Questions tagged [key-size]

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

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What are Key Size requirements (rather than modulus size) for different Asymmetric Algorithms for 112-bit security?

A lot of writeups, books & webpages say that to get 112 bit security (i.e $2^{112}$ steps), you need to use RSA or DH with 2048 key size or ECDH with 224 key size. In reality, I think what is ...
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Is it possible to generate a key from a hash function, being the key larger than the hash function digest output without spliting the seed?

Let's suppose I have a 2MB photo and I want to generate a key from it, and the key should have 2048-bits of size. A hash function such as SHA3-512 would not deliver a key with with the desired ...
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Security of the encryptions, using a PRG for the keyGen

I recently got doubtful to the usefulness of psuedorandom generators(PRG) in cryptography. Based on Kereckhoff's principle, we always assume that the used algorithms are made public. So, when we use a ...
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Are there any encryption schemes where more than one key give the same encryption and decryption operations? [duplicate]

Given an encryption scheme that takes as input a key $k$ and converts it to an encryption operation $E$ via the function $M(k) = E$, is it possible that more than one $k$ can give the same $E$? For ...
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IIS Crypto 3.2 not getting rid of Diffie Hellman algorithms of less than 2048 bits ... or am I missing something?

I'm trying to stop a server using Diffie Hellman algorithms of less than 2048 bits ..but I'm getting confusing results I've run ...
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Historical key sizes for RSA and discrete log [closed]

What is the historical pattern for key size increases for rsa vs discrete log? What are the current and future projected sizes for these?
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64 bit key size Diffie Hellman

I am building a cryptographic El Gamal implementation on the Cardano Blockchain for a poker game. Each hand the players generate a DH 64 bit keys and shuffle the cards together via homomorphic ...
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Can the security margin of any Feistel block cipher be multiplied if I just multipy the number of rounds and use different random subkeys each round?

Kaweichel is a port of Blowfish for 64-bit architectures, its key size accepted is 1920-bytes, instead of 16 rounds it has 32 rounds, the double of Blowfish. ICE is a feistel block cipher that has a ...
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Does the security margin of Kalyna block cipher double per for additional 4 rounds? Would be possible to create a version of it with larger key sizes?

I believe this question should be directed to the authors of Kalyna block cipher, but I think they cannot answer me because of the war they are facing in their country actually. I know that AES uses ...
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Confusion of message space and key space

i just a bit confused that is it reasonable to assume that the probability of sending message $m \in M$ is uniformly distributed over the message space $M$? How is this different from assuming that ...
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Small public key size or small signature size, which is preferred?

Suppose two signature schemes provides the same level of security. The sum of the sizes of a public key and a signature, i.e., sizeof(sig) + sizeof(pk), are equal in the two schemes. One of the ...
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Argon2 allows a huge key length in input, but does it really provide the security of the key provided?

I read the Argon2 specification. It says in 3.1 (Page #5): Secret value K (serves as key if necessary, but we do not assume any key use by default) may have any length from $0$ to $2^{32}\text{-}1$ ...
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Is multiple encryption with XTS mode susceptible to Meet-in-the-middle attacks?

Let's suppose I encrypt something with AES-256 in XTS mode two times (there will be 4 four keys, 2 for each encryption operation), wanting to achive 512-bits of security. Will this scheme be ...
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Is there a way of preventing meet-in-the-middle attack when using double-encryption?

Let's suppose I encrypt something with AES-256 two times using 2 different keys wanting to achieve 512-bits of security. I know that this scheme will in fact give me only 257-bits of encryption ...
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How much information is required to specify a new variant of AES beyond the key length and the number of rounds?

Three different versions of the Advanced Encryption Standard (AES) have been standardized, which use keys of bit length 128, 192, and 256 respectively. They also use different numbers of rounds: 10, ...
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Can the security of Salsa20/Chacha20 be expanded to 448-bits if I fill the nonce and the Nothing-up-my-sleeve numbers with key material?

