2
votes
0answers
105 views

How hard is a known prefix hash preimage attack?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
1
vote
0answers
283 views

RSA and One Time Password (OTP) service

What is the expert cryptographic opinion on the following? Assume that there is a web server and a client on web page. User on the Client calls an OTP web service on the server which: creates a RSA ...
4
votes
1answer
635 views

Commitment scheme using hash functions

Let's say Alice and Bob are playing a game where Bob is trying to guess a number Alice has chosen. Alice chooses a key $K$ and a number $N$ at random and performs $C=Commit(K, N)$ where $Commit(K, ...
5
votes
3answers
308 views

Designing a key expander out of ciphers

Is it possible to compose or combine $n$ ciphers ($cipher_0, cipher_1, ... cipher_n$) in such a way that they generate $n$ ciphertexts from the same key, $k$, and that recovering the key, $k$, from ...
6
votes
3answers
2k views

Encryption/ciphers/codes in Chinese

I am quite curious as to how you can perform simple encryption for the Chinese language. Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
2
votes
1answer
266 views

Increase number of rounds for SPN and Feistel ciphers

Read a post on Schneiers blog (and again 2011) about increasing the number of rounds for AES from to "AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds" to raise the security. ...
7
votes
2answers
270 views

How to do a literature search

How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ...
1
vote
0answers
134 views

More technical details on the ongoing (alleged) Chinese cyberattacks [closed]

Recently, there has been quite a lot of news about the Chinese compromising various US weapons systems and stealing military designs through "cyberwarfare". I am reading the news sources about these ...
10
votes
3answers
396 views

How broken is a xor of two LCGs?

Suppose we define a PRG as the xor of two LCGs modulo a 64-bit prime: something like the following Python code. ...
2
votes
0answers
329 views

Understanding elliptic curve encryption

I'm having a hard time understanding the elliptic curve encryption. One thing thing I don't understand is listing all the points on the curve (mod p). Suppose I have the following elliptic curve: y^2 ...
6
votes
4answers
3k views

Is there any opensource white-box implementation of AES or DES?

I googled it and give me no result. There is a binary executable of white-box implementation of DES (scroll down), but no source code provided. The same page also links various papers about ...
2
votes
1answer
392 views

Why must curve25519 shared secret be hashed?

When using the curve25519 DH function, D.J. Bernstein recommends hashing the shared secret before using it as a session key for a symmetric block cipher. Why is that? Hashing won't increase the ...
13
votes
3answers
779 views

Are NIST's changes to Keccak/SHA-3 problematic?

NIST is working on standardizing SHA-3. They have selected Keccak as the basis for SHA-3, and they plan to make some small changes to it; the result (with NIST's changes) will be standardized as ...
2
votes
0answers
30 views

Detail about reactive simulatability framework

I'm trying to understand the framework of reactive simulatability using *"PfWa2_00AsyncModel"* from this publication which is a tech report behind the paper A model for Asynchronous Reactive Systems ...
7
votes
1answer
798 views

How can I determine the GPG/PGP key ID from the RSA modulus?

According to http://www.pgp.net/pgpnet/pgp-faq/pgp-faq-keys.html#key-public-key-forgery, key ID is some lower bits sequence from the modulus (i.e. the $n$ variable): A PGP key ID is just the ...
3
votes
1answer
204 views

Friedman Index of Coincidence, pruning multiples of the keylength

I'm trying to write a Vigenere decipher script. I defined a couple of possible keylengths using the Kasiski method, using roughly this method: find recurring strings in the ciphertext between 3 and ...
1
vote
1answer
194 views

how to mathematically prove a key exchange algorithm [closed]

I want to know the basic methodology that can be used to prove that a key exchange algorithm is secure. I am not asking about any specific algorithm. I want to know what should be proven and how to ...
3
votes
3answers
254 views

How to attack a fixed LCG with partial output?

