# All Questions

0answers
5 views

### Looking for zip-like file archiver with strong asymmetric encryption [migrated]

I need a mechanism that in essence locks a file so it cannot be modified. It's contents must be read-only and one must be able to view, just like an http connection, the SSL key-chain. Some kind of ...
1answer
26 views

### Key derivation function in theory & practice

I am implementing a cryptographic protocol and I'd like to generate a set of seeds using a seed for a pseudo-random function. The reason is that I can pass on only one seed and it can be used to ...
0answers
41 views

### How does hacking work exactly? [closed]

I've seen alot of posts on the web asking the same thing or "how to hack" but the answers all say that you need to know programming, this, that, etc. It's all very generic. Boiling it down to the ...
2answers
205 views

### Keyless integrity checking with SHA-256

Currently a program is loading some files from an untrustworthy source (e.g. a CDN) which could have been tampered with. It has a known SHA-256 hash of the file stored locally, then it downloads the ...
1answer
26 views

### Signing/verification between Java and the OpenSSL

I'm trying to sign/verify data between a C application and a Java application. In java for now I was using the built-in JCE provider with SHA256withRSA as ...
1answer
62 views

### How long does it take to decrypt an RSA/ECB encrypted message?

I am working on assignment where I have specific scenarios and I am little bit struggling with this one. Alice sends and email to Bob.For this e-mail, she uses the following method of encryption: ...
1answer
29 views

### Using AWS KMS with AES GCM

I am implementing client-side encryption for data stored in AWS DynamoDB, and was wondering about the correct use of AWS KMS for key management in addition to using AES/GCM. I am using the master key ...
1answer
45 views

### How to compare the efficiency of public key cryptosystems, i.e., RSA vs El Gamal?

As part of my Mathematics degree I'm taking a Discrete Mathematics module which partially covers Public Key Cryptography but does not at all enter it in depth. I'm currently working on a project that ...
0answers
14 views

### Are there any real-world E-voting systems in use with the Paillier cryptosystem?

There are a lot of theories of Paillier cryptosystem with references to e-voting. Are there any real-world E-voting systems in use with the Paillier cryptosystem?
0answers
22 views

### Are there any FHE-MPC schemes implemented?

I want to know if there are any publicly available multiparty computation schemes derived from fully homomorphic encryption schemes. An example would be the implementation of this scheme ...
2answers
336 views

### Is there a scheme where two cipher texts can be proven to have the same (unencrypted) content?

Is there a scheme where two ciphertexts (encrypted with different keys) can be proven to have the same (plaintext) content without disclosing the plaintext or any private keys? I assume that the ...
1answer
31 views

### What part of an RSA key is referred to by the number of bits? [duplicate]

When we speak about 4096- or 2048-bit RSA keys, what part of the key is this number of bits? The public key comprises both the modulus and the public exponent, and the strength of the key can also be ...
2answers
94 views

### HMAC vs ECDSA for JWT

I will be implementing JSON web tokens into my website and have a question about implementing them. I have a choice of using two algorithms, HMAC-SHA256 and ECDSA-SHA256. I have used HMAC-SHA256 in ...
1answer
245 views

### Using a SHA512 hash to encrypt data

How can I judge the level of security with the following algorithm: I create a 64 byte hash using SHA512 via some input. I use this hash to iterate over the plaintext, byte by byte, and similarly ...
2answers
52 views

### Is it OK to use a secret IV as key when creating keyed MD5 checksum for fixed-size data?

Is it OK to use a secret IV as key when creating keyed MD5 checksum for fixed-size data? Because data size is known, attacker cannot append anything. And I think it's hard to raise chosen-plaintext ...
2answers
60 views

### Securely generating auth tokens

(Disclaimer: I'm an experienced server-side Java programmer, but with little crypto experience.) Objective: I've got a login server which, given a login+password pair, should issue a unique auth ...
1answer
47 views

