# All Questions

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### Diffie-Hellman secret key choices

I'm trying to understand why the secret keys used by Alice and Bob in Diffie-Hellman are $a,b ∈ ℤ∗p$. Say $a$ is $p - 1$, wouldn't the transmitted $g^a$ be 1 mod $p$ by $FLT$? Now anytime a ...
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### Why does GnuPG save an array of remainders when generating prime numbers?

In looking at GPG's gen_prime() function, found within the cyphers/primegen.c file of ...
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### What is the process to get the n future key for DUKPT? [closed]

I need to get the n future key from my BDK and KSN.
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### Could this possibly be a graphical cipher? [closed]

Back in 2014, KOJIMA PRODUCTIONS published a free video game in secret, using a throwaway studio called 7780s Studios. It's splash screen was a forest with the words P.T. written in the gravestone. ...
28 views

### negligible functions proofs

I'm new in cryptography field and I have few questions. How can I prove that: 1- if f is negligible and g is negligible then f + g is negligible? 2- if p is polynomial and f is negligible then f . p ...
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### How can cryptographic signatures be somehow linked to a physical signature?

A few days ago, I was asked to sign an online document over DocuSign as well as on SignEasy, any the signature were accepted just by a physical signature sent over email or on the app. They did not ...
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### Elliptical curve cryptography Determine if a public key point y is negative or positive, odd or even?

Take a Elliptical curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Example Private key 1 -> (x, ...
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### Sextic twist maps to q Eigenspace of Frobenius

Let $E(p)$ be a Barretto-Naehrig elliptic curve with r-torsion and embedding degree 12 and $E'$ a sextic twist with homomorphism $\psi$. How to show, that $E'$ has a unique r-torsion group $\psi$ ...
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### Powerline password conversion [on hold]

I read this post from Ben Tasker describing how to take control of a powerline network. Since I am interested in security, I tried to do the same thing, to see if it was possible. I used Devolo ...
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### Is there a way to encrypt an integer within an arbitrary range?

I need an algorithm that can take an integer, an arbitrary range, a key of 16/24/32 bytes, and an initialization vector of 16 bytes(ideally), and return an integer in the same range. My latest attempt ...
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### Ciphertext and tag size and IV transmission with AES in GCM mode

I am completely new to using AES in GCM mode of operation, and I have not a very large background in cryptography as well. I have been playing with OpenSSL trying to encrypt and decrypt some messages. ...
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### Is it possbile to get same set of public and private keys twice while creating CSR ? If so where does the conflict happens !?

I'm new to cryptography and please clarify if my below assumption is wrong. Lets assume, that two different banks creating CSR and they get identical public and private key pairs of RSA. In such ...
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### How can a Encrypt-And-MAC scheme be insecure if the encryption is CCA secure?

I was presented with this seemingly paradoxical information, and am hoping someone can explain what I'm missing here. I have an encrypt-and-mac scheme here.If I want to transmit message m to Bob, I'd ...
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### Why is (gy, gx) signed in STS (station-to-station)?

My question relates to the station-to-station protocol as described in https://en.wikipedia.org/wiki/Station-to-Station_protocol [1] and http://cacr.uwaterloo.ca/hac/ [2] p 519. ...
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### PKCS#7 message content

I am using a vendor library that signs a text producing a PKCS#7 message. I'm not sure of the content of this message. Does a pkcs#7 message have to contain the signed message, the certificate, the ...
43 views

### How does the ring settings of enigma change wiring tables?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The site wont allow me too add ...
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### How exactly is an enigma simulation software supposed to encrypt alphabets?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The rotor wiring and other ...
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### Why is the tweak length 64bit in BPS FPE algorithm?

In the algorithm for BPS Format Preserving Encryption Is this tweak always the same length (64bit)? Why did they choose the length 64bit for the tweak?
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### How to install HElib correctly? [migrated]

I followed the installation guide from this repository http://shaih.github.io/HElib/ but when I try 'make Test_General' to run this test I get this error : /tmp/cc3LMsx2.o: In function ...
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### Need some understanding on RSA public key exponent

I am new in cryptography domain and try to build some understanding on RSA key pair generation. My doubt is on RSA public key exponent value . Can exponent be any value (prime or non prime numbers)? ...
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### Encryption algorithm that produces dummy output on incorrect passwords

Background: I've been thinking about using encryption in the context of backing up files to untrusted locations (to the point of making the file publicly and widely distributed for practically ...
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### Paillier cryptosystem, small integers and range of values

First, this a different take on my previous question: Pailler encryption of small integers to 32-bit integers I have to encode small integers (range 0-50) using the Paillier cryptosystem. Those ...
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### OpenSSL CFB Modes [migrated]

I'm trying to understand OpenSSL notation - what is the difference between, for example: AES-256-CFB and ...
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### Proving security of TLS handshake with ProVerif

Background For my dissertation I am working on an application protocol for which I require a TLS session. I am looking to achieve Perfect Forward Secrecy, which means I have selected ephemeral ...
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### How is the server authenticated in ssh? [migrated]

The server does not know any secrets that can be used to authenticate itself. Also, what good is a fingerprint if it is based on the public key if it is basically the hash of some known public key. ...
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### How does the Efficient Fully Homomorphic Encryption from (Standard) LWE work?

