Questions tagged [key-size]

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

201 questions
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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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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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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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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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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 ...
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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 ...
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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 ...
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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.
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What is the maximum size of the plaintext message for RSA OAEP?

OAEP is an important technique used to strengthen RSA. However, using OAEP (or any technique that adds randomness) reduces the size of plaintexts that can be encrypted. Assume for instance that OAEP ...
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Is there any benefit from using SHA-512 over SHA-256 when AES just truncates it anyway?

I am still not very clear on how AES-256-CBC can use SHA-512 bit keys, but I assume that it just truncates the 512bit hash down to 256bit. In software like GnuPG and OpenPGP, is there any real benefit ...
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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?
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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 ...
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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 ...
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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?
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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 ...
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How does the key size in supersingular isogeny schemes relate to their security level?

I'm looking at the De Feo, Jao, and Plût 2014 paper: Towards quantum-resistant cryptosystems from supersingular elliptic curve isogenies. My understanding of section 3.2 Key Exchange, is that Alice'...
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Password entropy much lower than entropy of encryption keys. Why is this acceptable?

When talking symmetric encryption, a 56 bit key is known to be so weak. If you use it for your encryption, you are considered a goner. When talking passwords however, the standard these days is ...
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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 ...
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Master keys' strengh

If I am going to use a master key to generate a session key, why the master key must be "stronger" than the session key? Like should not be distributing 128-bit AES keys derived from a 56-bit DES key....
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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 ...
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Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key itself,...
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Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
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Block cipher block and key sizes

Is there any point in making block size less than key size in block cipher? For example, Russian GOST symmetric cipher uses 256-bit keys to encrypt 64-bit blocks. That means there are many keys which ...
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Key size limitations due to software compatibility?

At the moment, much popular encryption-based software routinely handles up to 4096 bit keys and standard usage is broadly migrating from 1024 to 2048 bit keys. Hashes widely used are MD5/SHA1/SHA256 (...