As I studied, Salsa20/Chacha20 is basically a hash function that accepts a 64-byte input and returns a output of the same size of input. 128-bits of the input are filled with four "Nothing-up-my-...
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How can a generate a key with defined key size with a hash function with its security/internal state shorter than the key?

Let's suppose I took a high resolution photo full of entropy and I want to convert in a key with 2048-bits of security. Practically all the known hash algorithms have maximum 512-bits of security. Is ...
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Nexor, an encryption algorithm that promises unlimited key sizes: Is it safe?

My intention is not to make spam here, but I came across this project in Github: https://github.com/andrewhodel/nexor It's an algorithm called Nexor, it promises encryption with unlimited key sizes. ...
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Hashing 64-bit counters with different keys and XORing to blocks of plaintext, multiple times: Some questions

Let's suppose I want a 2048-bit block encryption. I take a 512-bit hash funcion (as Blake2b), provide a counter and a key and hash the counter and so XOR the hashed value in a ciphertext block, and ...
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Questions about Blake2x: Its state size (internal state) and its security when generating keys with size more than 256/512bits

I read the Blake2x paper: https://www.blake2.net/blake2x.pdf It says Blake2x can be used to build a "DRBG" (CSPRNG): https://csrc.nist.gov/glossary/term/deterministic_random_bit_generator &...
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CTR and OFB block cipher modes and their post-quantum security. Some questions [duplicate]

It's said that quantum computers can break block ciphers with 2^(n/2) queries (being n the key size). I read this paper: https://eprint.iacr.org/2016/197 It says that CTR and OFB modes are safe ...
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What's bad about idea of public-key/one-time-pad hybrid cryptosystem?

As i know, generally nowadays hybrid protocols are more widely used than either symmetric or public key cryptosystems separately. I read that public key system is used to exchange and share secret via ...
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Questions: Argon2, its internal state and security of it when generating keys larger than 256/512 bits

Let's suppose I want to use a cipher with a large key size, such as ISAAC that supports 8192 bits ogf key. I can hash with sha-256 or sha-512 and iterate until reaches the key size but I won't get ...
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Bringing a key to 256 bit by a hash algorithm

For example, if I use Rijndael for encryption, I have to specify a key of a certain length. For user convenience, I want the user to be able to use a key of any length. Then, to get the key to the ...
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Breaking vigenere cypher using the one-time pad flaw when used for a second time

I got an idea which may be wrong because I may have missed some important factor but for the moment I don't know if I really did. Let BM be the method used to break a reused one-time pad cipher (which ...
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how to break AES [duplicate]

why is breaking a (asymmetric) 1024 bit RSA key less difficult than breaking a 128 bit (symmetric) AES key? Breaking RSA key involves finding the prime factors of a large number. What is involved in ...
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Why can't we have AES512 or more? [duplicate]

Look I know AES256 is ridiculously secure but to keep aes secure even after quantum computers, I have a concern. Using the Grovers theorem aes can be reduced from 256 to 128 bits for brute force ...
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How does AES-256 works if AES is only a 128-bit block cipher?

I'm currently studying AES encryption and I'm quite confused on how do we use a 256-bit key in AES? Becuase in my understanding, AES no matter what the key size is, it still operates and encrypt a 128-...
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Constants of 128-bit key version of the stream cipher Chacha [duplicate]

I am trying to find constants of 128-bit key version of the stream cipher Chacha. I know for 256-bit key version, constants are 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574. Are these same for both ...
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Can we determine the size of n-bytes before encryption by AES-128?

I am writing a program in python to encrypt files. This program takes subsequent 1024*1024 (1 mebibyte) chunks of data from a file and encrypts it using AES-128. This is performed in a loop until all ...
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How many Bits/Bytes is a public key, given its encoding

I am struggling to understand what the "bit/byte" size of a public key is, how you can work it out, and even what it means. An example of a RSA public key is: AAAAB3NzaC1yc2EAAAABJQAAAQB/...
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Time Complexity of Exhaustive Search Algorithm

I have the sets $S_1=\{2,10,20,6\}$ and $S_2=\{25,26,20\}$ and I want to find which numbers sum to make 32. This is very easy by inspection; 6 and 26. It seems similar to the Knapsack problem, but I ...
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Key space of a substitution cipher

I was going through a cryptography course, and I found a question there that: What is the size of the key space of the substitution cipher with 26 letters? Its answer was 26! I am not sure what this ...
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When using prime factorization for key gen, is there a limit on the size of the prime factors?

