1
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1answer
128 views

What is meant by this notation in the ElGamal key generation process?

Alice chooses i) A large prime $p_A$ (say 200 to 300 digits) ii) A primitive element $\alpha_A$ modulo $p_A$, iii) A (possibly random) integer $d_A$ with $2 \le d_A \le p_A-2$. Alice ...
1
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1answer
316 views

Is symmetric key encrypted with server's public key secure

I'm trying to implement lightweight yet secure protocol for communicating two trusted parties with each other. Consider following scheme: Alice wants to establish secure two-sided channel with ...
1
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1answer
123 views

How can I split a message in parts of similar size or smaller?

I have a 130-160 characters message that I need to split in say, 3 parts, and be able to reconstruct it by recovering all 3 parts. I also need that these parts are type-able, meaning that they can't ...
1
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1answer
140 views

Do I need to keep a 64-bit version number secret?

Assume the following structure: version | iv | ciphertext | HMAC(version | iv | ciphertext | ..., key) The version starts out ...
1
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1answer
324 views

Polynomial multiplication and division in2^128

I want to multiply and divide polynomials, and implement the extended Euclidean algorithm for polynomial greatest common divisors, over a Galois Field of size $2^{128}$. Moreover, I want to use the ...
1
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1answer
305 views

Security of Salsa20 with some known plaintext?

Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known? Assume that a different IV and Key are generated before each file is ...
1
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1answer
260 views

chaining rsa with ecies

In an answer to a previous question it was suggested that one way to protect your asymmetrically encrypted AES-256 keys, from say a solution to prime factorization, would be to chain asymmetric ...
1
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2answers
199 views

standard way to authenticate parties with public keys without certificates

Is there some standard protocol for mutual authentication of two parties when there is possibility to use public key cryptography? The problem is that two parties can use public key cryptography but ...
1
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1answer
220 views

Password verification

I'm looking for feedback on whether or not this is the proper way to approach password verification without transmitting the actual password. Are there any problems with this scheme. We are working ...
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2answers
437 views

Using salted hash as password for easy memorization without reuse?

I had an idea earlier: Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example: ...
1
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1answer
115 views

What's the difference between “HashX-512” and “HashX-1024”?

I need to make a Skein hash's, specifically, Skein-1024; however, I only have access currently to Skein-512. Is there any way to utilize a Skein-512 function to get the result of a Skein-1024 hash? ...
1
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1answer
163 views

which asymmetric cipher provide highest performance?

to get highest performance Which asymmetric cipher provide fastest encryption/decryption ? ECC or DH ? what key size is recommended today ?
1
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1answer
130 views

In which disciplinary category can cryptography be put?

Is it a multi-disciplinary, inter-disciplinary, cross-disciplinary, or maybe even trans-disciplinary? What are the basis to describe each kind? I mean, how can we infer by which disciplinary field we ...
1
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1answer
333 views

What is total key space in transposition algorithms

How we can measure key space in transposition algorithms? Should we specify the method, like rail fence?
1
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1answer
471 views

Partial decryption of large file in AES-GCM (or other modes)?

Lets assume a 4gig file that is internally made of 1 million pages of 4k bytes each (page). the file was originally AES-GCM encrypted these pages (or entire file) lives across the internet i.e. ...
1
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2answers
2k views

is AES secure for java application licensing

I have to license a java application and want to code a quick implementation, the scheme I came up with is: 1) The Application calculates a string X which we assume to be the md5 sum of the ...
1
vote
1answer
178 views

How to solve the reverse of an equation that uses MOD?

I've been tasked with reverse engineering an unknown crypto function. The function uses the following constants: $a=380951$: I noticed that this is a prime number $b=3182$: I noted that this is a ...
1
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4answers
343 views

Bad/Crackable Encryption Example?

I've been tasked with building up some security exercises (basic CTF training kind of stuff) for work. This should contain a bit of crypto, but my knowledge in this space has been limited to using the ...
1
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2answers
358 views

AES encryption with shared IV

Sorry about the horrible title, didn't now what to say. I'm trying to avoid having to send an IV with every message purely to keep packet sizes down, so I thought of a method to establish a "IV ...
1
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1answer
222 views

Scrypt as a KDF with one-time high-entropy input

I'm looking at using Scrypt as a KDF. Assume the following: the input will always be high-entropy random bytes generated by a CSPRNG the length of the input can vary from between 8 to 32 bytes the ...
1
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1answer
1k views

Use of CBC-AES-256 to encrypt usernames

I came across some code in our project that encrypts usernames (limited to 50 chars, most are less than 10) using the following parameters: IV size is 16 bytes Key size is 32 bytes Algorithm is ...
1
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1answer
304 views

brute force attack on KDF vs KEY

if we believe 256bit keys are secure in AES against any brute force attack, is that possible we use a KDF (convert user's weak entered password in truecrypt into a fixed AES key) with too much round ...
1
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3answers
2k views

How to check the strength of an encryption algorithm?

I asking for advice on how to check strength of an encryption algorithm.
1
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1answer
997 views

AES CBC with fixed or predictable IV, what are the risks?

I am making a call with parameters from application "A" to a web application "B". Parameters are in the query string of the URL. They don't need to be hidden. But I want to be sure that nobody can ...
1
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1answer
113 views

Question about use of IV in this cipher

Main cipher objective : Generate a keyed CSPRN stream, that does not expose useful information about the state of the CSPRNG, and xor this with the plaintext. To prevent an attacked who could somehow ...
1
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1answer
4k views

How do I derive the time complexity of encryption and decryption based on modular arithmetic?

