4
votes
1answer
128 views

When would one prefer a proof of knowledge instead of a zero-knowledge proof?

I've just realized I find it hard to distinguish between these two terms (proof of knowledge, and zero-knowledge proof), specially where only the latter seems to be used in many cryptographic ...
4
votes
3answers
303 views

What crypto system allows for 3 parties: Party 1 who makes an assertion, Party 2 mutates the assertion, Party 3 validates it

I'm looking for the cryptographic equivalent of a Drivers license where the issuer can be verified, the issuer doesn't need to know who you showed the drivers license to, but also allows ...
2
votes
1answer
159 views

What are the possible cryptographic implications of Zhang's proof of the Twin Prime Conjecture?

Earlier this year, Yitang Zhang published a proof of a weakened form of the Twin Prime Conjecture. I'm wondering if any of the new mathematical machinery he developed has uses in cryptography or could ...
1
vote
0answers
58 views

How does Dissent protect against Sybil Attacks?

Dissent claims to be able to be resistant to Sybil attacks. Dissent seeks to offer accountable anonymity, giving users strong guarantees of anonymity while also protecting online groups or forums ...
2
votes
1answer
216 views

random number generator and seed

I'm working with openssl cryptographic libraries, I'm new to all these cryptographic stuffs and slowly I'm learning all these. I have a doubt regarding random number generator, I'm using ...
4
votes
2answers
356 views

Provable Encryption

Is it possible to encrypt data in a way that it can be proven that the data is encrypted, without revealing the key? Alice chooses some plaintext, then she encrypts it with a certain scheme. She ...
2
votes
3answers
564 views

Using Whirlpool hashing function to encrypt data

I've read that the Whirlpool hash function can produce footprints that could be used as a pseudorandom generator. Is it "OK" to use it to encrypt some data using something like the following? ...
6
votes
2answers
634 views

What is the security loss from reducing Rijndael to 128 bits block size from 256 bits?

As you know in the past few weeks it has emerged that NIST/NSA have been involved in weakening encryption standards over a long period of time so that they can retain the ability to break encryption ...
1
vote
0answers
513 views

How is the initial permutation of DES created?

I am creating a program in C language with DES (Data Encryption Standard) functionality, but don't know how to apply the initial permutation. Is it achieved by swapping the values? If "yes", then ...
6
votes
2answers
1k views

GPG symmetric encryption and javascript

I have a use case where I need to encrypt some text in the browser using javascript. Only the encrypted text will be stored on the server. The user should then be able to take the encrypted result and ...
9
votes
3answers
573 views

Counter mode secure hash algorithm

Ever since the SHA-3 competition, I've been wondering if it is possible to create a hash algorithm that is easier to parallelize. The current algorithms all seem to require building a tree of hashes. ...
1
vote
0answers
51 views

Algorithm for sharing secret information with redundant keys [duplicate]

I have an information that I would like to encrypt and give it to someone else. I would like to encrypt it using N separate passwords (say 5) and give each password to some other persons. However the ...
4
votes
2answers
215 views

Is this a structural weakness of Feistel networks?

I'm doing a lot of reading about Feistel networks. Something occurred to me a bit ago that I hadn't realized previously, namely that in any Feistel construction there are bits of the plaintext that ...
5
votes
1answer
104 views

Is there any existing analysis for this construction to turn a tweakable blockcipher into a PRF?

I'm basically looking at this construction to turn a tweakable blockcipher $E_c(x)$ taking a key $k$, nonce $n$, counter $c$ (forming tweak $t = c||n$) and an input $x$ into a PRF on an ...
6
votes
1answer
315 views

Can a nested block cipher avoid the meet in the middle attack by using a secret initialization vector for the inner encryption?

It seems to be believed that encrypting twice with a block cipher using an independent key each time is not as secure as you might expect because of the "meet in the middle" attack. This is an attack ...
3
votes
4answers
448 views

Verify product without revealing multipliers

Situation: Several participants contribute encrypted random numbers. These numbers will be used to generate community-agreed random (by simple multiplication). Question: Is there any way to detect ...
3
votes
2answers
418 views

Are there public slow-but-strong algorithms out there that resist brute-force attacks better?

