# All Questions

0answers
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### Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
5answers
296 views

### Does frequent key change weaken encryption?

Following scenario: We are using OTR for communication between Alice and Bob which means after each successfull message exchange a re-keying happens for both parties leading to new AES-keys for the ...
0answers
26 views

### Implementing cryptosystems with various programming langauges

I know that most cryptosystems are currently implemented in C/C++. Has there been any effort to implement cryptosystems in programming languages such as Agda where proofs can be written about ...
1answer
37 views

### Adversarial Indistinguishability [closed]

I am trying to devise an encryption scheme such that an adversary can win the following game with probability at most $1/2 + \epsilon$. Adversary gives challenger two plaintext messages $m_1$ and ...
1answer
2k views

### DES Key Schedule Algorithm

Reading through the DES Specification it says that the keys are permuted with PC-1 initially and then shifted left both $C$ and $D$. However, before it gets ...
1answer
61 views

### Encryption Oracle Avoidance

I have a case where it may be possible for an adversary to deduce the plaintext inputs that went into creating a AES-128-GCM encrypted message (there is good IV diversity across the encrypted ...
2answers
97 views

### Discrete logarithm hash function Exercises

I have a problem with this exercise: Let $G$ be a group of order a prime $q$ and let $g, h$, be two randomly selected elements of $G$, with $g,h\ne 1$. Consider the following hash function on ...
1answer
90 views

### How is SSL secure?

if the client and the server need to exchange keys and I can sniff it, wouldn't I be able to decrypt the data transported?
2answers
632 views

### When would you increment a nonce and when not?

K is the shared key for encryption known by _Alice and _Bob. $N_A$ is a nonce created by Alice. The function f is the increment by 1 function. (1) Alice -> Bob: $E_K(N_A)$ So Alice encrypts a nonce ...
3answers
108 views

### Proving that a node is the only child

Say I have a graph of messages like this: A | B / \ C D By including the parent hash in the message to be hashed I can show that B is a child of A, ...
4answers
655 views

### Hashing a password before using for online accounts

I don't actually know what I'm talking about, so apologies if I get anything wrong. At the moment I have a password naming system for most of my online accounts that looks something like this: ...
2answers
5k views

### Predicting values from a Linear Congruential Generator

I have learnt that Linear Congruential Random Number Generators are not cryptographically secure - my understanding is that given an LCG of the form: ...
0answers
618 views

### Using RSA key pair for file encryption

I'm looking for a way to perform encrypted nightly backups of a server I administer, without storing the decryption key on the server. A form of PK encryption seems ideal for this, as I can store the ...
1answer
131 views

### chacha20-poly1305 padding and length encoding

The AEAD construction for chacha20-poly1305 described in the IETF proposal encodes message lengths into the text that is to be hashed. The newer proposal goes further and pads associated data and ...
2answers
987 views

### Why do we implement a protocol?

In general, after we design a secure cryptographic protocol and make sure that it is efficient (e.g. through complexity analysis) we implement it. Questions: Do we implement it for proof of ...
2answers
157 views

### Recommendation for lightweight algorithm for partial message encryption

I have designed a specific client and server program, which sends a file from client to server in 32k chunks. I want to encrypt only part of the data. More specifically: in each 32k chunk passing ...
4answers
1k views

### How Brittle Are LCG-Cracking Techniques?

There are published techniques for cracking LCGs, but to my eye those techniques seem very brittle — very minor changes can add nonlinearity that renders techniques like the LLL algorithm unusable. ...
1answer
69 views

### How to change the master password in a password manager

For a personal project, I'm building a password manager, based off the project in this syllabus from Stanford http://crypto.stanford.edu/~dabo/cs255/hw_and_proj/proj1.pdf Since I don't exactly have ...
1answer
46 views

### Block cipher detect padding behaviour

Suppose i have a crypto provider, i.e: i give that provider some plaintext bytes and get the encrypted result. I don't know the used encryption method, but i know ...
1answer
117 views

### Best attack on double DES followed by XOR with third key

What is the best attack here? $E_k(m)=DES_{k1}(DES_{k2}(m)) \oplus k3$
1answer
2k views

### ECDSA Compressed public key point back to uncompressed public key point

From the ECDH demo here, if I generate a private key for Alice I can get _ P = 1175846487558108474218546536054752289210804601041 Which gives the following public ...
2answers
193 views

### Secure Key exchange using javacard applet

I am working on a javacard applet project where i need... Secure communication between two applets let say there is applet A and applet B. Let say both applet has their own RSA key pairs. Now I ...
1answer
85 views

### Encryption that could have multiple decryption key

The title looks strange but it is to deal with this situation. The data we have should only be accessible by our end user and data administrators, not anyone else. Ideally, each user should have ...
1answer
102 views

### How does the Flickr length extension attack work?

I am currently reading about the length extension attack on Flickr (pdf) but not understanding what's going on there. ...
1answer
104 views

### What happens if a nonce is reused in ChaCha20-Poly1305?

In ChaCha20-Poly1305, I know that reusing a nonce loses confidentiality and integrity for all messages encrypted with the (key, nonce) pair. However, is security affected for those messages encrypted ...
1answer
94 views

### How to encrypt a number using AES?

How to do padding to input giving to encrypt using AES algorithm if the input is less than 128 bits? I need to encrypt a decimal number such as 10.
1answer
103 views