I want to calculate the time complexity of two encryption and decryption algorithms. The first one (RSA-like) has the encryption $$ C := M^e \bmod N $$ and decryption $$ M_P := C^d \bmod N. $$ ...
1
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1answer
110 views

Two files encrypted with related data versus one file

I have some code that takes a list of credit-card numbers, splits the number into two chunks, one chunk is 8 characters long, the other chunk is the remainder. Each series of chunks is saved into ...
1
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1answer
137 views

How does this Cesar Cipher work?

Suppose I have this cryptogram: http://pastebin.com/QpfRMBg1 Clearly it's a Ceasar Cipher which decrypts to: http://pastebin.com/r50heZuU with a simple shift of 10... OKay, no big deal. Let's take a ...
1
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1answer
291 views

Can Add and Multiply On Cipher Text achieve all operations?

A Fully homomorphic encryption scheme needs to support an evaluate function that can do add and multiply operations on cipher text. Can we do all kinds of complex operations on cipher text like ...
1
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1answer
88 views

Is there a big RSA Data Set

Is there a big dataset containing RSA public $(n,e)$ and private keys $d$ and primes $p,q$ where $n = p.q$ ?
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3answers
320 views

Deterministic key generation

In a situation where it is required to generate n number of keys deterministically from a single piece of seed information can we assume that b breached number of keys, no matter what the quantity ...
1
vote
1answer
166 views

On the fly key generation for cloud storage objects

Cryptographic key management involves storing and managing encryption decryption keys , certificates , signatures etc . If the requirement is just to store and manage object specific keys ( say ...
1
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1answer
187 views

Crack cryptographic hash functions using Toffoli gates?

Might it be possible that reversible combinatorial circuits (or some emulating software) are going to be used to get the input of the white box? I mean if I have constructed a proper reversible ...
1
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2answers
413 views

Finding partial pre-image of MD5 hash

I have the following requirement for hashing using MD5. H(A,B,C,X); Where values A,B & C are given. However X is not given. I would like to find out what value of X would give a hash beginning ...
1
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2answers
365 views

ECM Implementation is really slow

I followed the algorithms 14.4 (computes 1st and 3rd coordinates in (X,Y,Z)#k modulo n) and 14.5 (factorization using ECM) in David Bressoud's book 'Factorization and Primality Testing'. I think the ...
1
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1answer
1k views

AES encryption for images [closed]

Why AES based encryption is not recommended for encrypting images with high redundancy in their content? for example, the encryption of an image which shows a bird in the blue sky. Most of the pixels ...
1
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1answer
297 views

How is block cipher padding verified for consistancy?

Under what circumstances is a decryption routine able to tell that the padding of a message is invalid? If a cipher text block where to be randomly modified, what is the probability that the padding ...
1
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1answer
697 views

RSA 1024bit decryption performance

i want to know how many RSA 1024 bit long key decryption can a regular pentium4 computer do per second ? how to calculate RSA performance and determine its remaining time ?
1
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1answer
127 views

MD5 pre-fixing with an unkown postfix

Is the MD5 prefixing attack still valuable to an attacker if he doesn't know the postfix of the string? For instance, what if the following sanity check was being used: ...
1
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1answer
159 views

Trying to find an algorithm to share portions of a key with multiple people

Sorry if this question's a bit basic, but I don't know of any way to ask it concisely enough for a search... What I'm looking for is a proven means of doing the following: Create x number of ...
1
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1answer
186 views

Probability of Repeated Encrypted Block In Output Feedback (OFB) Mode

Is there any probability/chances of repeated encrypted block in Output Feedback (OFB) mode? Is there any existing documentation/studies about that? If it is existing, can you please provide me a link ...
1
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2answers
165 views

Can you distinguish encryption methods from the output?

Suppose that you see all IP communication packets between two computers for a day, as they pass through a connecting router, and this amounts to 10MB. You additionally know that all data transmission ...
1
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1answer
1k views

How can 3DES encryption use decryption in the middle step?

I have been reading about the 3DES algorithm and I cannot understand one part. In 3DES we do following operation: $$C=E[K_3,D[K_2,E[K_1,P]]].$$ Where $C$ is ciphertext, $P$ is plaintext, $E$ is DES ...
1
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1answer
77 views

Cryptographic Algorithm/Protocol needed

I am trying to achieve the following: Encrypted files are stored on users filesystem. The user uses my client to authenticate against a server. Once he is authenticated successfully he gets a token ...
1
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2answers
96 views

Encrypting documents through a proxy key

Suppose I'm developing an app to secure a lot of documents. These documents were encrypted (say, using AES) with a key X. This key X is basically the password that the user enters before wanting to ...
1
vote
1answer
437 views

Existing dictionaries of popular words to help solve a random substitution cipher?

I'm trying to find faster ways to solve this: http://cryptogram.org/solve_cipher.html Actually lists of common words are good, but they are often limited to 1000 words. I found this, but I'm not ...
1
vote
2answers
737 views

Finding the LFSR and connection polynomial for binary sequence. [closed]

I have written a C implementation of the Berlekamp-Massey algorithm to work on finite fields of size any prime. It works on most input, except for the following binary GF(2) sequence: $0110010101101$ ...
1
vote
1answer
59 views

Proving item association without revealing one of the associated items

I'm a total noob when it comes to cryptography but I believe this falls under the "zero knowledge" category. I have two associated pieces of information: tag — known by both parties. Unique per ...
1
vote
2answers
309 views

My custom handshake

I am a beginner in cryptography and I designed a custom handshake between 2 entities $\rm C$ (client) and $\rm S$ (server) which should meet the following requirements: Requirements: The handshake ...
1
vote
1answer
174 views

ID-Secret Scheme

I have an ID-Secret scheme and I'd like to hear if there are any vulnerabilities present. Party 1 and Party 2 hold some credentials, an ID and a Secret. Party 1 Creates this message: ...

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