6
votes
2answers
81 views

How to propagate error in variable-sized message?

I want to design a scheme to encrypt a variable-length message with a secret key, to provide confidentiality. The message is a short human-readable text string with byte granularity, let's say under ...
1
vote
1answer
172 views

How to determine the RSA Private key size from the Public.key file?

Question: How to determine the RSA Private key size from the Public.key file? Just roughly, how big it could be? ...
3
votes
3answers
95 views

Authenticate ephemeral key exchange

At the moment I'm designing a crytosystem for a VPN server. One of the requirements is Perfect Forward Secrecy, but I'n not sure how to implement authentication on the ephemeral key exchange. If both ...
1
vote
1answer
44 views

Security of a signature scheme based on both factoring and discrete logarithms

I have seen this paper: A New Signature Scheme Based on Multiple Hard Number Theoretic Problems by Ismail and Tahat: In this paper, we propose a new signature scheme based on two hard number ...
6
votes
1answer
209 views

How is OID 2a 86 48 86 f7 0d parsed as 1.2.840.113549?

I saw that an RSA key, created by OpenSSL, contains the following HEX string: 2a 86 48 86 f7 0d 01 01 01 that HEX string gets interpreted as Object ID: 1.2.840.113549.1.1.1 It is obvious ...
1
vote
2answers
273 views

Basic Encryption and Decryption related question

I recently started studying cryptography and got interested in the subject. But I got this doubt when I was studying the encryption scheme. Even though we encrypt our message and change it into ...
0
votes
1answer
59 views

What are the first 4 and last 2 bytes in DH parameter files?

when we generate DH parameters file in PEM format, like this: ...
3
votes
2answers
68 views

Hiding identifying data while allowing matching?

I do research with people about their illegal drug use, and for one project I'm doing surveys with them when they visit a needle exchange. So over time the same people get repeatedly surveyed as they ...
1
vote
0answers
22 views

Is there a system where I can securely store a secret value and compare a semi-ambiguous input to it?

I have an idea for a new kind of mobile phone lock screen. When you first create your pattern, you put together a series of colors and compass directions from the following choices: Red, Blue, Yellow, ...
3
votes
1answer
222 views

Encrypt with one cipher and decrypt with a different cipher?

I recently installed an android app called Secret Space Encryptor and think I found a serious flaw in it. Let me explain: This app provides a variety of different ciphers to use and I used Threefish ...
0
votes
1answer
23 views

Lower defree annihilator of function

Suppose $f=x_0x_2(x_1+1)+x_1x_3(x_0+1)$, annihilator is such function $g$, so that $gf=0$ for all $x$ Intuitively solution(for some reason) is obvious - $g=x_0x_1$, which holds true. (Cloud sagemath ...
0
votes
0answers
29 views

Is it bad practice to use the message digest of the plaintext as the initialization vector? [duplicate]

Data is being encrypted in a database. A message digest is being created for deduplication purposes. Is it ok to use the message digest that will be the key of the table that houses the encrypted ...
0
votes
0answers
213 views

Simple two round feistel chiffre

I am currently learning for a exam in cryptgraphy. I now try to understand the Feistel Cipher with two rounds. I do not have any information on what the functions are actually doing. The following ...
1
vote
0answers
55 views

2 round GOST_28147-89 cipher distinguisher

So, here is the scheme of how this will look graphically: The deal is to present distinguisher for this cipher. First of all here is my drafts: Way 1 Assume that distinguisher displays in ...
2
votes
2answers
110 views

Why is ECIES complex?

Wouldn't encrypting a message with AES, then encrypting the (randomly generated) AES key and IV with the EC public key suffice? What attack vectors does ECIES protect against, that an ...
0
votes
1answer
152 views

1024 RSA Hash Signature attack. Forge a valid signature

I have an RSA signature of 1024 bit where i know the following: Public modulus N Public exponent (0x03) Cypher message Summary: An MD5 hash is calculated from a collection of byte and is used as ...
5
votes
1answer
167 views

Fast 128-bit MAC with second preimage resistance?