### Improving security of (authentication) protocol

I have a basic protocol which tries to authenticate messages going from client to server. Basically it is like this: Imagine I want to send message M to server. Client computes a MAC over the ...
0answers
156 views

### Status of Algebraic Eraser key exchange?

Algebraic Eraser™ is a relatively new asymmetric key agreement protocol (also designated the Colored Burau Key Agreement Protocol), based on a simultaneous conjugacy search problem in a braid ...
0answers
30 views

### Is this ECC based messaging method secure?

I developing an encrypted messaging for ZeroNet (aP2P file-based network, website: zeronet.io) and would like to have some guidelines if any of this could work. My first idea: In ZeroNet every user ...
0answers
6 views

### Does RekeyLimit property in sshd_config enforce Re-keying/Key re-exchange? [migrated]

I have set the RekeyLimit property in sshd_config and tried to perform a ssh. But I could not see rekeying happening in the verbose logs, all I see is the below log message at the start of the session ...
1answer
19 views

### How to prove that a SKE scheme is IND-CPA secure

There's an IND-CPA SKE scheme 1 $(\mathsf{Gen}, \mathsf{Enc}, \mathsf{Dec})$. Scheme 2 is defined as $(\mathsf{Gen}', \mathsf{Enc}', \mathsf{Dec}')$, where $\mathsf{Gen}' = \mathsf{Gen}$, ...
1answer
125 views

### Branchless AES Implementation

Imagine a branchless implementation of the AES-128 cipher. Are there any benefits over the implementation that contains branches, other than possible prevention of timing attacks? Is it even true, ...
1answer
73 views

### Is it an overkill to add external integrity check to the AES-GCM encoding?

There is a java library for android which implements integrity checking to predefined encrypting mode(which can be found here). Short class description from author page to avoid further questions ...
1answer
38 views

### Is it secure to use ciphertext feedback with RC4?

Consider the following modification of RC4 to give some "ciphertext feedback" ...
0answers
12 views

### Advantages of the general digraph trust model over the strict hierarchical model

Are there any advantages of using reverse certificates and the general digraph trust model over the strict hierarchical trust model as described here: In the digraph model each CA can generate ...
1answer
66 views

### Cracking simple RSA when just the ciphertext and one public key is known

Can someone explain to me (Or better yet, point me to a tool that does the brute forcing) how to crack a standard, simple RSA cipher (So don't bother with padding) if I know just one public key, the ...
1answer
53 views

### Symmetric encryption using RSA for random generated password

I'm fairly new to encryption, so I wanted to check the logic for a .net solution I'm working on that encrypts data between two parties. the receiving (decrypting) party will have an RSA key pair ...
1answer
46 views

### Why is Tor alone not enough to guarantee anonymity for Bitcoin?

Why is Tor alone not enough to guarantee anonymity for Bitcoin? Why do we need the constructions like Zerocoin?
1answer
64 views

### Proving collision resistance of a hash function?

Let $f$, $g$, and $h$ be hash functions that each map binary strings of length $2n$ to binary strings of length $n$. Suppose that $h(x) = f(g(x)||g(x))$. Prove that if $f$ and $g$ are collision ...
0answers
25 views

### Can I self-classify my app for mass market encryption if I let the user choose the encryption scheme? [migrated]

I am trying to get a mobile app published in the App Store. The app makes use of several standard encryption schemes (such as AES, Twofish, Serpent) provided by statically-linked OpenSSL and Crypto++ ...
0answers
36 views

### on broadcast encryption

I've read the following paper and have one question on it. M. Luby and J. Staddon, "Combinatorial Bounds for Broadcast Encryption", EUROCRYPT'98. On page 523 (12th page of the paper) the authors say ...
1answer
32 views

### Key material leak from initialized cipher?

Let's imagine that cipher (say AES256 in CBC mode) is initialized when application starts: ...
1answer
45 views

### How is a group element converted into a key?

I've only just started research on cryptography so I apologize if this is a basic question or I'm getting terms confused. I'm researching braid group cryptography and currently looking at the ...
2answers
57 views