### How to generate fingerprint for PGP public key

I would like to know how to generate a fingerprint for an openPGP public key. To be clear, I'm interested in how the fingerprint is generated. I'm aware that I can get the fingerprint with a ...
1answer
92 views

### Plaintext and ciphertext block sizes

How can you determine the largest plaintext block size and smallest ciphertext size if you used RSA with $n=59768553302699443$ using an alphabet with $27$ characters?
1answer
84 views

### Degree of M and Max Sequence Length for LFSR

For the LFSR mod 2, determine the degree of m and maximum sequence length s_(i+3)≡ s_i+s_(i-2)+s_(i-4) mod 2 determine the degree of m and the maximum ...
1answer
58 views

### How does a user register his verifier at host in SRP (Secure Remote Password) protocol?

I read RFC 2945 and 5054 describing SRP, but there was no mention of registration. How should user registration happen in SRP? Is there a standard or paper describing it?
1answer
405 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 ...
1answer
84 views

### Why are obfuscators generally defined to be probabilistic algorithms, rather than deterministic ones?

One possible explanation is, randomness is not going to hurt you, so might as well use it. Also, if we are hoping to prove impossibility, it only makes the result stronger. One other explanation is ...
1answer
74 views

### Preserving Confidentiality and Integrity in a Public channel

Let's say I've got two people that are trying to talk in a public channel $A$ and $B$ and they want to preserve their confidentiality and integrity. Which cryptographic algorithm would they want to ...
1answer
68 views

### How to split up $GF(2^{128})$ into smaller fields?

I've heard that it's possible to split up $GF(2^{128})$ into copies of several smaller fields like $GF(4)$ so as to make the math easier in some cases. How do you do that? I know how it works for ...
1answer
157 views

### Understanding ransomware – What makes plain-text-attacks or brute-forcing so hard?

Say I have four files. Two are completely unencrypted, while the other two are the exact same files other than that they have been encrypted with (apparently) the same public key (via a ransomware ...
1answer
114 views

### State of the art techniques for Anonymous Authentication?

What are the state of the art techniques for Anonymous Authentication? What are the most popular ones? The problem domain I am considering is with respect to different users accessing cloud content; ...
1answer
118 views

### Are there any successful preimage attacks?

Are there any successful preimage attacks on any serious cryptographic hash algorithm or at least on serious-looking non-cryptographic hashes (like MurmurHash)?
0answers
40 views

### An MPC protocol from Elgamal is a good solution a homomorphic multiplication?

I want to compute a multiplication between many secret values and then distribute the result to everyone involved. For this, I thought about an MPC protocol built from Threshold Homomorphic Elgamal. ...
0answers
48 views

### Solving ADFGVX decoding with only ciphertext

Hi I'm new to the world of crypto and I'm trying to decode a message. I know it is encrypted using the ADFGVX cipher. I also have a ciphertext, but I have no other information given to me. My question ...
1answer
36 views

### Lagrange Coefficients & Polynomial in KP-ABE

My question is how these concepts relate in ABE. I am assuming that the attributes are used to share the master secret key and only a user with the right attributes for a particular access tree is ...
1answer
32 views

### What does this advantage statement signify?

In many Attribute Based Encryption papers I see this line... The advantage of an adversary A in this game is defined as Pr[b' = b] − 1/2. Can someone explain what it means to me? I assume it means ...
0answers
181 views

### Zero-knowledge proof for the product of additive Paillier ciphers

Suppose that Alice received the cipher values: $E(x_1), E(x_2), ..., E(x_n)$ that are encrypted using Paillier cryptosystem by $n$ entities with Bob's public key. Alice computes $E(\sum x_i)$ from ...
1answer
79 views

### Perfect Secrecy in Symmetric Key Systems

For symmetric key systems does perfect secrecy imply that all ciphers in the cipher space are equiprobable? I would think not, but I am finding it hard to come up with a counter example.
0answers
121 views

### Complexity using RSA

You encrypt a message using the RSA encryption system as $t^e \pmod n$ , where $t, e < n$ and $t$ is the numerical equivalent of the message. The message is written in a $27$-letter alphabet and is ...
0answers
84 views

### How can I implement decryption for NTRU homomorphic encryption scheme?

I have come across this paper On-the-fly multiparty computation via on-the-cloud Multikey from Fully Homomorphic Encryption by Lopez-Alt et al., where authors describe a NTRU-based homomorphic ...
0answers
104 views

### How does CTR-ESSIV work?

I'm using Wikipedia and Handbook of Applied Cryptography as references. I know that ESSIV generates an initialization vector (IV) by combining a hashed key with the sector number. However, I only see ...
0answers
42 views

### Example of Projective Coordinates

Given the affine form of coordinates $(x,y)$ such as $(5,3)$, if I want to convert $(5,3)$ to projective coordinates $(x,y,z)$, should the form of point be $(5,3,1)$? It is triplet not a point, right? ...
1answer
110 views

### A general definition for cryptocurrencies

I am trying to find the definitions to several terms related to digital currencies. Unfortunately, I am always ending up on Bitcoin-oriented pages and websites which only take Bitcoin itself into ...
1answer
87 views

### Cycling hashing in PBKDF's and their limitations in strength?

I hope this question isn't too similar to one that's already been asked. I also want to point out I know part the answer already, AFAIK: I just want some expert input on this. Let's model a hash that ...
1answer
17k views

### AES CBC mode or AES CTR mode recommended?

What are the benefits and disadvantages of CBC vs. CTR mode? Which one is more secure?

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