2
votes
1answer
145 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 ...
1
vote
1answer
408 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. ...
0
votes
2answers
116 views

Create a field in PBC

Edited (I removed the emphasize on Integers): My question is partly cryptography and partly programming, I would appreciate any help on any aspect of it :) I want to use PBC library to do the ...
4
votes
5answers
664 views

Is it theoretically possible to construct a string that contain its own hash value?

After saw the xkcd comic self-description, I wonder is it theoretically possible to construct a self-descriptive string that contains its own hash value? Let's say the string's md5 value is ...
3
votes
2answers
635 views

Is there any implementation of scrypt that allows a specific limit on memory?

The answerer has commented that scrypt's memory use is "only a function of r". $\:$ However, he has not addressed my argument that it also depends on N, in one of my comments from over 5 days ago. I ...
1
vote
0answers
128 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?
6
votes
1answer
1k 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?
8
votes
2answers
2k views

Why is the P-521 elliptic curve not in Suite B if AES-256 is?

In the NSA's document, "The Case for Elliptic Curve Cryptography", we have ...
6
votes
2answers
2k views

Will our app be FIPS 140-2 compliant if we use our own AES algorithm implementation?

We are in the processing to understand if our software applications is FIPS 140-2 compliant or not. Currently in our application, we are using our own implementation of AES algorithm. AES is a FIPS ...
10
votes
1answer
11k views

How does RSA signature verification work?

I understand how the RSA algorithm works for encryption and decryption purposes but I don't get how signing is done. Here's what I (think) I know and is common practice: If I have a message that I ...
1
vote
1answer
252 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
2answers
218 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 ...
1
vote
1answer
201 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 ...
4
votes
2answers
2k views

Is a 1024-bit DSA key considered safe?

I created my PGP key in 2000. I’ve revoked the older, weaker sub-keys in favor of a 4096-bit RSA one, but the primary key is 1024-bit DSA. I read on Wikipedia that… NIST 800-57 recommends lengths ...
6
votes
2answers
799 views

Strength of CBC with Ciphertext Stealing

Is CBC with Ciphertext Stealing (CTS) considerably weaker than CBC with padding such as PKCS7? I would imagine the most common situation where CTS is necessary would be due to some size constraint of ...
6
votes
1answer
219 views

How relevant are hardware implementations of crypto algorithms?

All of the SHA-3 finalists discussed speed and efficiency of a hardware implementation of their algorithms. How relevant are such details? I'm curious about who commercializes hardware that ...
2
votes
3answers
489 views

Identification of correct plaintext after decryption in Rabin cryptosystem

In the Rabin cryptosystem, decrypting a message can produce four different outputs, of which only one is the correct plaintext. How can one know which of the outputs is the correct one?
4
votes
1answer
212 views

OMAC/CMAC constant for different block sizes

OMAC/CMAC only specifies constants for 64-bit (0x1B) and 128-bit (0x87) block size. I would like to know how to get constants ...
6
votes
6answers
838 views

Generate Elliptic Curve Private Key from User Passphrase?

I'd like to generate a private elliptic curve key from user input like pass phrase. Is the best way to do this with a key derivation function like PBKDF2? Is there a better way? Edit (based upon ...
2
votes
1answer
1k views

Am I insecurely implementing AES in Python? [closed]

My name is Pat, I'm a rising high school senior interested in Comp Sci. I've taken interest in cryptography following the NSA scandal. Since this is the first time I've ever implemented encryption ...
6
votes
1answer
176 views

Is there a security proof for the Triple-DES construction in the ideal cipher model?

Suppose one has an ideal block cipher $E \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \: \to \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w ...
6
votes
2answers
497 views

Why are HOTP and TOTP implementations all using 6 digits and not more?

I was checking the RFC's after wondering for some time. In RFC 4226 - HOTP: An HMAC-Based One-Time Password Algorithm, it states on the appendix: A simple enhancement in terms of security would be ...
3
votes
1answer
502 views

Textbook-RSA meet-in-the-middle attack against other RSA based schemes?

A “meet-in-the-middle” (not “man-in-the-middle”!) attack on textbook-RSA was presented to me. The only requirements for it was that the attacker gets the output of RSA and the public key, and that the ...
11
votes
4answers
838 views

Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext?

I am looking for a cryptographic hash function that can be computed by a human using only paper and pen without ever leaking any information about the plaintext on the paper. The cryptographic hash ...
1
vote
1answer
204 views

Relationship between Elliptic Curve Discrete Log, Integer Discrete Log, and Integer Factorization

I am trying to look into a relation between the following three problems which are widely used to build public crypto systems: Integer Discrete log Elliptic Curve Discrete log Integer Factorization ...
8
votes
2answers
211 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 ...
7
votes
3answers
1k views

Any practical uses of machine learning for cryptography?

I am about to go study for my masters in machine learning, data mining and high performance computing, but have recently become very interested in cryptography after taking Dan Boneh's Cryptography ...
0
votes
2answers
477 views

One Time Pad Question

I have a ciphertext encoded with One Time Pad. I do not know the key. How can I find the possible keys which when decoded, will result in a meaningful plain text?
10
votes
3answers
2k views

MIT says: mathematical theory behind encryption is wrong. What are the consequences?

