0
votes
0answers
42 views

trying to get calculator and RSA calculatin does not make sense [duplicate]

got two question, I am novice in the area of crypto and currently in big learning curve. From crypto book I am going over with, I see the RSA algorithm example as follows: it chose two rand #-s: p=...
2
votes
1answer
132 views

Format preserving encryption FFX

In FFX mode the format of the ciphertext is same as plaintext. How does it ensure data integrity and authentication? Is there any bit flip attack in FFX mode? Is it malleable?
4
votes
1answer
246 views

AES as Integer Program

I read that AES can be broken by solving a Linear Integer Program (IP). From a given encrypted text, how can one construct this IP? How big is the system?
7
votes
1answer
490 views

The difference between MAC algorithms and what to use

I've been looking into message authentication codes and found several ways to create integrity for a message. I know of the following algorithms: HMAC, this can use any cryptograhpic hash function ...
2
votes
0answers
129 views

Simplicity and precision in cryptography papers [closed]

I know a PhD student who recently had his paper on applied cryptography rejected because one the reviewers claimed that it was "the solution was too simple and the notation used was more than ...
2
votes
0answers
66 views

Energy necessary for brute-forcing or decryption

I am trying to understand how the physical limits of computation apply to crytography, and came up with the scenario below as a sort of gedanken. I would be grateful to see how others answer it. ...
0
votes
0answers
49 views

Decypting a Stream Cipher

I am trying to decrypt a stream cipher. I know what the first word of the message is when decrypted but I am unsure how to decrpyt the rest of the message. I know what the first word is because I ...
0
votes
1answer
80 views

Is it a bad idea to use PGP encryption for structured/predictable data?

I'm working on an app and need to encrypt some structured data. The data will be turned into a string form (JSON) before getting encrypted. The data format I'm using will always start with a ...
12
votes
2answers
2k views

If you hashed a hash an infinite number of times would you end up with a unique hash?

If you took a hashing algorithm for example MD5 and repeatedly passed the output hash back into the algorithm an arbitrarily large number of times would you eventually end up with one unique hash? My ...
1
vote
2answers
178 views

Can I use the output from a DRBG directly as K for AES, or do I need to use a key generator algorithm?

NIST has 3 validated "Recommendation for Random Number Generation Using Deterministic Random Bit Generators" (DRBG's) that are based on NIST SP 800-90A: Hash_DRBG (based on hash functions) ...
0
votes
1answer
81 views

How to select a 'tweak' used in FE1 mode format preserving encryption?

I'm experimenting with this library Botan which includes a module for format preserving encryption based on FE1 mode. The parameters for the Encrypt method are as follows ...
1
vote
3answers
333 views

Block cipher does not provide security by itself

What is this statement all about? When I look at a block cipher it seems pretty hard to break it and the mathematics behind insure a good complexity. It may refer to key generation, initialization ...
3
votes
2answers
387 views

Key space vs Cardinality of 1024-bit RSA

I have been trying to figure out the encryption key space, and cardinality of 1024-bit RSA. From my understanding, the key generated from 1024-bit will be primes greater than $2^{1023}$ but less than $...
0
votes
2answers
147 views

SHA-512 partial preimage

I was looking at how SHA-512 works, and I have a question. Imagine I want an input $N$ of 512 bits whose hash in hexadecimal starts with the digits 12345678. How ...
3
votes
1answer
146 views

Is it safe to derive two different keys with the same password and key derivation function using two different salts?

I would like to know if the following process would harm the security of a fictional system if the persisted data would be stolen: in this system a user has a single password. The password will be ...
0
votes
0answers
69 views

If a DES key correctly decrypts one message, what's the probability it's the real key?

Suppose an adversary gets a message-ciphertext pair $(M,C)$, where $C=DES_K(M)$. They do an exhaustive key reach to locate the lexicographically first key $T$ for which $C=DES_T(M)$. What's the ...
5
votes
4answers
7k views

Is it fair to assume that SHA1 collisions won't occur on a set of <100k strings

I'm building a system that has to take file paths, and generate a unique name for each one. I'm planning on using SHA1 as the hash function. My question is: do I have to deal with possible collisions ...
1
vote
1answer
117 views

Reducing the keyspace for a brute force attack on a chained 64-bit xor

I have a block of data which I know is encrypted using a chained 64-bit xor (sorry if that makes no sense, I'm not familiar with crypto lingo). I know a little bit about what the plaintext should look ...
5
votes
3answers
476 views

What do $0^n$ and $1^n$ mean in cryptography?

