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

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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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0answers
30 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
91 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
46 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
78 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
75 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
165 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
90 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
46 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
256 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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76 views

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
145 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
81 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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0answers
47 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
155 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
570 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
82 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
120 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
46 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
195 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
327 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
59 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
547 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
248 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
194 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
297 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
379 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
176 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
351 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
115 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
147 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? ...
0
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1answer
301 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
254 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
677 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
544 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
77 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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54 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 ...
2
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1answer
259 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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0answers
105 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 ...
2
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1answer
146 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
9k 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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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 ...
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1answer
612 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
164 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
134 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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1answer
3k 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 ...
13
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1answer
5k views

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 ...