3
votes
2answers
519 views

Finite fields and ECC

I understand modular arithmetic(or at least I think I do!) and I've tried to read and learn about how the Math in RSA works(and I think it went pretty well). I've been reading up on ECC and it looks ...
10
votes
3answers
764 views

Should I delete cryptographic data from memory?

When dealing with cryptographic data, is there a chance that attacker recovers portion of data I used in my program? Should I try to delete every bit of keys and encrypted data that I used, overwrite ...
5
votes
1answer
129 views

Authentication protocols for authenticating devices to a server

The requirement is to authenticate 1000s of devices to a server when the devices try to contact the server. The problem I face is that all authentication protocols require some kind of shared secret ...
1
vote
0answers
40 views

How does a cracker know if they've broken AES-CBC encryption? [duplicate]

How does a cracker know if they've broken CBC or stream encryption? With hashe cracking one would know because you have the password that you started with to test. But for CBC decryption, you have a ...
4
votes
1answer
381 views

Why no swapping block in the last round of DES?

Round 16 on the encryption side, and round 16 on the decryption side of DES have no swapping module. Why is it like this? Can anyone provide any justification? This is my homework question.
7
votes
1answer
2k views

Is AES-XTS considered safe to encrypt multiple files with the same keys?

I was wondering if changing the cipher mode to AES-XTS in EncFS would be a sound idea. EncFS uses AES in CBC mode until the last 1KB block, and CFB mode for the last block if ...
1
vote
3answers
991 views

Lagrange Interpolation for finite field GF(2^8), for Secret Reconstruction

I'm using Lagrange's Interpolation technique to reconstruct the secret from a set of point pairs (x,y). Since I only need the secret, not the whole polynomial, I have simplified the reconstruction ...
5
votes
1answer
1k views

KDF and number of iterations for GPG

I gather, from reading the GPG manual, that symmetric encryption based on a password uses one of a variety of Key Derivation Functions (KDF). Although not explicitly mentioned I assume that PBKDF2 is ...
3
votes
1answer
401 views

Elliptic curve parameter generation

I am curious of the details of how one would go about generating elliptic curve parameters. (I know standardized parameters exist, but I'm trying to understand both how they were generated and the ...
3
votes
1answer
303 views

Quantum resistance of Lamport signatures

The Lamport-Diffie signature scheme is said to be quantum-resistant. Why is that? What would a quantum attempt to attack this signature scheme look like, and how does it fail?
1
vote
1answer
189 views

The “Square Root” Solution of Oblivious RAM Simulation

I am reading the paper Software Protection and Simulation on Oblivious RAMs by Oded Goldreich and Rafail Ostrovsky. And I wonder about the description of the "Square Root" solution of oblivious RAM ...
2
votes
3answers
793 views

Implementing a one-time pad without binary?

This is a program that I found which takes a purely alphabetical message, converts the letters to their ASCII values and combines them with the ASCII values of an alphabetical key (wrapping around ...
1
vote
2answers
807 views

Quadratic residue problem on composite integers

Its believed that the quadratic residue modulo $n=p·q$ for large primes $p$ and $q$ is intractable, which forms the basis of some cryptosystems. However, it is solvable if the factors of $n$ are ...
6
votes
1answer
6k views

Multiplication/Division in Galois Field (2^8)

I'm attempting to implement multiplication and division in $GF(2^8)$ using log and exponential tables. I'm using the exponent of 3 as my generator, using instructions from here. However I'm having ...
11
votes
1answer
388 views

What is the origin of the word “Keccak”?

Where does the word or acronym Keccak come from? Guido Bertoni, Joan Daemen, Michael Peeters, and Gilles Van Assche. Keccak sponge function family main document. Submission to NIST (updated), 2009. ...
5
votes
3answers
1k views

Convert old and busted password encryption to something sensible

Given a TOTALLY HYPOTHETICAL scenario in which passwords for over a million accounts in over 200 databases have been stored using 3DES, a key derived from a (single) MD5 hash of a customer-controlled ...
4
votes
1answer
18k views

What is the “shared secret” used for in IPSec VPN?