I'm reading that AES uses 4x4 bytes (4*4*8 = 256 bits key) matrix for performances matters (since it's a requirement for common standard encryption algorithms), but are there implementations with ...
1
vote
1answer
324 views

Dual_EC_DRBG and OpenSSL on a Mac

Since there is not much info anywhere on the Internet related to this: Does anyone know if OpenSSL's default CSPRNG is Dual_EC_DRBG or not? Their wiki is not very clear… Related to the first ...
1
vote
1answer
437 views

RSA Decryption with Private Key but no public exponent

I manually set the RSA private key, given the private exponent and modulus. When I use this key to decrypt a message encrypted using a public key (also set with public exponent and modulus) seems to ...
1
vote
1answer
2k views

Counter Mode in Advanced Encryption Standard(AES) Algorithm

In Advanced Encryption Standard, if I used "Counter Mode", how should I handle the nonce? Should I divide the nonce value into two? For example: I have 128-bit of nonce, should I divide it so I get ...
2
votes
1answer
249 views

Is it safe to use GZIP to avoid padding related attacks

I am designing a library that supports encrypting some in-memory data using AES in CBC mode. Now I need a padding but it seemed to me that Apple's CommonCrypto library and OpenSSL have different ...
2
votes
1answer
200 views

How does Poly1305 in the NaCl library calculate a MAC?

I've been reading about Poly1305 as implemented in the NaCl library, more specifically I've been referring to this Java implementation of NaCl. My understanding of XSalsa20Poly1305 (in this ...
1
vote
2answers
613 views

Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1

I am interested in the theoretical consideration of the bit strength of an encryption key and its precursor. Assume a given environment as follows: a. My encryption algorithm is AES-256 b. My key ...
6
votes
5answers
2k views

Is it possible to make time-locked encrytion algorithm?

I'm not sure if what I'm asking is even a valid question but here goes. Would it be possible to add a mechanism to an encryption algorithm that would mean it had to be a certain time of the day or a ...
1
vote
1answer
196 views

chaining rsa with ecies

In an answer to a previous question it was suggested that one way to protect your asymmetrically encrypted AES-256 keys, from say a solution to prime factorization, would be to chain asymmetric ...
2
votes
1answer
349 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 ...
2
votes
1answer
1k views

Cryptanalysis Affine Cipher: Brute-Force Search Vs. Meet-in-the-middle

Affine Cipher: $Enc(x) = (ax + b) \mod m$ $Dec(x) = a^{-1}(x-b) \mod m$ For a brute-force key search, we need to do $a \cdot b$ encryptions in the worst case. For a meet-in-the-middle attack, how ...
3
votes
1answer
351 views

Where is the S-Box generated in Rijandel/AES?

It's rather kind of lame questions, and I can't find good and clear explanation: In which step of Rijandel is S-box generated? Is the S-box reused in every round of cipher or is generated in every ...
2
votes
1answer
626 views

Meet-in-the-middle with checking complexity

In regards to meet in the middle type attacks, I have been considering the amount of operations in order to successfully find a key given two sets of plaintext / ciphertext pairs. All of the sources I ...
12
votes
1answer
4k views

What to watch for with openssl generating weak keys? (low entropy)

(Disclaimer: I am regular software engineer with only basic crypto knowledge, so helpful if can be explained for a layman.) I am concerned about generating weak keys on a shared linux box with ...
2
votes
1answer
181 views

Bandwidth and block size for Paillier cryptosystem

Can someone clarify what is meant by the terms cryptosystem bandwidth and block size for public key cryptosystems; The context is the Paillier cryptosystem and its Damgard-Jurik generalisation. My ...
-3
votes
1answer
298 views

List of available symmetric & assymetric ciphers [closed]

I was looking all over the Internet list of ALL existing symmetric and asymmetric ciphers. I know that there's, for example, AES, DES, Blowfish, DSA. But how about more? Where to find such list?
7
votes
1answer
2k views

Assuming a 1024qb quantum computer, how long to brute force 1024bit RSA, 256bit AES and 512bit SHA512

Assuming in the future there was a functioning 1024 qubit quantum supercomputer and it could run Shor's algorithm or Grover's algorithm to crack encryption very quickly. I'm interested in how the ...
1
vote
1answer
689 views

Reusing keys with AES-CBC

I heard that key/IV pairs must not be reused in AES-CTR, or when using any stream cipher for that matter. Yet the attacks described do not seem to apply to AES-CBC. Is reusing the same key several ...
3
votes
1answer
2k views

RSA cracking: The same message is sent to two different people problem

Suppose we have two people: Smith and Jones. Smith public key is e=9, n=179 and Jones public key is e=13, n=179. Bob sends to ...
7
votes
1answer
364 views

Is SSH public key authentication weakened by 'none' cipher?

