Questions tagged [key-size]

Key size is the size measured in bits of the key used in a cryptographic algorithm.

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Why would Diffie-Hellman Group 21 be 521 bits rather than 512?

Diffie-Hellman groups tend to increment in key sizes as you'd expect up until group 21. Any idea why the key size is 521 rather than 512? I haven't been able to find an answer at all.
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X25519 - why openssl shows 253 bits?

When using ECDHE with Curve25519 with openssl: Server Temp Key: X25519, 253 bits I thought when we use X25519, it use 256 bit key. Why openssl shows the server temp key as 253 bits?
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What is the minimum and maximum value of an RSA private exponent?

Is it possible to calculate the minimum and maximum value of the private exponent for an RSA key, for example for a 1024 key size? In other words, what is the range of values in which the private ...
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Mathematical formula for switching the key for OTP?

Instead of generating the random key for the one time pad cipher over and over again, is there a mathematical formula that allows you to switch the key to a new key? The new key must be as random and ...
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1 Billion Bit Encryption?

So, browsing through YouTube, I stumbled on this video interview of John Draper (Captain Crunch), one of the first "hackers". He talks for about 3 minutes (until 27:48) about his home rolled ...
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Which symmetric algorithm should I use for storing files in untrusted servers?

I have gigabites of files, which I have to backup. I have some servers for storing this files. But these servers are untrusted. So I need to encrypt files, then backup files. When my PC breaks down, ...
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AES Is it safe to expose the plaintext and cyphertext in the same place,

In a web application, I need to send in a webpage form an id (my plain text) and then retrieve it back when the user submit the form. But i need the id to be protected, so malicous users can't send an ...
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943 views

Does C# Triple DES Encryption need 128 bit key or 192 bit key [closed]

I have the following code in C# ...
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1answer
316 views

Cutting down the size of a long blowfish key

I am reverse engineering a software that uses blowfish for encryption. The target uses an implementation of blowfish that allows arbitrary positive key length with a key size larger than 56 bytes. I ...
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869 views

Arbitrary key size in RC4

Is it possible using RC4 that for e.g. a 17-bit long plaintext i can get a 17-bit long ciphertext? From my understanding, for this example i need a 17-bit long key to do the XOR operation for ...
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416 views

what method of transposition does AES 256 encryption use

I'm interested in learning how to use AES-256 encryption in C/C++. I'm still a beginner in Cryptography but I'm confident in my abilities to program. There is still a lot for me to learn about this ...
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How does the key size in supersingular isogeny schemes relate to their security level?

I'm looking at the De Feo, Jao, and Plût 2014 paper: Towards quantum-resistant cryptosystems from supersingular elliptic curve isogenies. My understanding of section 3.2 Key Exchange, is that Alice'...
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Why aren't 4096-bit RSA PGP key blocks $\lceil\frac{4096}{6}\rceil=683$ base64 characters long?

If a 4096-bit RSA PGP key is considered sufficiently long for most purposes, why are so many key blocks around 3000 base64 characters in length? Why aren't $\lceil\frac{4096}{6}\rceil=683$ base64 ...
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Will using a 32 character key for Blowfish make it a 32 bit encryption?

I am sorry if it sounds naive but I have been searching and searching regarding what kind of encryption we end up with if we use a key of length 32 characters? This article https://www.embedded.com/...
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Should text be hashed before being used as an encryption key?

Let's say I have an API that provides an encryption wrapper around another API. I give the consuming programmer the option of either passing a string or byte array as an encryption key. The byte ...
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How to calculate the key size of my cryptographic system

I have a 'for fun' project, which is a pure software based redesign of the Enigma I. I'd like to compute the key length of my design, but I need some help with that. I have a write-up here (see ...
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Why is keysize almost always expressed in bits?

I've never actually seen a time when somebody has expressed RSA keysize in bytes, and I haven't seen keysize expressed in bytes in other encryption algorithms either (can't be certain that that's ...
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Safely using ciphers that take small key sizes

Is it feasible to use triple encryption for block ciphers with the maximum keysize being the only significant security issue? I mean $C = E_{k_1}(E_{k_2}(E_{k_3}(P)))$ and $P = D_{k_1}(D_{k_2}(D_{k_3}(...
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Blockcipher: key space define permutations of blocks

An $n$-bit block cipher is a keyed function $f_k:\{0,1\}^n\rightarrow\{0,1\}^n$. There are $2^n!$ such functions. Most block ciphers seem to have only $2^n$ keys, although there is an AES mode that ...
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Key size and finite fields in ECC (References)

So somehow I know that the key size in ECC is defined over the number of elements in a finite field or that it is almost equivalent to that (Correct me if I am wrong). However, other than on Wikipedia ...
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Why exactly Blowfish max key length is 448

Could anyone, please, tell me history of birth of Blowfish algorithm? Specifically, what is substantiation of Blowfish key length to be in range from 32 till 448 bits? Why, for example, it wasn't 64-...
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Is 512-bit RSA still safe for signature generation?

The standard CSP on Windows XP only supports RSA up to 512-bit, which means that it's the maximum key size I can use for authenticity verification of updates. The public key is embedded in the updater,...
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Are 80-bit keys considered secure as of late-2017? [duplicate]

I've seen a lot of ciphers with variants that use 80-bit keys, like Grain, Trivium, KLEIN, KATAN & KTANTAN, Piccolo, PRESENT, RC4, Skipjack, and TWINE. Some of these designs are younger than six ...
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What are the practical differences between 256-bit, 192-bit, and 128-bit AES encryption?