To show some colleague programmers exactly how broken C's rand() is (at least on Windows) I decided to break it. So everyone knows the exact parameters, MSVC's ...
3
votes
2answers
650 views

Why does Shamir's Secret Sharing Scheme need a finite field?

I read ampersand's question "Necessity for finite field arithmetic and the prime number p in Shamir's Secret Sharing Scheme", where he asked why Shamir's Secret Sharing Scheme uses arithmetic in a ...
13
votes
4answers
621 views

Could one construct a cipher that is secure for friendly parties to use but insecure for hostile parties?

Consider the situation of a nation state (Blue) at war with another nation state (Red). Blue wants to deploy a secure cipher that blue currently can not break, but they are considered that Red could ...
10
votes
2answers
810 views

Why was the winner of the AES competition not a Feistel cipher?

The winner of the AES competition has a structure that does not qualify as a Feistel cipher, as explained in answers to this recent question. However, most many of the AES candidates, and all 3 out ...
4
votes
1answer
101 views

What security do digital signatures provide (like used when signing PDFs)?

I want to ask you one question about digital signatures as they are (for example) used when digitally signing PDFs. We know that if our document has a digital signature, we can detect if the original ...
2
votes
1answer
58 views

How are the lower levels calculated using upper levels in an optimized Merkel Hash Tree?

I was reading about the TIK protocol for thwarting wormhole attacks on adhoc networks. It uses a Merkel Hash Tree to store keys. But since the number of keys can be large, the tree is optimized by ...
0
votes
1answer
73 views

Advise key management protocol

Assume that sender and recipient both already have each others public keys(certificates). Sender needs to generate session key to encrypt some data and sends encrypted data to recipient. All offline - ...
2
votes
2answers
244 views

Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...
6
votes
1answer
249 views

What does a “cycle” mean in cryptography benchmarks?

In this table of the "Crypto++ 5.6.0 Benchmarks", for example, cryptographic algorithm performance is measured in cycles per byte for symmetric ciphers, and in cycles per operation for asymmetric ...
1
vote
1answer
144 views

what is an injective trapdoor function?

The answer to this question at Crypto.SE is clear about what a trapdoor function is, but what makes a trapdoor function "injective"?
5
votes
3answers
414 views

Perfect zero knowledge for the Schnorr protocol?

Can somebody explain (or point to a reference) why the Schnorr protocol cannot be proved zero knowledge?
3
votes
2answers
2k views

Why is AES not a Feistel cipher?

I am studying for an exam right now. And I wanted to make sure I got this point correct. AES is not a Feistel cipher because the operations in AES are not invertible. Is the above statement ...
1
vote
0answers
113 views

Career advice for our readers [closed]

I am a first year math PhD student with work experience and an MS in math. Do you have any advice regarding internships involved with cryptography and other mathematics other than the NSA? Thanks.
3
votes
1answer
541 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
176 views

How to perform benchmark of block/stream ciphers?

I would like to perform some benchmarking of different block and stream ciphers for general data (lossless and lossy data) encryption and decryption (with focus on power consumption). To get general ...
16
votes
1answer
583 views

How to provide secure “vanity” bitcoin address service?

Bitcoin addresses are RIPEMD-160 hashes of the public portion of a public/private ECDSA keypair (along with an abbreviated hash of the hash to provide a check code, as @pulpspy notes in a comment). ...
2
votes
2answers
3k views

What makes RSA secure by using prime numbers?

I am just learning about the RSA algorithm. Looking at the first two steps: Choose two distinct prime numbers $p$ and $q$. Compute $n = pq$. I have some probably stupid questions: Why do $p$ ...
1
vote
2answers
196 views

Shamir's Secret Share [duplicate]

I'm not quite sure the benefits of working over a prime modulus in Shamir's secret share- but doesn't limiting the numbers you pull from make the secret easier to guess? Instead of being over the real ...
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
158 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
561 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
631 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
511 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
213 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 ...

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