I have an application that needs a fast 128-bit MAC to guarantee message authenticity in a protocol. I would like to reuse this MAC value as a binding identifier, so that even those who know the key ...
2
votes
2answers
279 views

Definition of authenticity

I came across various definitions of what authenticity means in cryptography. I would like to know which one is correct. The first definition - the one I always used - is the following: Data ...
2
votes
1answer
83 views

Crypto-period for keys used in PRF

I am wondering about the crypto-period for keys used in pseudo-random functions. For example, let's say I am using HMAC-SHA256 with a secret key $K$. After how many computes do I have to update $K$? ...
1
vote
1answer
157 views

Implement AES with 16 bit block size?

Can we implement AES with 16 bit block size ?if so what are its advantages and disadvantages?Is there any rule AES has to be implemented with 128,192,256 ?Can we use AES for odd number of ...
9
votes
3answers
1k views

Is there an encryption format that preserves length and only outputs alphanumerics?

I'm trying to design a promo code system for a server app I'm designing. Basically, I generate a promo code for a certain item and give the code out to someone, who then types it into the server. ...
0
votes
1answer
47 views

How to deliver an encrypted message to multiple recipients without revealing keys

Let's say I have generated a private and a public key. I create a message and encrypt it with the public key. I deliver this encrypted message and a private key to multiple recipients. Why would I do ...
2
votes
2answers
131 views

Reverse output of general Fibonacci LFSR

Suppose we have some Fibonacci LFSR, and it outputs some sequence. How to change starting LFSR so, that it outputs exactly same sequence, but in reverse order?
3
votes
2answers
193 views

Is simple XOR with secret key using DHE secure?

Client and server have given generator 3 and modulus which is 256 bit prime same all the time for all clients and server (simply hardcoded). They both generate a private exponent and send result to ...
6
votes
2answers
162 views

Is the warning given by chrome warranted?

I went to a payment page on a site recently, and chrome was warning me that the page is possibly not secure, I have a very basic understanding of crypto but not enough to fully understand why this ...
3
votes
1answer
146 views
2
votes
1answer
58 views

Why can we ignore $y$ when using the extended Euclidean algorithm to calculate an RSA decryption exponent?

I have a follow-up question about the extended Euclidean algorithm, as applied to RSA key generation, described in this answer. Let us say we have $p=5$, $q=11$ and $e=17$, so that $N=55$ and ...
1
vote
0answers
636 views

Decrypt using OpenSSL produces packing errors

I am receiving an encrypted file and it's key from a partner. The Key has itself been encrypted using our Digital Certificate Public Key, though I don't know exactly how. The partner has instructed me ...
1
vote
2answers
112 views

Which data encryption mechanism to use for data transfer?

I have high performance nodes communicating with each other sending logs and data over network. The communication is heavy and over public network. I would like to know how to know which is the best ...
2
votes
2answers
480 views

Is it safe to reuse a symmetric key when using asymmetric encryption?

I've written a C# Library that I hope will be used for security purposes in a commercial application. The application will communicate through the internet and not on an internal network. I am using ...
3
votes
0answers
30 views

Authenticate encrypted seed for KEM + AEAD hybrid cryptosystem

Say I want to encrypt something using RSA / KEM and an authenticated cipher. I encrypt using the following scheme: generate random seed z using ...
1
vote
1answer
191 views

Reason for replacing mifare classic

As you know there occured some successful attacks again mifare classic tags (manufactured by NXP) and therefore NXP recommends to replace these tags with some newer products like mifare pro desfire ...
2
votes
2answers
375 views

RSA: Is it secure to use the private key to encrypt and the public key to decrypt?

This may sound weird: What if I don't let others know my public key, then use my private key to encrypt, and the public key to decrypt? Is this secure? Let me explain a little bit: Common usuage: ...
1
vote
1answer
79 views

If my server utilises an RSA based certificate, why does firefox think I am using Diffie Hellman?

I am not a beginner in crypto, but not that far from it, so please be gentle. I look after a web server app that I generated the SSL certificate for, and I used an RSA public/private keypair. When ...
1
vote
1answer
37 views

Variable length variable output encryption with out any padding?

