Key size is the size measured in bits of the key used in a cryptographic algorithm.
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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
43 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
35 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, ...
2
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2answers
53 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
118 views
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
31 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
1k 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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44 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
201 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
55 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
107 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
85 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
636 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
253 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
91 views
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
56 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
303 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
264 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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0answers
107 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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50 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
204 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
701 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
86 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
121 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
47 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
232 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
413 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
60 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
591 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
268 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
322 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
419 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
423 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
195 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
404 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
117 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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0answers
160 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
339 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
293 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
700 views
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
618 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 ...
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0answers
66 views
How to handle operation containing large private key?
I am implementing Oblivious transfer protocol, for which I have to do the following operation?
n = k0 ** d % n
where d is a private key
I am using ...
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1answer
293 views
Paillier's Cryptosystem - Secure Key Size
Given Paillier's Cryptosystem. What size in bits would be considered secure for now and the near future? I know it differs for every cryptosystem.
For reference, the most important part of my ...
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Can you travel out of the U.S. with Oracle's JCE Unlimited Strength installed on your laptop? [closed]
Just curious if this "export" restriction applies to general travel outside the U.S. with Oracle's JCE Unlimited Strength installed on a laptop.
pertinent text from Oracle's "Java SE BCL License ...
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1answer
159 views
Bruteforcing a 64-bit key
Diffuse the 64 bit key into eight 8 bit blocks. Each block can be brute forced in 2^8 steps. Thus, eight 2^8 steps and in total 2^11 steps are required for brute forcing. Is this kind of brute force ...
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2answers
10k views
What is the maximum key size for a 128 bit AES?
What is the maximum key size for AES 128,
Will using a key greater than maximum gives extra security or error? Is there a minimum key size?
Suppose a key is 128 bit, does it means The key is of ...
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1answer
90 views
Which public key cryptosystem has the highest security/keysize rate?
I'm working on a 16-bit processor msp430 and I need to know what I need to study when it comes to key size efficiency of a public key cryptosystem.
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What is the purely mathematical definition of encryption strength?
An encryption function can be used to obfuscate pieces of information and later on retrieve them.
What is the yardstick for measuring how well the function encrypts the information ? Given any ...
