# Tagged Questions

AES (Advanced Encryption Standard) is a symmetrical block-cipher algorithm with a 128-bit block size, and key sizes of 128, 192 or 256 bits.

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### What is the DK function when generating an AES key for Kerberos 5?

I'm trying to understand RFC3962. So far I understood everything, except for the last part: generating the derived key from the PBKDF2 output. To generate an encryption key from a pass phrase and ...
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### Are there key collisions in AES-192, AES-256?

Suppose we have a single, fixed plaintext block $p$ of 128 bits. Call the set of all possible 128 bit blocks $B$. We could define fixed plaintext AES-128 as a function $f(k) \to B$ that takes a 128 ...
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### For a given PlainText-CipherText pair how many valid keys are there in AES?

For $PT\in \mathbb{M}$ and $CT\in \mathbb{C}$, let $\mathbb{F}=\{f|f:\mathbb{M}\rightarrow\mathbb{C}\}$ be the collection of all functions from $\mathbb{M}$ to $\mathbb{C}$. Then AES encryption under ...
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### Best practises to generate IV for AES-CTR in this scenario

I'm building a cloud storage application that will store files on my servers. I want these files to be encrypted with AES in CTR mode and the key will be always the same. I'm wondering what would be ...
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### Is there any reason not to use Single-Key EM with AES and a constant key?

I've read recently the paper "Minimalism in Cryptography: The Even-Mansour Scheme Revisited" by Dunkelman, Keller and Shamir where it is claimed that the following construction (Single-Key EM) is ...
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### Public Key Encryption using ECDHE and AES-GCM

Using a text book example, Alice and Bob want to communicate securely using encrypted messages over an insecure channel (the Internet). Alice and Bob have decided to use ECDH (using ephemeral keys ...
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### EC algorithm to derive bits/keys and sign/verify [duplicate]

Looking at the question “ECDSA vs ECIES vs ECDH” it appears that you can either have a tool that can derive keys or bits, or can be used to sign and verify something. Is there an EC way to do both ...
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### Finding key of AES in ECB mode

How many plaintext-ciphertext pairs would be needed to guess with probability, say $p=0.5$, the key $k$ of AES under ECB mode? Most of the articles that I found tried attacks on single ...
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### File encryption using per-user-encrypted shared key

So I'm looking to encrypt files using AES CTR, using a shared key which would be accessed via a per-user password. My two main concerns are: - making sure that the algorithms in use are appropriate ...
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### Simplest way for strong cryptography in chat

I am a beginner in cryptography and I am interested for several weeks on this for my chat application. Basically, it is a centralized model. All messages are stored and potentially visible by ...
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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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### Having doubt in Rijndael Algorithm- coding for decryption

I am doing a project on the Rijndael Algorithm. I have already written the encryption code which produces the correct output. Now I want to implement decryption as well. I'm doing using VHDL, ...
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### equation of mixcolumn in the aes field

$c(y) = (03)y^3 + (01) y^2 + (01) y + (02)$ Let $d = (01)b$ in the AES field $GF(2^8)$. Provide exact equations for the bits $d_i, 0 \leq i \leq 7$, in terms of the bits $b_i$ of b. Can ...
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### Algorithm to transform plaintext to a key of desired keysize, when using input plaintext as key for FPE?

Using a format preserving encryption scheme that uses AES internally as its block cipher, for a plaintext that I encrypt I want to use that input plaintext as the key. However using AES-128, my ...
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### Galois Field ($2^{16}$) for encryption in place of $GF(2^8)$ in AES

AES algorithm is using $GF(2^8)$ Galois Field. What if we use $GF(2^{16})$ in place of $GF(2^8)$? Will this improve the algorithm or not?
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### Designing an AES-based protocol for controlling and acessing ioT boards via RF

I'm designing an open ioT protocol to be used on ioT boards based on Texas Instruments RF-based MCUs. These MCUs have an AES module to easily encrypt and decrypt AES content, so that's why I choose a ...
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### Is there any benefit of changing the AES-CCM encryption key periodically even if the Nonce space is not exhausted yet?

