0
votes
1answer
55 views

Can BPS be used to encrypt a single integer, and restrict the output to a certain range?

As per specifications document, "We have the natural restriction that at least two characters must be ciphered, i.e. $b \geq 2$" where each character is represented by an integer of certain ...
-1
votes
0answers
27 views
7
votes
2answers
6k views

With OpenSSL and ECDHE, how to show the actual curve being used?

Using openssl s_client -host myserver.net -port 443 I can see the cipher negotiated is indeed using ECDHE for session key ...
0
votes
1answer
44 views

RSA algorithm private key extraction

Decrypting messages can be done by using the following formula: $$M = C^d \mod n$$ Where $M$ is the decrypted message, $C$ is the encrypted message and $d$ is the private key Theoretically ...
1
vote
1answer
98 views

Is this a good communication scheme?

I'm writing a wrapper for a chat program to allow for end-to-end encryption. I'm using Python and PyCrypto to accomplish this. I'd like to use a well known library to do this, but to my knowledge, ...
0
votes
2answers
49 views

RSA numerical questions

Let $n$ be the modular arithmetic, $p$ and $q$ the two large primes such that $n=p*q$ and $e$ the public exponent. Here they are two "simple" numerical questions: If $p = 13$ and $q = 17$, what is ...
1
vote
1answer
90 views

Difference between AES CMAC and AES HMAC?

Can someone elaborate on how 'signing' is done using AES- CMAC and AES-HMAC? HMAC Signing as I understand: Compute the HMAC( Hash the key and the input concatenated in a special way) Verification: ...
0
votes
3answers
49 views

How to calculate plaintext from modpower cipher

Let $a$ be the plaintext message, $e$ be a small prime exponent (such as 11, 13, 17 etc.), $b$ be cipher text and $n$ be a large modulo (non-prime). Suppose that: $b \equiv a^e \space mod ...
6
votes
4answers
760 views

Are there any practical ways to transfer random data securely?

The owner of the random.org service recommends that you do not use randomly generated numbers from their website in cryptographic keys. This makes sense, but it got me wondering. Is it possible to ...
2
votes
2answers
97 views

Why does the time complexity of RSA encryption and decryption depend on the size of the modulus?

I would think that the time complexity would depend on the exponent, not the number of bits in the modulus. For example, if the exponent were 5, using the "naive" method, we would perform 5 ...
1
vote
1answer
132 views

Is H'(M)=5*M + 9*H(M) mod 2^n a secure hash?

theorem: For arbitrary $i≥0$ there exists $m,n≥0$ such that $35+i=5m+9n$. We can use this theorem for constructing simple hash function. Let $M$ be message and $H(M)$ be its hashed value with ...
0
votes
0answers
10 views

A standard for multi-key provider encrypted data?

I'm looking for a standard that standardizes data encryption with multiple and diverse key sources to represent a heterogene access structure and culture. The standard must offer the following ...
3
votes
1answer
37 views

What information should I send along with an AES ciphertext and is there any standard to do that?

While using some crypto implementations I got to see that many times a comment is added to the ciphertext. For example: ...
2
votes
2answers
60 views

Theoretical security of bit rotation for encyption

This is a theoretical question. I have a idea, encryption by bit rotation in byte. Do not know if something like this already exists. General concept is: First n bytes is rotated to left or right ...
3
votes
1answer
32 views

Generating passwords from a master password using rules

I realize it's generally considered bad idea to use the same password everywhere. I can use icloud / lastpass to generate my passwords for me, but that leaves me clueless when I don't have access to ...
6
votes
2answers
115 views

Is TLS secure against VM reset attacks?