Let $f$ = $\{f_k\}$ be a pseudorandom function family. Let $G(x)$ be a pseudo-random generator such that: $G(x) = f_x(0^k)f_x(1^k)$ where $k=|x|$. I don't understand the meaning of $1^n$ and ...
0
votes
0answers
48 views

What crypto scheme should I use on embedded m2m system with assymetric uplink/downlink bandwidth?

I am working on implementing info security into custom m2m radiolink communication system, which has some restrictions: MCU based endpoint can transmit to gateway with packets max 16 bytes long, and ...
0
votes
1answer
65 views

Decrypting DES - limited information

I have a list of DES encrypted strings/data, they come in two lengths, 32 chars hex (16 bytes) or - I believe - 64 chars. I know the key, which is 8 ascii chars (I might add that I am the rightful ...
0
votes
3answers
76 views

FIPS 113 Computer Data Authentication

on the NIST website for Message authentication There is a mention of 2 approved algorithms, i am curious about the first one. the link to FIPS 113, Computer Data Authentication appears to be dead ...
1
vote
2answers
515 views

What are words in a HASH algorithms

From wikipedia: "They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words." In this context what do they mean with words? is it the same as a 32 bit (or 64 bit) block ...
0
votes
0answers
38 views

Registration and log in through public key cryptography?

I read about zero knowledge proofs. Let's say you want to create an account at a website. You choose a password $p$ and from $p$ you derive deterministically a public & private key pair $(e,d)$ ...
0
votes
0answers
157 views

What can cause similar MD5 hashes

I have a set of MD5 hashes with huge similarities in the second half of the hash, (made up) examples: ...
1
vote
0answers
80 views

Why does the ElGamal signature have the specific form that it does?

In the original paper, ElGamal(1985) starts his discussion of signatures by saying: "The signature ..... is chosen such that the equation: $\alpha^m = y^r r^s \text{mod p}$ (equation 3 from the ...
0
votes
0answers
80 views

arithmetic calculation problem to quadratic arithmetic program

I am reading the Pinocchio paper (verifiable computation): http://research.microsoft.com/pubs/180286/pinocchio.pdf The paper is rather hard for me. I am considering this calculation problem: $(c_1*...
1
vote
1answer
209 views

Zero knowledge / proof of knowledge sudoku solution

I recently started a coursera course "cryptography 1" provided by Stanford university. In one point when explaining zero proof knowledge the instructor mentions the following: Almost any puzzle ...
5
votes
3answers
612 views

Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?

One issue that private BitTorrent trackers that track users' share ratios often run into is how to keep track of people who are screwing with their upload statistics, something known as "stat-hacking"....
1
vote
2answers
125 views

How to attack the Two Time Pad?

I encrypt 2 random keys with the same 'one' time pad. You can get both encrypted keys. You don't know anything besides the size. Is there a way to attack the two time pad in this scenario? And what ...
0
votes
2answers
99 views

Looking for encryption algorithm not subject to known-plaintext attack with IV reuse

I've encountered an interesting problem where we can basically say the following: We need to encrypt messages, but we have no room to store IVs. We can synthesize IVs; however an attacker would be ...
0
votes
1answer
70 views

Adding a Random component to CBC MAC in order to enlarge the tag space

CBC MAC that is using AES as the underlying block cipher, has tag space of 2^128. If we add a random single block, concatenating it with the tag, and encrypt it again in AES CBC mode, with additional ...
1
vote
1answer
97 views

Why Might XOR's Lead to Hash Functions Lacking 2nd Pre-image Resistance?

