4
votes
1answer
242 views

Is PKCS #1 v1.5 RSA encryption padding secure under these conditions?

The PKCS #1 v1.5 padding scheme for RSA has been proven to have some weakness when used with TLS for example. My question is: is it still secure under the following conditions? Alice sends a ...
1
vote
0answers
44 views

Client puzzle using hash

When a server is under attack, it send the client the following data: Nonce - a byte array of Y length Hash - the hash digest of the puzzle solution The client has to find X such as ...
2
votes
1answer
142 views

Do any one-key-of-many cryptographic schemes exist?

I'm pretty sure I understand how public/private key cryptography works. Anybody can encrypt a message using a well-known public key, but only the person who holds the private key can decrypt it. My ...
0
votes
1answer
109 views

Why is DDH not hard over $\mathbb{Z}^*_p$?

Why is Diffie-Hellman key exchange not hard over $\mathbb{Z}^{*}_p$?
1
vote
1answer
87 views

Prove that two MACs with incremendal PRF application are not secure

How do I prove the following MACs are insecure?                                                        1                                                                                   2
1
vote
0answers
71 views

Parallel-resistant proof-of-work scheme without hidden knowledge

Follow-up to: Parallel-resistant proof-of-work scheme? Is there a proof-of-work scheme that: can only be solved serially; given the solution, can be verified in minimal time; deterministically ...
1
vote
1answer
102 views

Rock-paper-scissors over network, how to protect from cheating server?

I'm trying to design cryptographic protocol to play Rock-Paper-Scissors with two parties, neither trusting each other, nor trusting server they use for communication, so game is 'provably fair'. So ...
2
votes
1answer
424 views

Question regarding multiple SHA-256 rounds on a Bitcoin Brain Wallet passphrase…

I am attempting to come up with a way of memorizing a seed that could lead to any number of brain wallets for bitcoin. I need multiple wallets because a) I don't want all my eggs in one basket, and ...
1
vote
4answers
330 views

Messages exchanged between Bob Alice are encrypted safe?

Can you help me understand the following reasoning? If Alice sends Bob a message and that message is encrypted with two keys simultaneously: a symmetric key (Ks) and Bob's public key. The symmetric ...
8
votes
3answers
925 views

SHA-224 Purpose

One of the new features of Java 8 is the SHA-224 message digest. What is the use case for having a 224-bit-length hash?
1
vote
2answers
134 views

hill cipher encryption way 1x3 plaintext matrix

Can someone help me with a Hill cipher? When do I have to use: 1x3 plain text matrix (p1, p2, p3) * 3x3 key matrix 3x3 key matrix * 3x1 plain text matrix Or they are both correct? I tried to ...
1
vote
1answer
88 views

What is difference among eavesdropper attack, multiple message attack and CPA attack?

What is/are difference(s) among eavesdropper attack, multiple message attack and CPA attack in context of symmetric key encryption? I only know that in eavesdropper attack there is an adversary ...
0
votes
1answer
87 views

Hash Function to get same value for different messages [duplicate]

I am studying a function where I found the some hash properties. Hash functions: Given a code c is computationally infeasible to find m such that ...
17
votes
3answers
927 views

How secure is the Bitcoin protocol?

Are there any evidence (other than not being cracked so far) that the Bitcoin protocol is secure? "How secure" is it? (I realize that this might not qualify as a meaningful question - feel free to ...
7
votes
2answers
4k views

How does a padding oracle attack work?

I am unsure of how a padding oracle attack works. What I am not getting is how changing one bit at one time allows one to exploit(get keys) ASP.NET machines. Can anyone explain this?
2
votes
2answers
83 views

Proving a decision was randomly made [duplicate]

Alice and Bob want to agree on a bit $0$ or $1$. Both know it would be fair to pick that at random, but there's no way they could meet to throw a dice and no third party they could trust. Are there ...
3
votes
2answers
122 views

secure integer comparison

I have been going through a huge amount of papers to find a simple and a practical method to compare integer numbers without revealing their original values. I know that this falls within the area of ...
0
votes
1answer
45 views

