've been looking into message authentication codes and found several ways to create integrity for a message. I know of the following algorithms: HMAC, this can use any cryptograhpic hash function ...
0
votes
2answers
89 views

How is the MAC or HMAC secret shared with the other party for verification?

I've seen people everywhere say to use a MAC or HMAC with block ciphers. I think I understand the basics, but I'm still not sure how the HMAC secret is distributed so the other party can verify that ...
1
vote
0answers
140 views

Security of basic SHA256 MAC in an authenticate-then-encrypt scheme

I know the following construct is insecure if the MAC as defined below is appended to the encrypted message in an Encrypt then Authenticate (EtA) scheme. $k_1$: encryption key $k_2$: authentication ...

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