My hash function is as follows: Cut the string in half (assume even length of 2m) XOR's the two halves together Take the result of the XOR and pass it to a function (a one-to-one and "onto" function)...
2
votes
1answer
210 views

Encryption of plain text using stream cipher algorithm

We know that in stream cipher algorithms plain text and generated key are Xored byte by byte. Generated key depends on how much plain text there is and on that basis key will generate and plain text ...
2
votes
0answers
72 views

Matsui's Linear attack on DES P box

I'm trying to understand Matsui's linear attack on DES and I have something I don't understand in his paper. In his paper he say that: $NS_{5}(16,15)=12$ (which is OK) and from that he say that: $X[...
1
vote
1answer
152 views

Permuted vectors

Consider we have two vectors $v_1, v_2$ of size $n$, and each vector contains $n$ elements. We permute the vectors as: $\pi (k_1,v_1), \pi (k_2,v_2)$. Where $\pi (k_i,v)$ denotes a permutation of a ...
1
vote
2answers
90 views

Is a padding oracle attack possible if data is only encrypted internally on a server (e.g. for storage)?

I read something about the padding oracle attack when analysing the use of an AES-encryption of data in a database and was "scared" it could be a serious issue. But after investigating a bit further, ...
2
votes
1answer
105 views

How do revocation certificates work in PGP?

I've already read how to build and upload them, but I'm wondering how revocation certificates work, what informations they hold and so on. Suppose my private key is compromised, but I have a ...
1
vote
1answer
79 views

Bilinear map + commitment

Let $\mathbb{G}_1,\mathbb{G}_2,\mathbb{G}_T$ be yclic group of the same order and $ e: \mathbb{G}_1 \times \mathbb{G}_2\rightarrow \mathbb{G}_T$, such that $u\in \mathbb{G}_1, g \in \mathbb{G}_2, a,b,...
7
votes
1answer
147 views

Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?

A 2DES like cipher $c=E^{(2)}_{K_2}(E^{(1)}_{K_1}(p))$ where both halves have an $n$ bit key is vulnerable to a meet-in-the-middle attack. Meet-in-the-middle using a big table Create a table ...
0
votes
3answers
136 views

Is the Salsa20/ChaCha20 keystream generation one-way?

Is it possible to recompute the Salsa20 or ChaCha20 key in a realistic time if the keystream and the nonce are given to an attacker? Or is the keystream generation one-way, like a cryptographic has ...
1
vote
3answers
58 views

Question about decryption

I have a question about decryption. Let's say I have a bunch of files that are encrypted. Someone gains access to those files, and finds out that he already has one of them, unencrypted. My question ...
-1
votes
1answer
66 views

Are more S boxes more secure in a SP-Network?

The classic DES uses 8 different fixed S boxes. If computer memory was not an issue, would say 800 different S boxes be more secure? I'm thinking of a SP-network that would only run on a server like ...
3
votes
1answer
125 views

Paillier cryptosystem preserve ordering of sums for two integer sequences

According to Paillier cryptosystem the product of two ciphertexts will decrypt to the sum of their corresponding plaintexts. I have two separate integer sequences X and Y that have same number of ...
1
vote
1answer
75 views

Rabin-Williams, blinding and size of Integer r?

I was reading the paper Breaking the Rabin-Williams digital signature system implementation in the Crypto++ library. The library uses blinding, but it was not enough to stop key recovery. But my ...
5
votes
1answer
339 views

Non adjacent form of an integer is unique

I have tried to look up the proof for NAF (Non-adjacent form) being unique for every integer, but as far as I have seen, textbooks only mention it as a property of NAF, but no proof is given. Also I ...
2
votes
1answer
45 views

Use of Lamport's Signature as a primitive

Is Lamport's One Time Signature used as a primitive to construct any other cryptographic protocols?
4
votes
2answers
461 views

Does SRP reduce to DH key exchange when shared password is not secret?

I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later. I ...
2
votes
1answer
179 views

Asymmetric cipher with multiple public keys

Asymmetric cryptography is well known. You generate a private key. Using the private key you generate a public key. Then you can sign a message with the private key and check signatures using the ...
3
votes
4answers
471 views

Password length versus hash length?

If a system hashes passwords with a 256-bit long hash, are passwords (which are not necessarily alphanumeric, can be any value per byte (0-255)) longer than 32 bytes useless under the context in which ...

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