Questions tagged [key-size]
Key size is the size measured in bits of the key used in a cryptographic algorithm.
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Creating new cryptographic algorithm instead of using known algorithm
Does it invent a new cryptographic algorithm in case of military encrypted communications makes the communication safer?
Keeping the structure and behavior of the protocol unknown is an advantage?
2
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1answer
113 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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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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109 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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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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1answer
82 views
What is the recommended minimum key length for ECDSA signature
I want to identify the proportion of certificates that use unrecommend ECDSA key length for TLS certificates based on some data I collected.
By looking at a standard like NIST for example, I find ...
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3answers
179 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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55 views
Key-space analysis of an algorithm
I have an algorithm that requires a set of keys to encrypt a text (image of size N x N). It is an image encryption algorithm for a project. The key can be thought of as a tuple
$x_0, \lambda, d, i, ...
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2answers
52 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
40 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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2answers
106 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
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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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0answers
52 views
Is it possible to successfully encrypt/decrypt in DUKPT using different sized BDKs?
We are having our P2PE Solution validated against the PCI P2PE standard. We currently use a TDEA 2-key based BDK, and IPEK in both the encryption and decryption environments. ANSI X9.24-1 (2009) ...
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2answers
2k views
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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58 views
find keylength in xor-based encryption
I have found interesting answer, written by GeneQ and now want to understand and implement it. I think, that first point of this answer can be rewritten in follwing way:
suppose we have n bytes of ...
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1answer
293 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
67 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
143 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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2answers
103 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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2answers
641 views
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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1answer
608 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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2answers
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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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1answer
62 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
364 views
384-bit ChaCha20 / Salsa20
The standard Salsa20 core is a $\{0,1\}^{384} \to \{0,1\}^{512}$ PRF with a 16 byte constant ($\sigma$ for a 32-byte key), an 8 byte nonce, an 8 byte counter, and a 32 byte key. The hash function does ...
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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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2answers
395 views
How do I calculate a password space if the password only has eight alphabetic characters (not case sensitive)
I read this wiki article and saw this formula for random password's information entropy. Also the wiki article mention that the symbol count for non case sensitive is 36. Is there a way I can ...
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165 views
Post-quantum candidates for asymmetric cryptography with small key sizes
One of the things that I have come to like about elliptic curve cryptography is that the key only needs to be twice as long as the desired security level. That's a very small expansion (I also like it ...
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60 views
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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1answer
281 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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1answer
909 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
88 views
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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2answers
133 views
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
49 views
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
262 views
Keyspace in truncated MD5 hash?
I have identified a password hashing algorithm that uses a truncated MD5 hash to compare user passwords.
This means that any password whose hash matches the same first 23 hex chars (11.5 bytes or 92 ...
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2answers
524 views
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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1answer
64 views
Does FHE's longer key bring more security than traditional encryption algorithm?
I check some key size which FHE libraries generated, for example, HElib's key size will be more than 300M, while tfhe's is also ...
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3answers
688 views
How confident can we be that nobody will crack a 128-bit key?
In a context involving a block cipher like AES-128, excluding quantum computers, cryptanalytic breakthrough on AES and implementation attacks (poor TRNG, DPA..), and wrench, how confident can we be ...
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1answer
303 views
Key and signature sizes of NTRU and NTRU Prime?
I would have expected this info to be easier to Google Scholar for, but alas I'm asking here.
Partial answers:
NTRU key size (confused)
the public key consists of one ring, and so it takes up $11 ...
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1answer
398 views
Understanding Key space
I've looked at a few previous posts on this site but I'm still struggling with the concept of keyspace. Specifically I'm following a coursera course but I think it's probably too advanced for me as I'...
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1answer
451 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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4answers
505 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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2answers
207 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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1answer
466 views
How important is length and complexity of personal password for AES-256 encryption?
I want ask you how important is to have complicated personal password for AES-256 crypto?
For example if I use these two "types" of passwords:
pass123
...
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2answers
123 views
Is there a way of increasing the time to brute force a cipher, but by increasing the ciphertext size instead of the key size?
If you have a symmetric-key algorithm that is limited to using a small key size (say 40-bits) is there any way you could increase the resistance to brute force attacks without increasing the key size? ...
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186 views
Key size vs output size of a MAC
What is more important, in terms of security, the size of the MAC or the size of the key that it uses? I'm asking this because I have to answer the following homework question:
What is more secure? ...
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1answer
402 views
What are some of the best prime factorization algorithms and their effecitvity
I was wondering aren't the most used prime factorization algorithms a symbolic mile behind the security of the RSA cryptosystem?
The way it looks to me is that every time an algorithm is able to ...
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1answer
419 views
For RSA, is there a specified size range for $p$ and $q$ when calculating $N$?
Is there a specified size range for $p$ and $q$ when calculating $N$? For example, what size would $p$ and $q$ be when $N$ is 1024 bits?
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2answers
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Brute-forcing Symmetric Keys
Random keys are often produced using high-quality random generators. Assuming a key produced for a symmetrical cipher, this means that the number of zeros and ones in the key will, on average, ...
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1answer
789 views
Are 256-bit SSL certificates still secure?
I was looking at the SSL certificates of various major web sites and I notice that Google is using a 256-bit SSL certificate:
...
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1answer
78 views
How important is the size of the public key (for a given security level)?
I've read about different signature schemes which for the same bits of security differ largely in the size of the public key: The ones proven in the standard oracle model perform worse than the ones ...
