Questions tagged [key-size]

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

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759 views

Why can't we give block ciphers larger keys?

I have limited math's knowledge so sorry if this question sounds stupid. I saw many people complaining about AES, Twofish and Serpent that these ciphers all could be crackable in the near future and ...
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1answer
337 views

Extracting Zip using Only the AES Key

I have set myself a little challenge, to see if I can decrypt my own text file from with a ZIP file... The AES Key from my encrypted ZIP is all I have managed to extract, how do I decrypt the ...
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Why does Laravel only support AES-256-CBC?

Modern Laravel uses OpenSSL to provide AES-256-CBC encryption along with a MAC. However, I was under the impression that this is not a particularly secure approach. Why does Laravel only support AES-...
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1answer
65 views

How secure is a 4 digit seed?

When I Use a 4 digit random number(e.g. 4468) as seed for a (manual) Stream cipher and straddle it to the length of the plaintext using a lagged fibonnacci generator, can this seed be found by brute ...
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1answer
148 views

AES-256-CBC with random IV - storing same plaintext as same ciphertext

I am encrypting some information stored in a column of a MySQL database. The column can contain repeated values, let's say the table has 7 rows and the column to be encrypted has the following values:...
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1answer
438 views

cryptographic accumulators: accumulator size vs. max. number of set members?

Here's a basic question about cryptographic accumulators, or at least ones based on fixed-size accumulator values (such as RSA ones based on modulo arithmetic), that is strangely not even mentioned in ...
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1answer
85 views

Key, plaintext block and ciphertext block permutations question

Question: If a cipher’s key size is $k$ bits and its block size is $b$ bits, how many possible keys are there, how many possible plaintext blocks are there, and how many possible ciphertext blocks are ...
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1answer
238 views

Why is Diffie-Hellman Insecure If Order of the Generator Has Only Small Prime Factors?

In this post from security SE, Tom Leek mentioned that, for Diffie-Hellman to be secure order of the group $g$ should have a prime factor at least $2k$ bits long, where $k$ is the security parameter. ...
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1answer
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How many bits should I request from PBKDF2 to create a strong password?

I'm building a tool which generates passwords by hashing a service name with a master key. PBKDF2 was primarily chosen due to availability in the Web Crypto API. What would be a secure value for the ...
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3answers
228 views

What is the largest key size that could be carried by a shuffled deck of playing cards?

If you are carrying a standard 52 card pack of cards (no jokers) what is the largest key size, or the amount of data the cards can hold? Without the cards being marked or distinguishable from an ...
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1answer
138 views

Is this device authentication method (using AES-256) secure?

Let's say we have: client_id_ran: 256 bit random text (chosen only once for whole system) used to generate client_id by ...
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2answers
800 views

How to encrypt file with RSA and AES that anyone with RSA key can decrypt them?

How to encrypt a file with RSA and AES-256 that anyone with RSA key can decrypt them?.
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1answer
319 views

Differences between Webcrypto (js) and Cryptodome.Cipher.AES (python) [closed]

I'm trying to understand the difference in output of AES decrypt (GCM mode) using Webcrypto and Cryptodome.Cipher.AES in python. ...
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1answer
521 views

Does password length affect AES encrypt/decrypt velocity?

I'm implementing crypto in Node, following this article: https://lollyrock.com/articles/nodejs-encryption/ It defines: ...
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2answers
83 views

Can one trade off the number of iterations for key length with the PBKDF2?

When using the PBKDF2, is one taking on significant risk if one chooses to lower the number of iterations and choose to have very long keys? Can I XOR my message with a a very long key (plain-text ...
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2answers
58 views

Maximum number of possible keys for a fixed-length password?

I'm reviewing some information and possibilities regarding key space size following a unique password requirement, as it were. This particular requirement is a fixed-length password of 12 characters, ...
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1answer
2k views

Encryption / Decryption using AES-256 GCM

I am new in cryptography and I am facing some complications in encryption-decryption. I am trying to use AES-GCM with a 256-bit AES key and a 96-bit nonce. I use an open source project (Vault) to ...
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2answers
523 views

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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1answer
646 views

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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2answers
1k views

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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3answers
2k views

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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1answer
81 views

AES256 mix column code generating output bigger than 8 bits

I'm implementing AES256 in javascript with block size 128 bits and i understand every thing about AES except mixcolumn transformation. so i copied this code from the internet and both mixColumn and ...
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1answer
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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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2answers
102 views

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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1answer
650 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
201 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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2answers
471 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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1answer
235 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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2answers
207 views

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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165 views

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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1answer
2k views

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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2answers
279 views

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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2answers
104 views

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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123 views

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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1answer
109 views

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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1answer
448 views

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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3k views

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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0answers
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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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1answer
2k views

AES with small and large string keys

byte *key; String skey = "abcde" If I convert skey to bytes and uses it to encrypt AES 128 bit, 192 and 256 bits. How AES would work with small key sizes or ...
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1answer
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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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1answer
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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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1answer
646 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 ...