Questions tagged [key-size]

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

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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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How can I change the McEliece main parameters?

I use the Bouncy Castle Crypto API to implement McEliece in Java. I have also managed to encrypt and decrypt a message and it works without any problems. When I use the debugger, I see that the ...
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If a Pseudorandom Function (PRF) is supplied with a key with the same size of output block, can 2 or more keys generate the same output for a input?

There a 2 examples: A block cipher with 128 bits of block size taking a plaintext and a 128 bits key (AES-128). A keyed hash function with 1024 bits of block size in its output, taking a message and a ...
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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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Implementation of a decryption mixnet, and problems with the size of the key

I've been studying decryption mixnets, in the context of e-voting and stealth networks. Let's describe it in a very simplified way. The concept is pretty simple. A message M is forwarded through ...
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"16-bit DES encryption algorithm"

I need to use encryption software from PSpice for my SPICE model. In a user guide on page 71 they claim to use a "16-bit DES encryption algorithm". According to the wiki DES is using a 64-...
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Is there any cryptographic scheme with block size more than 128 bit

I am asking this question out of curiosity if there are any cryptographic algorithm that has a block length more that 128 bit. I am new to cryptography and I didn't know any. AES 128, 192, 256 all ...
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Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
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Symmetric algorithm effective key length

If we have a symmetric algorithm with key length $m$ bit, and we do a 5 time encryption with it. How much will it be its effective key length.
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Do ciphers with a key size of 64 bits still have use under very limited attack models?

If we have a very performance critical interactive session, like a video game, running on a trusted platform (video game console). If our goal is to prevent exfiltration of up to date information (...
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The order of reading bits in blocks

Let's say I have a cryptographic algorithm that encrypts on 128-bit blocks and makes 20 rounds. Each round has its own keys (one of 72 keys per round). We read blocks before each round. But we're ...
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How to calculate RSA Key Size correctly starting from 384 bits to 15360 bits or beyond 15360 bits

Hello fellow experts here, I am new to cryptography. Recently I looked into RSA Key Size (Microsoft RSA library), it actually describes that the minimal key length required is 384 bits and maximum ...
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How to properly cypher 16 bytes message containing a CRC checksum?

This question arose from a new context under early developments. If cryptographic operations are not well chosen or badly sequenced, please do notice it along your answer or comments: I am a layman in ...
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What is the current security level of an algorithm?

I was reading a paper of some years ago about a cryptography and a phrase got my attention. We want to ensure a security level of at least $2^{80}$ I know that $2^{80}$ was used as rule of thumb ...

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