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Questions tagged [key-size]

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

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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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1answer
349 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
172 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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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
91 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 ...
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1answer
701 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 ...
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1answer
247 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 ...
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1answer
140 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.
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4k views

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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1answer
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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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119 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?
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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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1answer
162 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 ...
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1answer
2k 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=...
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1answer
229 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.
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Find the length of the key knowing the size of the key space and the size of the alphabet

I have a key consisting of some alphabet characters {A, B, C, ...}. I know that my machine can test $10^9$ keys per second and I know how long it takes to test the ...
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4answers
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Finding length of a key for a given vigenere cipher using Index of Coincidence

I'm developing an algorithm that takes in a vigenere cipher and produces the key length automatically. However, I'm having trouble understanding how to detect the key length when there are multiple ...
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139 views

Can you compress an elliptic curve private key in half?

According to this, a $n$-bit key offers about $n/2$ bits of security. That got me wondering, can you compress the key in half? At first blush, no, because the key is essentially a random number, and ...
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1answer
151 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 ...
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1answer
350 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?
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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 ...
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4answers
772 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 ...
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1answer
238 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 ...
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2answers
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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 ...
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2answers
98 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 ...
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Getting a key size of DSA/Elgamal certificate

I've tried to get a public key size of DSA/Elgamal PGP certificate. Using the Cleopatra I find out that there is actually two public keys - one with DSA with key ...
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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{...
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1answer
45 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?
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1answer
195 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 ...
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2answers
168 views

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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2answers
1k views

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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1answer
102 views

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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2answers
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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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1answer
124 views

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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1answer
112 views

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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2answers
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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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0answers
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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 (...
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1answer
3k views

How many bits of symmetric security does RSA-3072 actually provide? [duplicate]

I know that the sizes are standardized to $1024$, $2048$ etc. but they actually provide different security than $128$, $256$... for example $\texttt{RSA-}2048$ is actually $112$ bits of security and $...
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2answers
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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.
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1answer
476 views

PyCrypto and AES: can i use a longer key than the block size (16byte)?

I see that in many scripts are used keys of 16 characters for a block of 16 byte, but can I use key of 40 (for example)? And then why in some scripts with aes module the block size is set to 32 byte ...
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2answers
130 views

Does a key derivation function always generate an even distribution of bits in the resulting key?

I am a student of crypto. During our study course, we went into the AES-128 algorithm. All the examples given used an initial key k, 128 bits and we only briefly touched on the key derivation of ...
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113 views

Does encrypting with MGF1/SHA-512/1024-bit seed equal to a 1024-bit key block cipher?

Suppose: Alice uses SHA-512 with MGF1(as in PKCS#1 V2) and a 1024-bit random seed to generate a mask, XORs the mask with a message(M), gets a cipher text (CT), and sends the CT to her old friend Bob....
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1answer
1k views

Do 2DES and 3DES2 have the same effective key length?

I am following the notes "Introduction to Modern Cryptography" by Bellare and Rogaway, and on the chapter about blockciphers there is the following claim (page 11 of https://cseweb.ucsd.edu/~mihir/...
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1answer
350 views

How to calculate secret key size of a CP-ABE scheme

How can I calculate the real size of key in a CP-ABE scheme. For example, I have this GSWV scheme: Fuchun Guo, Willy Susilo, Duncan Wong, Vijay Varadharajan: CP-ABE with constant-size keys for ...
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2answers
742 views

Why are recomended RSA key lengths so high? [duplicate]

I was checking for authoritative sources to back up my recommendation of a minimum RSA key length of 1024 and was shocked to find that NIST 800-56Br1 and FIPS 186-4 both recommend at least 2048 bits ...
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1answer
2k views

Is a 4DES or 5DES system possible?

We know that 3DES is created with $E_{K_3}(D_{K_2}(E_{K_1}(m)))$ to extend DES's key length. Is it possible to extend it further by repeating this pattern? Perhaps using $E_{K_5}(D_{K_4}(E_{K_3}(D_{...
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2answers
363 views

Diffie-Hellman key size to symmetric formula?

I've noticed that on every site I checked I kept finding the relationship between D-H key size and symmetric encryption equivalent as a table, like: 384 - 56 768 - 80 1792 - 112 2304 - 128 10753 -...