# 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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### How to generate backup key for PBKD functions?

I would like to encrypt some files using AES, Ill derive key from password using some standard PBKD function and use that as AES encryption key. My question is, if user forgets the main password, ...
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### Why is GCM only usable for ciphers with a 128-bit block size?

All block cipher modes of operation that I understand are generic schemes. They are not restricted by key size or block size. So why is GCM restricted to 128-bit block size?
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### How to use AES correctly in BPS Format Preserving Encryption

I have several questions on using AES 128bit in the BPS format preserving encryption Which modes are acceptable? (Should the block cipher used at each round be deterministic (ECB) or probabilistic (...
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### Which ECB ciphertext stealing scheme is this?

I am stuck with identifying ciphertext stealing method with the following properties: mode of operation is ECB; recommended padding scheme for this application is PKCS#7, but apparently it is not ...
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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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### 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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### 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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### Is it safe to use single-block AES for mutual authentication?

I read the question Symmetric mutual authentication with client using a derived secret and its answer which, if I'm not mistaken, assert that it should be safe to use the proposed protocol for mutual ...
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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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### 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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### generate RSA public key having public modulus and exponent [closed]

i want to generate an RSA public public key file using openssl (or other tools) having public modulus and exponent, so i can use it later to encrypt files i have this: ...
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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 ...
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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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### Is reverse NTRU still secure?

I'm currently prototyping something with the NTRU encryption scheme but I wish to use it in "reverse" -- distribute private keys so anyone can decrypt, but keep the public keys secret and thus only ...
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### If I compute the SHA-1 of all possible 40 digits hexadecimal strings, will I get all possible sha1 hashes? [duplicate]

Wikipedia says sha1 produces a 160-bit (20-byte) hash value. So if I compute the SHA-1 of all possible SHA-1 values, which as far as I understand is at current time impossible both to calculate and ...
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### research on Encryption for master [closed]

I'm tring to choose an way for an Encryption mothod for my research? So,I want to choose one-layer encryption or multilayer encryption,and I want it to be easy to applicable. when I search about it, ...
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### Is this scheme to derive multiple keys secure?

I need a cryptographic scheme to generate a deterministic chain of private keys that look random to outside observer but can always be reconstructed from a single root key, also: Neither private ...
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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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### Digital signatures using a partially public key

I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices. To ...
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### Blowfish and DES small block size and maximum message size

Would the following affect the maximum message size limititaion of Blowfish and DES due their small 64 bit block size? Let's take Blowfish for example. You take a 256 bit Blowfish key, quickly ...
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### Is there a standard format for compact 56-bit DES keys?

DES keys are traditionally stored as 8-byte blobs, with only the high 7 bits of each byte being meaningful to the algorithm; the low bit of each byte is set so that the population count of the byte is ...
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### Help defining a shift cipher mathematically

For an assignment question, I am trying to prove formally that double encryption with two keys by the shift-cipher encryption function results in a shift cipher as well. If the Shift-cipher encryption ...
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### What is the significance of the Period of a Steam Cipher [duplicate]

If we only know the period of a Stream Cipher, let's say 150-200 bit in length, how can we use this information to attack a stream cipher? Taking a look at this link, What is the period of a cipher? ...
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### Are there any existing ASN.1 structures for transferring symmetric keys?

Is there any reasonable ASN.1 standard to encode symmetric keys? I found PSKC, but it seems extremely heavy, and I can't quite find any library (e.g. bouncycastle) that would simplify using it. If ...
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### Secure method for encrypting 32 byte private keys

I am using 32 byte EC private keys on the client side of a web application. These keys should be securely stored on a server database. The keys should be encrypted (AES) before being sent to the ...
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### Number generation for Fujisaki-Okamoto commitment scheme parameters

I need to implement the Fujisaki-Okamoto commitment scheme for a project such that I can demonstrate performance of various zero-knowledge proofs in relation to one another, for example Boudot's "...