Is the TLS protocol secure against VM reset attacks? Background: Imagine running cryptographic software inside a virtual machine (VM). A VM reset attack is one where the the state of the software is ...
2
votes
1answer
82 views

Authentication protocol which detects client impersonation from another machine

Consider following authentication protocol. Client ClientA knows some initial secret KeyA shared with server. Client also knows IP of legitimate server. Now when client wants to establish connection ...
0
votes
0answers
31 views

Point Multiplication Double-And-Add-Method [migrated]

Double and Add Method If i have k=5, base poin G =(2,1) Is is double and method like this: 5.G = 2.(2G)+G How is the logic, is i want convert integer 5 to base 2, like this : 5 = 101 ...
2
votes
0answers
31 views

Are collisions in AES-128 theoretically possible when the plaintext is the same? [duplicate]

Is it theoretically possible to find $P$, $K$, and $K^\prime$ such that $E_K(P) = E_{K^\prime}(P)$ where $E$ is AES-128 and $K \ne K^\prime$? I'd imagine this would be infeasible, but is it actually ...
4
votes
2answers
100 views

Is there such a thing as a hash function with a fixed size input?

That seems like it would be a useful primitive. Using it in place of a block cipher in the Merkle–Damgård construction would give a variable-length hash, maybe without the tricky business with related ...
1
vote
1answer
92 views

S boxes in Blowfish

I know how the s-boxes in blowfish are initialized, but how is the output sorted, I mean which bit from the input goes where in the box ? and what do mean they have 256 entries if they are 32-bit ...
3
votes
1answer
53 views

How exactly does certificate based authentication work?

I know the concept of key generation, as well as encryption and decryption using public and private keys. When it comes to authenticating a user by a server, in general there are three types: ...
0
votes
0answers
38 views

When we use permutation and random long sting to hide a message

This question is modified version of this: Can we use merely permutation to hide a message? I have an English name $m=m_1 || m_2 ||..||m_{30}$. I pick a random string $d=d_1 ||..||d_{70}$ I mix ...
3
votes
1answer
711 views

Is this DIY remote lock protocol secure?

I need your advice on following scheme of exchange protocol between remote lock and key. I'm planning to use following algorithm: Key generates unique value that never repeats (in reality it's just ...
11
votes
2answers
268 views

How to determine the order of an elliptic curve group from its parameters?

Let $\quad E:\; y^2 = x^3 + ax + b \quad$ be an elliptic curve defined over a finite field $\mathbb F_q$ where $q = p^n$, $a,b \in \mathbb F_q$ and $p \neq 2, 3$. By Hasse's theorem we know that the ...
-1
votes
1answer
29 views

Security for secret key of server in Identity-based Encryption

In the key set up phase, server generates Pub=s.P, where s is the secret key.Then , it gives clients Pub,P as public parameters and pairing descriptions. Is it possible for clients to pre-compute r.P ...
2
votes
1answer
168 views

Simple digital signature example that one could compute without a computer?

I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms. There is a great question ...
3
votes
1answer
32 views

Is it okay to send an encrypted key using XSalsa20-Poly1305, and send subsequent messages using ChaCha20-Poly1305?

I am looking at a cryptographic protocol in a somewhat unusual environment: the communicating parties can share arbitrarily long secret keys over a secure channel. If forward secrecy is not required, ...
2
votes
1answer
85 views

Encrypting passwords

I am using Android's keystore to generate a key which is protected by fingerprint authentication. This key can be used to encrypt any secrets. In my case, I want to encrypt a user password (which is ...
3
votes
2answers
53 views

Should the most significant byte of a cryptograhic key be nonzero?

Is it safer to give a non zero value to the most significant byte (MSB) of a cryptographic key to ensure its length (not 31 instead of 32 for an EC private key on a 256-bit curve for example)? Or is ...
0
votes
3answers
82 views

How to convert RSA public keys to one key to use for text hashing?

I've recently asked a question about RSA encryption. One of the things that I don't understand is the usage of two public keys. In the example on Wikipedia, a message is encrypted like: ...
0
votes
0answers
47 views

Why doesn't Morse Code try to achieve more compression? [migrated]

I was working on the Morse Code article (wikipedia), when I noticed something strange. There might be a reason, but I can't find it. As you can see, the code symbol ...
10
votes
3answers
145 views

Are there reasonably secure online voting implementations e.g. for student council elections?

Assume a university want to elect the student council. This was done via paper ballot and there is a need to reach more students for voting, so electronic voting is on the table. While researching ...
-1
votes
1answer
79 views

Can we use merely permutation to hide a message?