Ensuring that an operation takes a relatively specific amount of time, but easily verify the result

I want an algorithm of some sort that can ensure that an operation takes a fairly specific amount of time, but proof that this operation was done can be completed relatively inexpensively. For ...
4
votes
1answer
155 views

Entropy when iterating cryptographic hash functions

Consider a cryptographic hash function that maps $n$-bit strings to $n$-bit strings: $$ \DeclareMathOperator{\H}{H} \DeclareMathOperator{\SHA}{SHA-256} \H(x) : \left\{0,1\right\}^{n} \mapsto ...
1
vote
1answer
133 views

Non-interactive Zero-knowledge proof signature validation without public key

I'm looking for a method for a scenario with following requirements: At least 3 people (A,B,C,...) are in a Network where they can broadcast messages to everyone but not communicate with a specific ...
2
votes
0answers
68 views

How is HMAC(message,key) more secure than Hash(key1+message+key2)

I understand how for hash functions which are vulnerable to length extension attacks (such as SHA1 and SHA2) it is safer to use a HMAC construction. What I don't understand is, how or why is ...
1
vote
0answers
73 views

RSA timing attack

Given an RSA implementation that uses Montgomery multiplications and CIOS exp algo, but NOT CRT. Given a decryption1 oracle that takes chosen cipher text and responds the plain text and the time it ...
2
votes
2answers
89 views

Soundness idea of basic zero knowledge prood

I am having a hard time figuring out the soundness proof of the bellow zero knowledge protocol. As it is a typical proof, I would love to deeply understand it. zero knowledge argument that $h \in ...
1
vote
2answers
71 views

McEliece key size

There's a lot of references about McEliece key size being the barrier for proper usage of the algorithm, exactly (or roughly) how large are the keys?
1
vote
1answer
123 views

How to solve custom made ciphers? [closed]

How would you go about solving basic custom made ciphers - e.g. one generated from this website http://www.wikihow.com/Write-a-Custom-Cipher-Carefully? This is solving it without knowing the method ...
-1
votes
1answer
30 views

In Needham Schroeder key distribution what happens if responder's part is not encrypted in step 2 with Kbs but encrypted instead by Kab in step 3

The Needham-Schroeder protocol is: 1 A→S:A,B,Na 2 S→A:{Na,B,Kab,{Kab,A}Kbs}Kas 3 A→B:{Kab,A}Kbs 4 B→A:{Nb}Kab 5 A→B:{Nb−1}Kab Here Na and Nb are nonces. Kab is the key between a and b Kas is ...
3
votes
1answer
685 views

Why is Serpent faster than AES in this benchmark?

I have a laptop without the AES-NI CPU instructions but with SSE4.1. I'm using Linux and tried the (in-memory) cryptsetup benchmark to get the rough tendency which returned: ...
1
vote
1answer
347 views

CryptoJS.AES result always has same first few bytes?

When using this very minimal CryptoJS AES example: ...
1
vote
1answer
54 views

Distinguishing Attack on CBC-MACs

I want to ask again about distinguishing attack on CBC MAC, based on the paper published by Ketting Jia, Xiaoyun Wang, Zheng Yuan, and Guangwu Xu: Distinguishing Attack and Second-Preimage Attack on ...
1
vote
0answers
34 views

McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...
-1
votes
1answer
74 views

How to create PSK key? [closed]

I'd like to create a PSK key to use with TLS-RSA-PSK-WITH-AES-256-CBC-SHA - what is the format of this key?
3
votes
1answer
95 views

Quadratic Sieve: what's the next step after it fails?

Factoring some 20-45 digit values n with a (simple) quadratic sieve, the quadratic sieve may end up with pairs of x and y s.t. $x^2 \equiv y^2 \pmod n$, but neither x+y nor x-y has a nontrivial gcd ...
-2
votes
1answer
96 views

Zero Knowledge Proof for Correctness of the product of additive ElGamal Ciphers [duplicate]

Suppose we use Additive ElGamal defined as follows: Let $(K,E,D)$ be a triple. The key-generator $K$ outputs the description of a finite multiplicative group $G$ of prime order $q$, with three ...
0
votes
2answers
200 views

Should an AES byte key generated with OpenSSL be converted to hex?

