Questions tagged [key-size]

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

Filter by
Sorted by
Tagged with
4
votes
3answers
935 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 ...
2
votes
1answer
400 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 ...
14
votes
3answers
5k views

AES Key Length vs Block Length

This answer points out that certain key and block lengths were a requirement for the AES submissions: The candidate algorithm shall be capable of supporting key-block combinations with sizes of 128-...
1
vote
1answer
703 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'...
3
votes
2answers
331 views

How can encryption software accept password lengths which are not one of the AES key lengths?

AES comes with key sizes of 128, 192, and 256 bit. But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit. How is this ...
5
votes
5answers
862 views

Effective security of block cipher – equal the key size, or half the key size?

The Wikipedia “Key Size” article states: The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most symmetric-...
-2
votes
1answer
618 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 ...
0
votes
2answers
130 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? ...
0
votes
1answer
628 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 ...
3
votes
1answer
861 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?
3
votes
2answers
855 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, ...
5
votes
3answers
11k views

RC4 Keylength Limits

While reading the Wiki page on RC4 I noticed that the key size must be in the range of 40–2,048 bits. Why is that? Is there a reason it can't have a lower or higher length?
4
votes
1answer
4k views

ECC vs RSA: how to compare key sizes?

I know and I have understood the details of RSA, elliptic curve cryptography, (EC)DH and (EC)DSA. I keep reading everywhere that (if we don't consider non-deterministic computers) "ECC can achieve ...
0
votes
1answer
1k views

Probability of guessing random 128-bit AES key

Consider the following five events: Correctly guessing a random 128-bit AES key on the first try Winning a lottery with 1 million contestants Winning a lottery with 1 million contestants 5 times in a ...
2
votes
1answer
80 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 ...
2
votes
1answer
547 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 ...
1
vote
0answers
175 views

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 ...
1
vote
1answer
231 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 ...
7
votes
2answers
5k views

Is it possible to change PGP / GPG Key Size on an exisiting key?

Is it possible for myself to change the key size (say from 2048 to 4096) on an EXISTING PGP / GPG key, and just republishing that key? Or do I have to generate a new key all together? I want to say ...
6
votes
2answers
17k 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 ...
0
votes
1answer
100 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.
11
votes
5answers
2k views

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 ...
0
votes
1answer
345 views

How does the time complexity of block cipher change with increase in key length?

I am interested especially in the case when the keylength exceeds the length of the plaintext. Intuitively, it should be harder to crack the key with an increase in key length even if it exceeds the ...
9
votes
2answers
10k views

How many keys does the Playfair Cipher have?

I was just studying the Playfair cipher and from what I've understood, it is just a slightly better version of a Caesar cipher, in that it isn't actually mono-alphabetic but rather the 'digrams' are ...
0
votes
1answer
843 views

Hashing entropy to generate 256bit key?

I have a 256bit fully random entropy source from dices, which is probably not cryptographically secure. I have read that it's customary to take the hash of the entropy source in order to generate a ...
1
vote
1answer
158 views

Explain: An NTRU key for a lattice of dimension $d$ has size only $O(d\log{d})$

The associated NTRU lattice is of dimension $d=2N$. The public and private key sizes are both of length $O(N)=O(d/2)=O(d)$. So where does the $d\log(d)$ appear? Thanks in advance.
6
votes
2answers
4k views

Is RSA key size the size of private key exponent?

I have implemented a key pair generation scheme for RSA algorithm. I have taken the length of private key exponent as RSA key size, but then I've got to know that RSA key size is the size of the ...
4
votes
2answers
417 views

For RSA keys, is the safety of a given key-length different for signing vs encryption?

I'm wondering if considerations of key-length are different when thinking about signing vs encryption. If for some reason, it was safter to use smaller keys for signing that would be interesting.
-5
votes
1answer
131 views

AES cryptography keys

What are the three possible values (in bits) for the length of the AES algorithm keys? Approximately how big is the AES key space?
2
votes
2answers
113 views

Discrete logarithm key sizes for very short term usage

We have this special use case that our session typically only last for less than 30 minutes, no more than 1 hour at most, after the session finished, the information protected does not matter. Each ...
1
vote
1answer
2k views

How to determine the RSA Private key size from the Public.key file?

Question: How to determine the RSA Private key size from the Public.key file? Just roughly, how big it could be? ...
1
vote
1answer
177 views

What are the typical input lengths for KDFs?