This question is related to this: When all shares of a secret are given to adversary as a permuted matrix I think the below question is a simplified version of that. Assume we have a 40-bit ...
4
votes
3answers
330 views

Parallel-resistant proof-of-work scheme?

I am looking for a proof-of-work scheme which cannot be effectively parallelized. For example, in hashcash (and by extension bitcoin) you have some collision-resistant hash function $f()$, a target ...
1
vote
0answers
41 views

Vulnerabilities in SHA-1 [duplicate]

Are there any known vulnerabilities in SHA-1 that can be exploited? Certain patterns that it shows? I recently performed a frequency analysis using 20,000 common words, and found nothing exploitable. ...
5
votes
1answer
150 views

Hamiltonian Path Zero Knowledge Proof using Commitments to a Series of Edges

Commonly, Zero Knowledge Proofs based on the Hamiltonian Path or Cycle problems are given as follows: The Prover has a graph $G$, for which he knows a Hamiltonian Path (or Cycle). $G$ is also known ...
1
vote
1answer
21 views

Do any Identity-based Encryption Systems support messaging between domains?

Identity Based Encryption is covered under RFC 5091 (specifying the algorithm), 5408 (specifying data structures), and 5409 (using IBE with Cryptographic Message Syntax). However, every IBE ...
0
votes
1answer
48 views

RSA-OAEP: How does it work?

I was looking at this image about OAEP: ..and was wondering what was happening here. 1) We have a data block DB which consists of: ...
6
votes
1answer
149 views

Why $e>n^{3/2}$ prevents Wiener's attack

Here's the Wiener's attack as I understand it. Suppose $n=pq$ with $q < p < 2q$, and $d < n^{1/4}/3$ where $ed=k\phi(n)+1$ and $e < \phi(n)$. $$\begin{align*} n-\phi(n) ...
0
votes
1answer
41 views

Understanding the distinguisher for a PRG

Given the following definition of a psuedorandom generator, I'm having trouble understanding what exactly the "distinguisher" D is outputting, and when?
2
votes
0answers
54 views

Q: Relevance of physical layer security to cryptography

I found that there are quite some active research activities in a field named "physical layer security", with in particular some types of codes that apparently are different from those commonly ...
1
vote
2answers
43 views

Stateless proof-of-work system with 0-roundtrip time

I'm designing an API. To avoid abuse, I need to rate limit the requests somehow, but I don't want to do it per user as it's very easy to create new accounts automatically. I think a proof of work ...
1
vote
0answers
40 views

Compressing AES [duplicate]

I have this program which encrypts multiple files using AES then compress it using LZO into one single file. The problem is that the final file is almost equal in size than all the files which means ...
0
votes
0answers
28 views

Subset sum hardness

Hardness of a subset sum probleme depends on it's density. Is it possible for a subset sum problem to be intractable even if it's density is less than 0.9408 ?
4
votes
1answer
198 views

What is the “compression function” in Merkle-Damgård?

Is the "compression function" in Merkle-Damgård just a collision-resistant, one-way hash function but one that operates only on fixed size inputs? If so, is MD just a way to extend it to work on ...
0
votes
1answer
51 views

Finding a secret cipher given the key and known plaintext?

Let $x,y,k$ be plain text, cipher text and key respectively. Also suppose $\operatorname{Enc}$ is the algorithm of encryption for block cipher with size $n$. So we have $$\operatorname{Enc}_k(x)=y$$ ...
1
vote
0answers
19 views

Security issues with self encryption? [duplicate]

I'm thinking about the scenario of using a set of (potentially untrusted) hosts to store (potentially private) files. Think something like distributed backup where you contribute some disk space and ...
0
votes
0answers
23 views

Degrade in performance with SSL_OP_SINGLE_ECDH_USE?

We have used SSL_OP_SINGLE_ECDH_USE when setting up our SSL_CTX . This seems to be causing a degrade in performance. I'm not able to find proper documentation for it except that it generates new ...
0
votes
1answer
23 views

Proof of Knowledge/Data Integrity using Hash Function

Objective: A verifier wants to ensure that a block of data M is also known to a prover. The protocol should exchange little information and should not leak information about the value of M. Proposed ...

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