I am interesting to learn the low level implementation of Efficient Fully Homomorphic Encryption from (Standard) LWE and I am wondering if anyone can answer the following questions: Does the BV ...
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### Effect of ESSIV when used with XTS

I looked everywhere on the web and I did find a lot of information about full disk encryption, but nothing really answered my question. When formatting a partition to use LUKS, the two most common ...
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### What are the number of output bits of the internal function F used in BPS algorithm?

In the BPS specification document it says We denote by f the number of output bits of the internal function F What is this if the internal function is AES? Would it be the block size (e.g. 128)? ...
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### Timing Attack on RSA

So far I have researched on timing attack on RSA, We all know the ransomware named Cryptolocker it uses RSA 2048 bit encryption. Now is it possible to break the encryption using timing attack. I have ...
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### Do ECDH and ECDSA combined solution provide an authenticated protocol exchange solution in MCU environment?

I'm working on a project in MCU (micro controller) environment with GPRS connection to exchange data securely with the cloud. The encryption algorithm has been selected to use AES. I did some search ...
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### PGP String-to-Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
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### Define “cryptographer”

I often encounter the phrase "I am not a cryptographer". Is there a generally accepted definition for who is a cryptographer? What qualifications would be expected? For instance, should that person ...
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### TLS_PSK and perfect forward secrecy

My question is about how difficult is for someone having compromised the PSK and sniff all (DT)LS handshake, (so getting the NONCE), to get the encryption keys? I understand : getting the pre-master ...
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### Encryption Algorithms in Verilog code

Can we implement Encryption Algorithms like RC4,AES and DES in Verilog? if no what are the limitations?
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### Is this client-side password hash scheme secure?

I want to build an app that uses client-side encryption for storing encrypted data on the server. A user-specific master key would be used, so to easily share it between devices a encrypted version of ...
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### Public SRP verifiers or public hash chain “public keys” when secret is low entropy password

I want to set up the following: An untrusted server should host user sessions and authenticate users without knowing their passwords or being capable of creating a fake user session in the user's ...
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### How do we know a cryptographic primitive won't fail suddenly?

It took more than a decade from when MD5 looked like it was going to break to the point when it was actually broken. That's more than a decade of warning. How can we be sure that when our ...
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### How to pronounce SHA1 and SHA2?

I'm not a native English speaker. So I want to know how to pronounce SHA1 and SHA2 like a native English speaker. Should they be pronounced as [Shar(p) One] and [Shar(p) Two]? Thanks in advance.
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### ElGamal Signatures

I know various applications of RSA signatures. I wonder, is there any real-world applications of ElGamal signatures and encryption?
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### How does the small n attack work?

I'm studying the Lamport's Hash one-time password scheme. This is the scheme: Alice wants to authenticate herself to Bob from a workstation that knows nothing about her. Alice only knows her ...
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### Do we have to consider the cryptographic properties of the decryption, if we're only using the encryption?

Treyfer for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption. Do we have to consider the (bad) cryptographic ...
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### Authentication using AES

I need to implement an authentication mechanism in an embedded environment which does not support floating point operations but has an AES accelerator module which allows for encyption/decryption ...
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### Range-Bounded Commitment fails when implemented? [migrated]

For part of my thesis I must implement (in Java) a Chan, Frankel, Tsiounis range-bounded commitment protocol as quoted in Boudot's paper Efficient Proofs that a Committed Number Lies in an Interval ...
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### Secure “table-look-up” operation

I am thinking about this problem: The server has a two-column table $T=\{c_1,c_2\}$. A user has a query $q$ that is sent to server. The server find an item $x$ in the first column satisfying $x=q$ ...
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### Sign & Encrypt vs. Encrypt & Sign - What does gpg do? [migrated]

I've already read the discussion Should we sign-then-encrypt, or encrypt-then-sign? and the paper Defective Sign & Encrypt in S/MIME, PKCS#7, MOSS, PEM, PGP, and XML. My question has to do with ...
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### Storing sensitive information for a short time, how should I encrypt it or do I even need too? [migrated]

So I will be accepting some sensitive information via a html form, I will be using PHP to store the information. All this has been set up, tested etc. The form works in 4 "steps", each step is its own ...
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### Reuse of a DH / ECDH public key

I was wondering whether it is safe to use the same DH or ECDH key pair in more than one key agreement, particularly if these public keys are in a public registry. These public keys could be used by ...
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### Shared modulus attack on RSA

Consider a scenario in which a group of people use a common modulus $n$ in the textbook RSA crypto system, where $n=pq$, $p$ and $q$ are large distinct prime numbers. Is there any chance for an ...
The HMQV protocol has 2 "identity" fields $\hat{A}, \hat{B}$ that are used in the dual signature - and it tries to guarantee that any properly-generated session key is only shared by a single \$(A, B, ...