A friend shared with me the following link: Encryption is less secure than we thought I'm not a security expert and could understand great part the article, except the section about noise, but what I ...
3
votes
2answers
148 views

Could this be a valid variation of the Schnorr protocol?

The Schnorr protocol is a 3-steps proof of knowledge of a discrete logarithm, whose interactive version works as follows. Let $p$ and $q$ be two public primes, such that $q \mid (p-1)$, and let $G$ ...
1
vote
2answers
239 views

What security flaw exists in MAC authentication scenario?

What security flaw exists (if any) in the solution of this non-encrypted authentication scenario? An unencrypted message passes one-way from computer A to B. Its transmission is viewable by the ...
6
votes
2answers
759 views

Vulnerabilities if encrypting the same data with 2 different keys

Let's say that Alice and Bob complete a key exchange and then Alice uses that key k1 to encrypt a 256-bit key kaes1 and sends it ...
0
votes
2answers
180 views

Is there a way to encrypt multiple sets of data into one result, with separate keys decrypting each set of data

What I am picturing is something like this: Block A: "Hello, how are you today?" Block B: "The weather reminds me of summer." I encode this, giving me two keys and a resulting encrypted block e.g. ...
5
votes
1answer
314 views

What criteria make the theta step of Keccak's round function reversible?

From what I've been reading, Keccak's round function is reversible. That's pretty obvious for the $\rho$, $\pi$ and $\iota$ transforms. For $\chi$ to be reversible, $x$'s range has to be odd — but ...
2
votes
1answer
146 views

Camellia cipher - is it a symmetric or asymmetric cipher?

I read a wiki page about Camellia cipher and know that it is a block cipher that can use 128-bit, 192-bit or 256-bit keys. But I cant find any information about if its a symmetric cipher (uses one key ...
4
votes
2answers
306 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. ...
4
votes
3answers
229 views

Can padding length, and thus plaintext length, be considered public information when using aes-cbc?

Right now I'm using a simple padding system that takes the plaintext, hashes it with SHA512, and appends $x$ bytes of the hash as padding where $x$ is the delta between the plaintext and nearest ...
5
votes
1answer
239 views

Why is the Pedersen commitment computationally binding?

This is how the Pedersen commitment seems to work: Let $p$ and $q$ be large primes such that $q \mid (p-1)$, let $g$ be a generator of the order-$q$ subgroup of $Z_p^{\star}$. Let $a$ be a random ...
2
votes
1answer
180 views

Public Keys on Social Media

Is there any problem with using social media (i.e. Facebook) as a directory of public keys? For example, couldn't Alice put a note containing $(g^a \bmod p, g, p)$ on her Facebook page so she could ...
1
vote
2answers
531 views

Is it possible to subtract/multiply numbers using homomorphic encryption?

Most of the libraries I've seen allow you to add encrypted numbers. Is it possible to subtract and multiply them?
10
votes
1answer
2k views

Technical details of attack on Android bitcoin usage of SecureRandom

Reports are surfacing that Android's Java SecureRandom class has issues and isn't totally secure. A specific example of how this issue translates to applications is bitcoin, where reports are stating ...
2
votes
1answer
406 views

Do companies like CipherCloud really have the option to use homomorphic encryption?

I was reading How is CipherCloud doing homomorphic encryption? and was wondering: Is there a technically feasible way for companies like CipherCloud to use homomorphic encryption (HE) while ...
4
votes
2answers
206 views

Fractal Merkle Traversal

I am studying Fractal Merkle Tree Traversal algorithm in this book. In the [pag. 54] I don't understand this paragraph: We may determine the number of pebbles returned at these times by ...
8
votes
2answers
2k views

Pre-image resistant but not 2nd pre-image resistant?

Are there any cryptographic hash functions for which there is a known pre-image attack, or a known second pre-image attack, but not both? The attack doesn't have to be practical - just anything that ...
4
votes
2answers
234 views

How to use salt when there is only one user

I am encrypting files for storage in an untrusted location, using a custom Java program to do that. There is only one user, but there are many files. I am using AES in CBC mode with PKCS5 padding, and ...
6
votes
2answers
2k views

RC2, RC4, RC5 key length

While reading the Wiki page on RC4 I noticed that the key size must be in the range of 40–2,048 bits. So should I understand like this, that I can have a key that has length of, lets say 333 bits? ...
0
votes
1answer
387 views

How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
8
votes
2answers
1k views

Why does DES use exactly 16 rounds?

Why does DES use exactly 16 rounds and not more or less than 16? What is the significance of using 16 rounds?
2
votes
1answer
134 views

Verify Messages to Embedded Device

I'm building an embedded device that I plan on distributing. Periodically the device will poll my server to check for updates and commands. I'd like the device to verify that any messages(JSON strings ...
3
votes
1answer
6k views

How does DES decryption work? Is it the same as encryption or the reverse? [duplicate]

If DES decryption is the same as encryption done in reverse order, then how can the reversed S-Box convert 4 bits into 6 bits?

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