Can somebody explain what the "shared secret" and "password" do when opening/creating a VPN tunnel? In this specific case I setup a VPN to my Fritz!Box and I had to provide a shared secret (which was ...
3
votes
1answer
802 views

Generating an IV for ESP 3DES-CBC

I have an application written in C, running in Linux. It uses IPsec (ESP) (manually putting the IPSec packet together) to send certain packets. The algorithm used ...
5
votes
1answer
438 views

Why is TLS SRP verifier based on user name?

I don't understand why TLS SRP (or SRP in general) includes the user name in verifier calculation, given that user name is basically public. From spec RFC 5054 $x$, which is then used to calculate ...
-1
votes
1answer
78 views

Is size Q equal to size SHA(Q)? [closed]

Assume d is a 128 bit random integer and P is base point of an elliptic curve and Q = dP is a point on the elliptic curve and SHA is a hash function with 128 bit output, my question is: Is size Q ...
6
votes
1answer
247 views

multiple keys via HKDF - whats better, one or two applications of HKDF-extract

Assume for the sake of the question that I have two variable-length bit strings, each with 128 bit cryptographic randomness, and I want to extract two 128 bit keys via HKDF-SHA256. Which alternative ...
6
votes
1answer
658 views

What does ''latency'' really mean when a block cipher is partially unrolled?

Typically,I think latency should mean the time from the first plaintext input to the first ciphertext output, when the block cipher is not totally unrolled (such as AES unrolled with 2 rounds). If I ...
1
vote
1answer
134 views

Three-way key exchange with elliptic curves without pairing

Assume that there are three users, each with their own secret key $d_i$ and the corresponding public key $Q_i = d_i \cdot P$, such that $Q_i$ is a point on an elliptic curve and $P$ is a base point on ...
-7
votes
2answers
278 views

Snowden Challenge II: Can we solve Snowden challenge quantumly? [closed]

Suppose that tomorrow is July 7, 2050 and Snowden is still stayed in Sheremetyevo airport. Further, let us suppose that quantum computation and quantum commincation are available to everyone, and ...
2
votes
2answers
148 views

Security of CFB on a public channel

Given a server that broadcasts all received data to all connected peers (except the sender), two participants can have an encrypted conversation using a self-synchronizing method like CFB and some ...
3
votes
2answers
281 views

No IV for one off symmetric file encryption

My question is (hopefully, for somebody) a simple one; but my project is holding as I'm not sure. I read on SO that generating encryption keys without an IV is a bad idea, so is using a constant IV ...
3
votes
2answers
789 views

Encrypted counter as IV in CBC mode encryption using same key

I'm currently working with a secure transport protocol that defines the IV to be a counter (incremental nonce) to be encrypted with the same key. This is a followup to a protocol that did not provide ...
4
votes
4answers
377 views

Can cryptography be used to hide routing information from the router?

If Alice wants to talk to Bob and she has to involve a third party system run by Carol to establish, and possibly maintain, communications, then Carol knows that Alice and Bob communicated with each ...
2
votes
3answers
242 views

Secure communication between multiple peers on a public channel

I am wondering how can I secure communications between multiple peers over a public channel, like an IRC channel. With two peers it is easy - they exchange their encryption keys and decrypt the ...
1
vote
1answer
403 views

Does CBC encryption of a hash provide authenticity?

Given a message $M$ and a cryptographic hash function $H$, let $f(M) = E_K(M || H(M))$ where $E_K$ is AES-128-CBC encryption with PKCS#5 padding. Take $H = \textrm{SHA-256}$ if it matters. In other ...
3
votes
2answers
374 views

Is it possible that two distinct RSA moduli share both of their prime factors?

I am using an algorithm (can be found here1) that can compute efficiently the GCD of multiple RSA keys. It intended for RSA keys that were generated with low entropy and may have one of their primes ...
7
votes
2answers
392 views

Why have hashes when you have MACs?

It would seem to a naive eye that if you have a MAC, you have a hash function: use a key that all the parties know (such as all-bits-zero). A potential application would be a resource-constrained ...
6
votes
1answer
730 views

What signature schemes allow recovering the public key from a signature?

It seems to be possible to retrieve the (public) key used for creating an ECDSA signature just from the signature alone. This seems like an interesting property; as far as I know, RSA doesn't share ...
8
votes
3answers
416 views

Can one have an authentic, but repudiable, message without a previously shared secret?

Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else. If I understand right, this means that the same message could have ...
1
vote
0answers
637 views

Keepass Twofish plugin security

Keepass is a well known open-source password manager program, with plugin support. One of the offered plugin is a twofish encryption mode of operation in lieu of the build-in AES algorithm ...
-2
votes
1answer
164 views

what is pairing in cryptography? [closed]

Let $G_1, G_2$ be additive groups and $G_T$ a multiplicative group, all of prime order $p$. Let $P $ in $G_1, Q $ in $G_2$ be generators of $G_1$ and $G_2$ respectively. A pairing is a map: $e:( ...
1
vote
2answers
227 views

How resilient to attackers with extreme resources available is this encryption method?

How could the following scheme be made more resilient to attacks capable of utilizing massive amounts of resources? Assume all random values are cryptographically secure. Key derivation: scrypt ...
2
votes
1answer
190 views

SHA256 Round Equivalence

I have calculated the average number of operations in 1 round of SHA256 as follows: Additions: 9.25 Bitwise Rotations: 9 Bitwise Shifts: 1.5 Bitwise AND: 5 Bitwise XOR: 10 I have certain ...
2
votes
1answer
153 views

Multiple parties must encrypt and get the same result

Hopefully this question is not too simple - I did some research but with encryption I really don't want to make a mistake. Our scenario is that multiple groups need to encrypt a number and arrive at ...
3
votes
4answers
1k views

random number generator 10-side dice alternative

A lot of sites (e.g. Dirk Rijmenants') refer to 10-side dice to generate random number for one-time-pad. I was thinking about new ways to generate random numbers, letters and passwords. here what I ...
1
vote
1answer
1k views

Is the salt value a secret or can it be stored in cleartext just like the IV? [duplicate]

From Wikipedia I read that the IV is used to randomise the mapping of cleartext to cipher text and that the IV is usually stored (in cleartext) together with the encrypted record. ...
5
votes
1answer
371 views

Must the order of the groups in a bilinear map be the same?

I've been reading up on bilinear maps and their application to cryptography and one thing I keep seeing hasn't yet clicked. If $e:G_1\times G_2\to G_n$ is a bilinear map, $G_1,G_2,G_n$ are always ...
9
votes
2answers
14k views

How can Cipher Block Chaining (CBC) in SSL be attacked?

I am trying to understand how CBC-mode in SSL/TLS can be attacked. I have been looking around online but all examples and explanations are very hard to understand and follow. Can you give a simple ...
4
votes
2answers
3k views

what kind of hash function can provide a short hash and be collision resistant?

When you try to connect via SSH, you see a signature which is short but I heard it is even stronger than sha256. It is perhaps stronger because it uses more rounds. Is there a hash function or a ...
6
votes
1answer
2k views

RSA random prime generator

What is the current standard of random bit generators? RSA relies on two large prime numbers, and I am wondering what is the algorithm used to generate such numbers?
1
vote
0answers
154 views

Can anyone explain most popular RSA attacks like I'm 5?

Suppose I implement RSA myself in C and I use just the formulas from number theory. What attacks would my implementation be vulnerable to? Can anyone explain this to me like I'm 5?
1
vote
1answer
499 views

Understanding the “cube-root math” behind an RSA signature forgery

I'm trying to understand the math outlined in this paper on a RSA signature forgery attack. I understand it except for one aspect of how the cube root (that makes the forged signature) is computed. ...
1
vote
1answer
259 views

Brute force attack on RSA - success criteria?

In a hypothetical discussion we ended up with a concrete question I'd like to find the answer to: If you try to brute force an RSA encryption, but the original vale which was encrypted was just ...
5
votes
2answers
406 views

Is there any research about cryptography on nondeterministic Turing machines?

I know it's a highly theoretical topic, but I was wondering if there was any research out there about what cryptography would be like assuming that we had access to nondeterministic Turing machines. ...
8
votes
2answers
216 views

Voting scheme where the votes become public when a threshold is reached

Does there exist a voting scheme where voters cast private encrypted votes that automatically become public only after the threshold number of votes is cast? It needs to be done without a central ...

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