I would like to know if there is any encryption algorithm with variable input variable output with out any padding? For example if I give 16(17,18,67,117,..any size) bit plaintext, my ciphertext is ...
1
vote
0answers
47 views

What is the hardness in Decisional Linear Assumption (DLIN)?

I had understood what does the DLIN assumption means and here is a related question. But I fail to understand the 'real hardness' in this problem. I would be grateful if someone can help me to ...
3
votes
1answer
83 views

Is it possible to encrypt data points but still be able to select the ones “near” a given value?

We have an application where we would like to store "encrypted" data points (as in, not being able to know the original - plaintext - data just by looking at the stored - encrypted - version of it) ...
2
votes
1answer
92 views

Is Shoup's Practical Threshold Signatures considered secure?

I am planning to use threshold cryptography in a Java application. So far, I have only found ThresSig and a ECDSA implementation used in TwoFactorBtcWallet. However, ThresSig is based on a 15-years ...
2
votes
2answers
46 views

(Uniformly) Random Value when an element is picked with $\frac{1}{p-1}- \frac{1}{(p-1)^2}\ $ probability

Let's $\mathbb{F}_p$ be a finite field where $p$ is a large prime number(e.g. 256-bit) I know if the probability that an element picked from the field is $\frac{1}{p-1}$ we say the element is picked ...
3
votes
1answer
131 views

How to enforce data privacy, integrity and authenticity of distributed firmware images for an embedded device?

I'm developing a bootloader for an embedded device, with which it should be possible for customers (i.e. device owners) to update the device's firmware. It is required that: the firmware is ...
2
votes
0answers
38 views

How does FileVault2 Recovery actually work?

I'm a crypto-enthusiast but no expert at all, that'll explain why i didn't understand. Also please consider english isn't my native language :) I am about to enable FileVault2 FDE on the new macbook ...
-1
votes
1answer
49 views

Could someone explain the given algorithm?

The following snapshot of the algorithm is taken from the book Guide to Elliptic Curve Cryptography published by Springer 2004. I don't understand that why at the statement 9.1 if both $T_1$ and ...
4
votes
1answer
135 views

ECDH and ECDSA in PGP with known public key

How are used ECDH and ECDSA in combination with public key ? Usually these methods are used for establish a secret themselves, ...
0
votes
1answer
382 views

How long does it take to brute force a Wordpress password?

I'm not a cryptograhpy expert, I am a web developer trying to determine the origin of a Wordpress blog hack, and how likely it is that it was brute forced. The administrator account username had been ...
-1
votes
1answer
85 views

How To prove Any Change to $v=a\cdot y+b$ maks $y=(a)^{−1}\cdot (v−b)$ Uni. random value [closed]

This question is related to data integrity. Let a finite field be $\mathbb{F}_p$, where $p$ is a prime number. I have a fixed value $y$ and two uniformly random values $a$ and $b$. Hypothesis: ...
1
vote
1answer
86 views

Efficiency of McEliece cryptography (ciphertext expansion)

Most of the sources say McEliece has never gained acceptance because of its large size of private and public keys. However I have never heard about the size (or length) of its ciphertext. ...
4
votes
1answer
107 views

OpenPGP Public-Key algorithm

What means when pgpdump shows this kind of algorithm in the Public-Key Encrypted Session Key Packet? ...
3
votes
1answer
126 views

What is tiger192,4 in PHP?

PHP supports hashing of the following Tiger algorithms: tiger128,3 tiger160,3 tiger192,3 tiger128,4 tiger160,4 tiger192,4 Wikipedia's entry on Tiger says there's Tiger and Tiger2 and provides ...
2
votes
0answers
70 views

How did G.H. Hardy's work contribute to today's public-key cryptography?

I know that Hardy's work in number theory was used by Clifford Cocks in 1973 to develop the basis for public-key cryptography. What specifically was this work, and how is it used today in ...
3
votes
2answers
163 views

Whats the point of an IV if public? [duplicate]

What is the point of the initialization vector in cryptographic modes like AES-CBC when it is sent in the public? Cant any attacker just listen and reverse the IV? and as such defeating its purpose? ...

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