I am looking for typical input lengths for key derivation functions like the HKDF. I know the parameters of HKDF, but can not find any information about typical input sizes to HKDF or any of the other ...
0
votes
1answer
3k views

How to calculate key size for Diffie-Hellman key exchange?

How to calculate key size for Diffie-Hellman key exchange? The strength obviously depends on both generator and prime modulus. Formula: $$g^x\bmod p$$ Public values: $$g=3$$ $$p=...
1
vote
2answers
2k views

Why would an RSA library tell me that the public key must be at least 512 bits in size?

I'm trying to interoperate with a web service by reverse-engineering it. Currently, when sending a POST request, it encrypts the form data one-by-one with a 'RSA' function. But it's rather weird as ...
6
votes
2answers
7k views

How long should a HMAC cryptographic key be?

In the top answer to this question the answerer says 'with a sufficently long key'. I am using a SHA1-HMAC (may switch to SHA256-HMAC) algorithm to verify cookies sent to clients as authentication ...
3
votes
1answer
249 views

Special case of 3DES

3DES uses EDE as it is backward compatible to single DES, but consider the following case $K_1$=$K_2$=$K_3$ which one is more secure EDE or EEE.
1
vote
1answer
160 views

Does passphrase length impact read-write speed?

I'm using Diskcryptor to encrypt a 2TB external USB HD and the process is taking over 2 days. I chose a 100-character strong encryption key passphrase (because, why not?) and am now wondering if the ...
2
votes
1answer
309 views

Is it safe to use the same key for different variants of the HMAC-SHA algorithm?

I need to apply HMAC-SHA hashes in my application. Depending on the context I'll use either HMAC-SHA512, HMAC-SHA256 or HMAC-SHA1. Is it safe to use the same key for all of these algorithms, or do I ...
1
vote
1answer
400 views

M-94 disk cipher keyspace

If the M-94 had only 10 disks, what would be the keyspace of the resulting cipher and what is the useful keypspace of the 10 disk cipher?
3
votes
1answer
2k views

Why is RSA-2048 max input 245 bytes?

I can see that the message (after padding) should not be 256 bytes because it might be bigger than the modulus of RSA. So I think that the message should be 255 bytes, but I saw posts that says the ...
3
votes
4answers
1k views

Staying PCI compliant while upgrading encryption

I am trying to migrate my encryption methods, currently I use RSA 1024 key size and hashing with SHA-1. This configuration is going to be deprecated soon, but 2048 key size will have my system so ...
14
votes
2answers
8k views

Argon2 output length and parameter storage?

I just started using the libsodium port for .net today and the output length parameter kind of confused me (I'm using the argon2i implementation). With my limited exposure to hashing, whatever hash ...
1
vote
2answers
115 views

Clarification on Size of an Encryption Key

Given a key with a certain key size (e.g., 64bits). Would I be correct to interpret this as 8 characters (since each character would be 8 bits under ASCII encoding)? Because the ASCII scheme is ...
4
votes
1answer
810 views

what are the NTRU keysize and application in industry?

I'm a student currently working on a research project on the NTRU cryptosystem, I've read some papers about this cryptosystem, and in those papers they are talking about keysize, is it the size of the ...
2
votes
1answer
530 views

Requirement for the length of a HMAC tag?

I've seen NIST requirements about key length. What about the output lengths ? Is 112 bits enough for the HMAC output length ? Can we truncate the tag to keep only 112 bits ?
4
votes
2answers
5k views

How to measure ECC key size?

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
4
votes
0answers
77 views

Computing cost for a trillionaire to compute GNFS in RFC 3766

RFC 3766, Section 4.1 discusses picking $n$ to achieve some target cost for employing the GNFS, i.e., $T$ is known and $N$ is unknown in the below equation: $$T = \kappa \cdot \exp{\left(c \cdot (\ln{...
2
votes
1answer
48 views

Older key as PGP subkey?

Currently I have a 2048-bit PGP key. Suppose I create a new 4096-bit key. Can I add that old key as a subkey of this new one?
11
votes
3answers
9k views

How secure is AES-256, but with an effective key length of 56-bits?

I need to encrypt a few drives using Kaspersky Total Security. I however noted something peculiar, Kaspersky's description of their cipher is: Data will be protected using AES-256 encryption with ...
1
vote
1answer
259 views

How can I determine key length for message encrypted by many-time-pad?

For message $ m $ and key $ k $ I get encrypted message $ c $ ($ m \oplus k = c $) where $ length(k) < length(m) $. Additionally I know that message $ m $ is English text. Instead of using pure ...