I would like an answer that could be sustained by a mathematical proof. Let's say I'm using AES-CCM to encrypt a lot of messages, and I always use a different nonce. I know that when the nonce space ...
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### AES-256 mode with per-block-key being a SHA-256 of SHA-256 of secret key, random public salt and block number. What's amiss?

Please criticize the (homebrew?) mode described below; to point out a single major defect/uncertainty or the link to (the analysis of) an equivalent construction is quite enough. Assume the ...
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### AES/DES question about determine a key

I have a question. If you receive a DES encrypted message for which you would NOT recognize the plaintext if it were decrypted, is there any way to potentially determine the key if all keys are ...
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### Combining multiple symmetric encryption algorithms - implications?

I was just wondering if I add more security by combining two or more symmetric encryption algorithms on a plain text. For example: ...
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### Why does AES-GCM need a hash/MAC in TLS?

"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256" is just one example for a cipher suite, as far as I'm concerned it means this: It uses the TLS protocol, exchanges keys with Elliptic Curve Diffie Hellman ...
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### Can a file encrypted with one tool be decrypted with different tool? [closed]

I'm new to cryptography and I'm trying implement a file encryption feature into a Python program but I'm running into a big issue...what is needed for someone else to decrypt the file?! Obviously, I ...
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### What is required to decrypt an encrypted file?

At the risk of sounding stupid and being laughed at...I must ask this question. What is required to decrypt an encrypted file? Obviously you need the appropriate key to decrypt, but is any other ...
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### Do I need an IV to use AES-CTR as a CSPRNG?

I'm using AES128-CTR for generating pseudo-random values, which is considered secure for up to 1MB (at least from what I've read). I simply encrypt a 128-bit little-endian counter, starting from 0. ...
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### Is it worth hiding an AES encrypted text string in a PNG image for better security?

I need advice as to whether it is worth the extra "security" and processing of an AES encrypted text string to be hidden in a PNG image as opposed to an AES encrypted text string to be saved in a ...
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### How to derive a key from an existing AES key?

Currently, the code I am staring at uses the CKM_EXTRACT_KEY_FROM_KEY mechanism. That has been disabled in our hardware module, so I need a different mechanism to ...
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### Perfect Secrecy of AES file Encryption

Why does AES file encryption not ensure perfect secrecy? I understand that $\Pr[E(K,M_1)=C_1] = \Pr[E(K,M_2)=C_2]$ given $M1\neq M2$ holds for perfect secrecy of a scheme. However, this seems to hold ...
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### Encrypting a 160-bit plaintext into a 160 bit ciphertext with a 128-bit Block Cipher [closed]

So I have a kind of interesting issue. I have a field in my data store which must take exactly 160 bits of information. Some users will choose to make this data encrypted, some won't, so some of those ...
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### how to get the file used to brute force any encryption method [closed]

Bitlocker as example uses AES 128 Bit encryption as default - if it was brute forced how it can be done , I mean where's the file that will be brute forced to generate the password (If I'm right that ...
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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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### 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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### 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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### 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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### 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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### AES Algorithm processing time in Arduino vs Raspberry Pi

The Arduino employs an 8-bit ATmega series microcontroller whereas the Raspberry Pi is based around a 32-bit ARM processor, and the Arduino is typically clocked at between 8-16MHz and with 2-8kB of ...
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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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### Practical benefit of using a KDF?

I see that KDFs should be used in systems that rely on PSKs, but what practical benefit does it provide? For instance, suppose the system relies on a shared secret for AES encryption and decryption. ...
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### Switching between AES and a highly performant algorithm

I want to de/encrypt several binary files rather frequently on a normally battery-powered device. My goal is to use AES-256 when the device is AC-powered and a highly performant algorithm when it's ...
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### (Re-)Using deterministic IV in CTR mode / How to: deterministic AES

I am aware of the requirement of an IV to be unique in CTR mode (Why must IV/key-pairs not be reused in CTR mode?). However I wonder if I can use an IV depending on the plaintext deterministically. ...
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### Attacks on WinRAR volumes reusing same password?

I have quite a few WinRAR volumes that are all encrypted with the same password. The password is long and unbruteforceable, but I recently read that WinRAR uses PBDKF2 as its key-derivation function ...