If there is a limit, does that leave a limited number of prime numbers that can be used for key gen? And, if that is the case is the encryption system vulnerable?
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Public key size for different elliptic curves

Let's say I want a certain level of security (eg 128 bits) when using ECIES but I also want to minimise communication, does the elliptic curve used matter on the size of the public key? If it does ...
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So is AES-256 more secure or less secure than AES-128 after all?

It seems there are attacks that work more effectively on AES-256 than AES-128, which makes it less secure in some cases. But the bigger key size should add some safety margin on the other hand, for ...
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Does key sizes specified in ASD Approved Cryptographic Algorithms impact operational performance?

Does the key sizes specified in Australia's ASD Approved Cryptographic Algorithms impact operational performance? The larger the key size the slower the operational performance. Is it true? The set of ...
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Is it alright to generate RSA keys with bit sizes other than 512/1024/2048?

I am keep generating RSA keys for 512/1024/2048/4096... as bit size. Each time the key length is increasing. Is it possible to generate/use keys other than the ...
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Is there much difference in a RSA-4096 over RSA-3072 for support/speed and security?

I am in the process of created a signing certificate and i have an option of RSA-4096 or RSA-3072. Is there much difference in security between the two? I know people say RSA-3072 should be good until ...
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Is it possible to increase the encryption security of a short key?

If I encrypt a file with a short 4 digit pin is there any way to make it more secure. I've thought about hashing the 4 digit pin and using the result as the encryption key. I think this would work as ...
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Leighton-Micali Hash-Based Signature key sizes

I am working with the RFC for Leighton-Micali Hash-Based Signatures: RFC-8554. The question is if I understood it correctly and my calculations of the key sizes are correct. Basically, LMS uses ...
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Small values with non-uniform distribution encoded as large values with uniform distribution

Given a non-uniformly distributed set of 32-bit values (for example), is there a way to reversibly encode each one as a 128-bit value (for example) where they'd be approximately uniformly distributed ...
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Can you use a dynamic key and data size for KMAC?

I've asked before if some kind of canonical encoding should be used on the input parameters of SHA-3 before it could be used as replacement for HMAC. However, if I read the current NIST specifications ...
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What are the public key and output sizes for the four remaining PQC KEM candidates?

Currently there are only 4 direct candidates left that provide KEM. Generally performance seems to be "OK" for those candidates. However, the key and encapsulated key sizes (i.e. the output ...
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What grade of protection does a private key's passphrase provide at best?

Does a passphrase with high entropy provide the same level of security as the private key itself? General scenario: An attacker has access to a private key file that is protected with a passphrase ...
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Bruteforcing a symmetric cipher [duplicate]

I don't understand how we could bruteforce a symmetric cipher. Let's take AES with a key size of $128$ as an example. It means that there are $2^{128}$ possible keys, and as many ways to decrypt a ...
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Calculating symmetric key bit strength

16 byte key where each byte is in range 0-255, generated using cryptograhic PRNG will be believed to have 128 bit strength. What would be a bit strength of a key generated using same quality PRNG, ...
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Cryptography standards on key size

There are many limits on key size. As far as I know 56 bit in USA and 40 bits in India without license. On the other hand much higher 128 bit or 1024 or 4096 bit for banking and other purposes. So ...
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Chaining signatures of different parties

My question might be quite beginner, so please pardon my ignorance :) So, assume there are 10 parties, each with their own keypairs. There is a message $M$ that is passed from one party to the next. ...
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How to calculate time needed for decryption of 64-bit key

I am having trouble figuring out how long it takes to decrypt a 64-bit key, given that a computer can do 1 billion trials per second. I know that there are $2^{64} = 1.844 \times 10^{19}$ possible ...

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