As far as I know, SSH2 first does a key exchange based on the server host key and brings up transport authentication and encryption derived from this kex. The real authentication (password or public ...
0
votes
1answer
205 views

Is my understanding of CPA indistinguishability experiment correct?

Following are steps to conduct Chosen Plaintext Attack (CPA) indistinguishibility experiment $PrivK_\mathcal{A,E}^{eav}(n)$. $\mathcal{A}$ is the adversary $\mathcal{E}$ is the encryption scheme ...
2
votes
2answers
79 views

How to get the same calculation result on an untrusted computer, while withholding some information?

Consider this command on a trusted computer: result = function(public data, secret data) or shorter: r = f(p,s). How could a ...
3
votes
2answers
457 views

Theoretical pi-based stream cipher

Let's pretend that all digits of pi are known and arbitrarily long sequences of digits are trivial to get. Further, some mathematician proves that there are no patterns in pi. We could create a stream ...
3
votes
1answer
520 views

Proof that IND$-CPA implies IND-CPA?

I've read a few papers recently that used a notion of security called "indistinguishability from random bits/strings" under chosen plaintext attack, also called IND\$-CPA. See e.g. ...
2
votes
1answer
211 views

some of my confusions about DDH assumption

The wiki defines the decisional Diffie–Hellman assumption as follows: Decisional Diffie–Hellman assumption Consider a (multiplicative) cyclic group $G$ of order $q$, and with generator $g$. The DDH ...
4
votes
3answers
348 views

Can we design a public-key infrastructure without certificate authorities?

In a recent essay, Bruce Schneier tasks the engineering community with redesigning and rebuilding the vulnerable parts of the Internet's backbone. We need to figure out how to re-engineer the ...
-1
votes
1answer
103 views

Can someone explain how this unpadded RSA formula works?

Taken from http://en.wikipedia.org/wiki/Homomorphic_encryption, $\mathcal{E}(x_1) \cdot \mathcal{E}(x_2) = x_1^e x_2^e$ $\bmod\; m = (x_1x_2)^e \;$ $\bmod\; m = \mathcal{E}(x_1 \cdot x_2)$ What is ...
0
votes
1answer
59 views

blinding a hash vs. sending the hash directly

So with blind signatures you have two parties - A and B. A has a message that they want B to sign so A creates a hash of their message, blinds it, and then sends it to B to sign. That, as I understand ...
3
votes
2answers
188 views

Using single EC cert/keying material to derive symmetric encryption key (for storage)?

The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" ...
10
votes
2answers
723 views

Why would anyone use an elliptic curve with a cofactor > 1?

In cryptography, an elliptic curve is a group based on a finite field $GF(p^k)$; this group has $n$ elements on it, and we work on a prime-sized subgroup of size $q$. We denote the value $h = n/q$ as ...
6
votes
1answer
1k views

Is there a hash function which has no collisions?

Is there a hash function which has no collisions? To clarify: it would be some function which would produce variable-length output, and never produce the same output for differing input. It would ...
3
votes
1answer
232 views

What's the most secure way to derive a key from a password repeatably?

I'm trying to write a cloud storage application where everything the user uploads is unreadable by the server, encrypted client-side before being sent. Currently, the flow looks like this: User ...
3
votes
1answer
189 views

How would I make a secret notation alphabet more secure?

Disclaimer: I was looking for a place to ask this question on SE and this site seems to be the most fitting. If this question doesn't belong here, feel free to redirect me. Just out of boredom and ...
1
vote
1answer
147 views

Generating keys with HKDF from Diffie Hellman agreement

In order to generate multiple session keys from a Diffie Hellman key agreement protocol, I'm trying to use the HKDF to generate this session keys. The HKDF algorithm uses an Extraction-Expand ...

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