AES has several different variants: AES-128 AES-192 AES-256 But why would someone prefer use one over another?
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Finding length of a key for a given vigenere cipher using Index of Coincidence

I'm developing an algorithm that takes in a vigenere cipher and produces the key length automatically. However, I'm having trouble understanding how to detect the key length when there are multiple ...
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112 views

Why should the factors $p,q$ of $n$ be half the bit length of $n$ in RSA?

Why do we want the factors $p,q$ of $n$ to be of size half the bit length of $n$ in RSA? I know $p,q$ need to be large so that it is harder to factor $n$ and if one of $p,q$ is small, then it is more ...
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Determining key size in bits by knowing plaintext and ciphertext

I need to know how can I determine the key size in bits knowing the ciphertext and the encryption algorithm used? For example suppose the plaintext was "ABC" and after the encryption it became "DEF" ...
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Existence of 99% successful unbounded adversary against randomized secret key encryption scheme with short keys

It can be shown that if $E$ is a deterministic encryption with key of length $n$ and messages of length $l\geq n + 10$ then there exist two messages $m_0$, $m_1$ and a strategy for Eve so that given ...
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Does limiting the sales market to U.S. only, releive my application of Export Admin Regs? [closed]

I have a steganography application that uses one-time-pad encryption. Obviously, key lengths can be very long. If I were to limit the sales market on the Microsoft Store to U.S. only, would that be ...
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859 views

how to calculate the average key search for AES-128bit?

Assume that an attacker has a special purpose application specific integrated circuit (ASIC) which checks $5\times 10^{8}$ keys per second, and she has a budget of $\$1$ million. One ASIC costs $\$...
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Is there any benefit from using SHA-512 over SHA-256 when AES just truncates it anyway?

I am still not very clear on how AES-256-CBC can use SHA-512 bit keys, but I assume that it just truncates the 512bit hash down to 256bit. In software like GnuPG and OpenPGP, is there any real benefit ...
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584 views

Keyspace in truncated MD5 hash?

I have identified a password hashing algorithm that uses a truncated MD5 hash to compare user passwords. This means that any password whose hash matches the same first 23 hex chars (11.5 bytes or 92 ...
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1answer
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Does FHE's longer key bring more security than traditional encryption algorithm?

I check some key size which FHE libraries generated, for example, HElib's key size will be more than 300M, while tfhe's is also ...
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1answer
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Key and signature sizes of NTRU and NTRU Prime?

I would have expected this info to be easier to Google Scholar for, but alas I'm asking here. Partial answers: NTRU key size (confused) the public key consists of one ring, and so it takes up $11 ...
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AES Key Length vs Block Length

This answer points out that certain key and block lengths were a requirement for the AES submissions: The candidate algorithm shall be capable of supporting key-block combinations with sizes of 128-...
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972 views

Understanding Key space

I've looked at a few previous posts on this site but I'm still struggling with the concept of keyspace. Specifically I'm following a coursera course but I think it's probably too advanced for me as I'...
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How can encryption software accept password lengths which are not one of the AES key lengths?

AES comes with key sizes of 128, 192, and 256 bit. But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit. How is this ...
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Effective security of block cipher – equal the key size, or half the key size?

The Wikipedia “Key Size” article states: The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most symmetric-...
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How important is length and complexity of personal password for AES-256 encryption?

I want ask you how important is to have complicated personal password for AES-256 crypto? For example if I use these two "types" of passwords: pass123 ...
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Is there a way of increasing the time to brute force a cipher, but by increasing the ciphertext size instead of the key size?

If you have a symmetric-key algorithm that is limited to using a small key size (say 40-bits) is there any way you could increase the resistance to brute force attacks without increasing the key size? ...
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1answer
962 views

What are some of the best prime factorization algorithms and their effecitvity

I was wondering aren't the most used prime factorization algorithms a symbolic mile behind the security of the RSA cryptosystem? The way it looks to me is that every time an algorithm is able to ...
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For RSA, is there a specified size range for $p$ and $q$ when calculating $N$?

Is there a specified size range for $p$ and $q$ when calculating $N$? For example, what size would $p$ and $q$ be when $N$ is 1024 bits?
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Brute-forcing Symmetric Keys

Random keys are often produced using high-quality random generators. Assuming a key produced for a symmetrical cipher, this means that the number of zeros and ones in the key will, on average, ...
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RC4 Keylength Limits

While reading the Wiki page on RC4 I noticed that the key size must be in the range of 40–2,048 bits. Why is that? Is there a reason it can't have a lower or higher length?
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ECC vs RSA: how to compare key sizes?

I know and I have understood the details of RSA, elliptic curve cryptography, (EC)DH and (EC)DSA. I keep reading everywhere that (if we don't consider non-deterministic computers) "ECC can achieve ...
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Probability of guessing random 128-bit AES key

Consider the following five events: Correctly guessing a random 128-bit AES key on the first try Winning a lottery with 1 million contestants Winning a lottery with 1 million contestants 5 times in a ...
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How important is the size of the public key (for a given security level)?

I've read about different signature schemes which for the same bits of security differ largely in the size of the public key: The ones proven in the standard oracle model perform worse than the ones ...
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Paillier's Cryptosystem - Secure Key Size

Given Paillier's Cryptosystem. What size in bits would be considered secure for now and the near future? I know it differs for every cryptosystem. For reference, the most important part of my ...
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Can you travel out of the U.S. with Oracle's JCE Unlimited Strength installed on your laptop? [closed]

Just curious if this "export" restriction applies to general travel outside the U.S. with Oracle's JCE Unlimited Strength installed on a laptop. pertinent text from Oracle's "Java SE BCL License ...
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Bruteforcing a 64-bit key

Diffuse the 64 bit key into eight 8 bit blocks. Each block can be brute forced in 2^8 steps. Thus, eight 2^8 steps and in total 2^11 steps are required for brute forcing. Is this kind of brute force ...