Cryptography

Questions tagged [key-size]

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

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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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262 views

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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269 views

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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131 views

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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60 views

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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520 views

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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223 views

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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RSA encryption secure mode, plaintext length limit vs. key length

I have two questions about RSA encryption to confirm: Assume use RSA 2048-bit key pair, what is the secure encryption mode? Are ECB / OAEPWithSHA-256AndMGF1Padding and ECB / OAEPWithSHA-...
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90 views

Disk storage of RSA and DSA keys

I have generated one RSA-2048 signing key and one DSA-2048 signing key, using gpg command gpg --full-generate-keys I would expect the key to have size 2048 bits, ...
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Why the output of elliptic curve based cryptosystems is smaller than the ordinary public key cryptosystems?

I am trying to understand how much the output of elliptic curve based cryptosystems (for example elliptic curve ElGamal) is smaller than the ordinary public key cryptosystems. I know that the ...
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Use large key size for RC4 to avoid RC4 bias

I saw a question on StackOverflow where RC4 was initialized by a 1024 bit key (with 2048 the maximum key size, if I'm not mistaken). Will such a large key size possibly solve any of the bias of the ...
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Prove that for key with $n$ dimensions, the order of the key is $k!$

I need to prove, that for a key with $n$ dimensions, they order of the key would be $n!$ and to prove that, I need to use mathematical induction: $$\text{Let n = 1} \Rightarrow {1} \text{ if there ...
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Why are AES keys increments of 64-bits?

Why are AES keys increments of 64-bits? Rijndael, which subsequently became AES, allowed key increments in 32-bits (128, 160, 192, 224, and 256 bits). However, AES made it 128, 192, or 256. My guess ...
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Key size of a repeating key XOR-encrypted message using Hamming distance

To find possible key sizes for an encrypted message, I break the message into blocks with length s, ...
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611 views

Requirements for RSA key parameters

Recently I'm working with a chinese vendor for POS devices and their devices use 2048bit RSA keys for signing binaries. I had to generate a public/private pair (so I can sign my own binaries) and I ...
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Are all sizes of RSA keys possible? [duplicate]

I mistakenly thought that RSA keys could only be powers of two(1024, 2048, 4096 etc.) but a few days ago read about a 1536-bit and 1160-bit RSA key. I am wondering is it possible to have an RSA key of ...
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Are short ElGamal keysizes acceptable (1024-bit or lower) in cases where security is only necessary in a short timeframe

I am working on an efficient mental poker framework. I have implemented a functional and secure commutative encryption scheme based on ElGamal as described in: http://groups.csail.mit.edu/cis/theses/...
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Effect of longer key on DES security

I am reading a book on cryptography and the author states that one of the complaints of the research community was that DES key length was chosen to be too short. I am trying to depict how DES would ...
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Recommended key size for DKIM

What is the recommended key length for DKIM? I'm currently thinking about a 1024-bit key vs. a 2048-bit one. From the crypto point of view for RSA, 2048 or 4096 bits is clearly recommended--no ...
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Security of ciphersuite and key

Is anyone able to cite resources that can be based on choosing a cipher suite? In my case, for a VPN server (OpenVPN) I chose a set of ciphers: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 It provides 128 ...
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Why is the NIST recommendation for the private key exponent so much smaller than the modulus?

NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. This question answered how the modulus was chosen/calculated, however, why isn't the private key size closer to the ...
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When does the SIS (Short Integer Solution) Lattice-problem start becoming easy (According to the parameters size)?

SIS (Short Integer Solution) Problem : Given $m$ uniformly random vectors $a \in Z_q^n$, grouped as the columns of a matrix $A \in Z_q^{n.m}$, find a nonzero integer vector $z \in Z^m$ with $||z|| \...
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How is the recommended NIST modulus for DLP chosen/calculated?

NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. From this answer it appears that the range of private key numbers is derived by calculating a prime modulus via $2⋅p$ ...

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