Questions tagged [key-size]

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

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Using longer key with PKCS#5 derive_key() function for AES256? [closed]

I have code where someone made the key 64 bytes (32*2) and passes to the derive_key() function. It then uses the key created for ...
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Would this 3AES-192 scheme achieve 384-bit key security with just a 384-bit key?

For starters, I don't need any don't-roll-your-crypto stuff. We're discussing a hypothetical. So the idea is 3DES needs 3x the key size and achieves only 2x key size bit security. So using the 3x ...
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Does ECC give the most secure assymetric cipher for a given public key size?

Cracking an ideal block cipher is basically a brute force key enumeration. The complexity of the attack is exponential, growing as $2^b$. Cracking ECC is also exponential, but the cost grows as $2^{\...
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Entropy output from 256-bit Argon2 input [duplicate]

I would like to deterministically derive two different 256-bit keys from a single passphrase -- one used as an ECDSA private key, the other as a symmetric key for AES-GCM. Would a KDF output ...
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What is the security of XTS block cipher mode of operation if the key is much larger than the block size?

I made two Linux kernel modules of Hasty Pudding Cipher with key size of 16896-bits (16384-bits key + 512-bits tweak also called "spice), one has 512-bits of block size, the other 128-bits. I ...
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How much can we compress RSA public keys with two equal size factors?

Can we define an RSA variant in which the public key with $n$-bit public modulus $N$ has a compact representation of $\kappa\ll n/2$ bits, with a security argument that it is as safe as regular RSA ...
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Effective key length in Enigma encryption

Each Enigma machine setting induces a certain encryption in the sense of a function from the space of plain texts to the set of cipher texts. The number of different Enigma machine settings can be ...
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A question about "attacks on MAC key space"

At page 336 in "Handbook of Applied Cryptography - Menezes", I see the sentence For $n$-bit MAC with $t$-bit key space this requires $2^t$ MAC operations, after which one expects $1+2^{(t-n)...
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Encryption scheme with variable and provable key-length

I'm currently studying the possibility of a novel ransomware technique, where an adversary instead of forcing the victim to pay a ransom, forces them to brute force a key of given length and thus ...
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Securing symmetric ciphers with 56-bit keys

Under the Wassenaar Arrangement and applicable export control law, symmetric cryptography of an (effective) key size of 56 bits or less is (generally) exempted from export control. I am forced to work ...
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Homomorphic Encryption - Integer modulus in HEAAN and key sampling

I am trying to wrap my head around Homomorphic encryption, specifically the HEAAN/CKKS scheme. I am reading through the publication, but I am getting stuck on page 11, namely the KeyGen and Enc ...
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Threshold Paillier encryption key generation time

I have used the threshold version of Paillier encryption without a trusted dealer in an application. I have tested the key generation phase with different security key sizes such as 80, 512, 1024, and ...
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Does this RSA decryption scheme make sense?

A custom file format has a header encrypted with a 2048-bit RSA public key. I need to decrypt it using a 2048-bit RSA private key. The header has 48 bytes, and according to the scheme I got for the ...
Maksym Shcherban's user avatar
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Understanding RLWE Encryption

LWE Encryption Scheme by Regev is inefficient due to its public key sizes in $O(n^2)$. This led to the variant problem RLWE, defined in this paper : Let $n$ be a power of two, and q a prime ...
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What bitlength should I use for generating primes for a ElGamal Encryption Cyclic Group (given the data to encrypt has a short time-value vector)?

I am generating large prime numbers to create a cyclic group for ElGamal encryption, I can specify the bit-length n but want to limit the size because this will ultimately allow me to limit the amount ...
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What kind of symmetric key ciphers are secure thanks to the intrinsic cryptographic method instead of making the key length very long and secure?

For example, Threefish has a key length of 1024 and a very long number of rounds (80). but, I have not heard much about Threefish-1024 being particularly secure, so what symmetric key ciphers are ...
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Cracking an XOR crypt with a know key length [closed]

I'm trying to crack a crypt with a known key length. I deduced that the operation made was a hex XOR. Here is the crypt: ...
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They key size of the Schnorr Signature Algorithm

Based on the Schnorr signature below: What is the suitable size of lamda to generate a secure key?
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Could Blowfish be extended to larger block/key sizes if increasing the level of sum and XOR operations?

Blowfish encryption is made as follows: ...
phantomcraft's user avatar
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Is BLAKE2X suitable for generating keys with any security in bits event if BLAKE2 having only 256/512-bits?

I can generate a key of any security in bits with any hash function from random source with enough entropy by using the following scheme: $$H(00||S) || H(01||S) || H(02||S) || H(03||S) || \cdots$$ /\ ...
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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 ...
phantomcraft's user avatar
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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 ...
Quantum Guy 123's user avatar
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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 ...
phantomcraft's user avatar
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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 ...
phantomcraft's user avatar
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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 ...
FoolishB's user avatar
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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 $2^{32}\text{-}1$ ...
phantomcraft's user avatar
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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 ...
phantomcraft's user avatar
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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-...
phantomcraft's user avatar
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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 ...
phantomcraft's user avatar
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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. ...
phantomcraft's user avatar
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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 ...
phantomcraft's user avatar
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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 &...
phantomcraft's user avatar
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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 ...
phantomcraft's user avatar
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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 ...
nimrodel's user avatar
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1 answer
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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 ...
phantomcraft's user avatar
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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 ...
Luqus's user avatar
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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 ...
george s's user avatar
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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 ...
Ashwin's user avatar
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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-...
0xdeadbeef's user avatar
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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/...
MeBadMaths's user avatar
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2 answers
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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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