I am generating a key & iv with Ruby's OpenSSL wrapper for an AES CBC 256 setup: ...
1
vote
0answers
77 views

Public-key based on roots of polynomial

In general it's hard to calculate the roots of a given polynomial P(x). But the other way back calculating the coefficients is much easier (Vieta's formulas). If this is a one-way function, is it ...
1
vote
0answers
71 views

Does a dynamic accumulator exist yet? [closed]

I’m looking for a one-way accumulator which can safely add new members (deletion is not necessary) and does not rely on a trusted party in any way. I’ve been looking for one, I need it for this ...
3
votes
1answer
77 views

What is the importance of the $r$ and $c$ values for the Sponge Construction?

What is the importance of the $r$ and $c$ values? Keccak[r=1600,c=0] is stated on a calculator on the Keccak website to be a checksum. But I figured if c=0, then there's only one possible output? ...
1
vote
0answers
125 views

Is this a secure (and correct) sign-then-encrypt technique for transferring messages?

After reading some information on the way iMessage works I have been working on writing some code to try my hand at securely transferring messages in a similar manner and I wanted to confirm that the ...
0
votes
2answers
78 views

Subexponential algorithms for DLP in $\mathbb{Z}_s \times \mathbb{Z}_t$

Consider the accepted answer to the question: Why are elliptic curves better than cyclic groups? It seems to suggest there are subexponential algorithms (i.e., algorithms with running time $$ ...
1
vote
1answer
135 views

Is the term “Elliptic Curve Discrete Logarithm Problem” a misnomer?

I have just started studying Elliptic Curve Cryptography, and I have this doubt. In ECC the group operation is addition (and not multiplication). So, why is ECDLP stated as a variation of the discrete ...
4
votes
0answers
224 views

Odds of false error detection in a randomness test using the chi-squared test?

Common Criteria classifies the requirements for true Random Number Generators, and specifies how these should be tested against failures (these can occur accidentally, or following deliberate attack, ...
1
vote
1answer
110 views

Why concatenate the key a second time in HMAC? [duplicate]

On Wikipedia it is said that HMAC is basically (without taking into account padding): $H(key\ \Vert\ H(key\ \Vert\ message))$ where $\Vert$ denotes concatenation. I understand the need to hash ...
1
vote
1answer
121 views

Hash functions with or without secret key

The classical definition of hash functions (found in books) are OK, but when studying a little more there is a lot of notions that seem ambiguous (contradictory) to me : Sometimes we have hash ...
-1
votes
1answer
53 views

Meet in the middle attack - message and key

I clearly understand the story of Alice and Bob: Alice and Bob are going to use double DES. They know the keys K1 and K2. Alice sends to Bob the encrypted message c= EK1(EK2(m)). Bob decrypts the ...
-1
votes
1answer
140 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
4
votes
0answers
115 views

How can I create an RSA modulus for which no one knows the factors?

It's easy to create an RSA modulus where almost no one knows the factors: for example, I can generate two 1024-bit primes $p$ and $q$ and set $n=pq$. If I publish $n$, I will be the only person in ...
4
votes
1answer
340 views

What prevents a padding standard to cause a data loss?

In here different byte padding standards are listed as ANSI X.923, ISO 101.26, PKCS7, ISO/IEC 7816-4 and zero padding. All of them seems to apply padding to the last byte blocks. Odds are rare but ...
2
votes
2answers
4k views

Cipher Feedback Mode

I can't understand what CFB really is. It said in Wikipedia that CFB is same as CBC, but I find that CFB is more difficult than CBC. Can someone explain to me how CFB works. Such as how ...
-1
votes
1answer
127 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
1
vote
2answers
72 views

counter to indicate hotp count

I was trying to figure out how HOTP kept from wrapping over, when I saw this explanation of how it works, by Thomas Pornin [source]: The intended scenario is the following: the client has a ...

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