### Leading 00 in RSA public/private key file

I found these following values ALWAYS have the leading 00 in public/private key, public key: modulus private key: modulus, p,q, d mod (p-1), d mod (q-1), coefficient e.g., modulus ...
0answers
16 views

### Strength of a cryptography algorithm [duplicate]

I'm just read this article from Atmel corporation in comparing RSA with ECC cryptography algorithms. First of all please read these two paragraphs quoted from the article: P1: Strength of an ...
1answer
32 views

### Is a hash “reset sequence” possible?

Is there such thing as "hash reset sequence" that brings hash to the same known state? A hash function has a state. In MD5 and others vulnerable to the length extension attack, the attack works by ...
1answer
66 views

### Can the Smart-Vercauteren Homomorphic Encryption be implemented as a practical fully homomorphic encryption scheme?

Smart and Vercauteren proposed a homomorphic encryption scheme (PKC 2010) following Gentry's principles. ​ Though their scheme can achieve fully homomorphism theoretically, they admitted that "for ...
1answer
37 views

### IV larger than block size of cipher?

Is there any advantage to using an IV larger than a cipher's block size? Say I'm using AES-256 in Galois Counter Mode (GCM). My file format looks like this: ...
1answer
54 views

### Consequence of a change on the Guillou-Quisquater Protocol

In the Guillou-Quisquater Protocol, the prover convinces the verifier that he knows an $e$-th root of an element $y \in \mathbb{Z}^*_n$ ($p, q, e$ are primes, $n = pq$ and $e$ is coprime with ...
2answers
81 views

### How does a Hashing algorithm always result in a digest in a fixed size?

This question revolves around the Hashing Algorithm attribute that the resulting digest is always the same size (also known as Fixed Width). For example, whether you hash the word "hello", or 10gb ...
3answers
84 views

### Factorizing N to derive D

So I have the value of N. I have to use this value of N to find the value of D. N = 265291078722948385089717069136983657793 Now I read about RSA algos and found out that ...
1answer
54 views

### Do low-entropy fingerprints actually make any sense?

I'm thinking of ZRTP and OTR in particular here. From my understanding, after a Diffie-Hellman session is initiated, the shared secret is then hashed into a 4-digit number, which the two parties can ...
2answers
54 views

### What is the use case for XOF functions (i.e. SHAKE128/256)?

FIPS 202 defines 2 functions: SHAKE128 SHAKE256 As extendable-output functions (XOFs) that can have variable output length. But in Appendix A.2 marks: it is possible to use an XOF as a hash ...
1answer
44 views

### Time complexity of trial division

Suppose $n=pq$, where p,q are prime numbers. let $p ( \le q)$ be the smallest prime, then we know that $p \le \sqrt{n}$. In trail division, we check $n \mod i$ for the values of $i$ from 2 to ...
1answer
35 views

### Help with pseudorandom functions

I started a new lecture this year about crypto and I've had a few problems in the first few weeks with the exercises we got. I would appreciate a "guide" on how to solve problems like the following ...
2answers
74 views

### Are all encryption tools made equal?

I'd like to encrypt work-related data backups stored on an external drive. The backups contain proprietary company information and trade secrets. My current backup program, Comodo Backup, allows me ...
2answers
134 views

### Is there any relation between two strings with the same MD5 hash?

Is there any relation between two strings with the same MD5 hash? For example these two strings: ...
1answer
54 views

### what problem happen if we always use IV Zero in CBC Mode? [duplicate]

i have a question about CBC operating mode. what problem happen if we always use IV Zero in CBC Mode?
0answers
36 views

### Why we use operating modes in cryptography? [duplicate]

Why we use operating modes (CBC , . . ) in cryptography? i mean what is the essential of use it ?
1answer
54 views

### Relationship between exponent and modulus in RSA (as RSA properties as listed in X.509)

In one of my assignments, I had the following question (Please read on. Not a homework assignment :) ): X.509 (1998 version) lists properties that RSA keys must satisfy to be secure. One such ...

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