Questions tagged [key-size]
Key size is the size measured in bits of the key used in a cryptographic algorithm.
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Why is the NIST recommendation for the private key exponent so much smaller than the modulus?
NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. This question answered how the modulus was chosen/calculated, however, why isn't the private key size closer to the ...
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1answer
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When does the SIS (Short Integer Solution) Lattice-problem start becoming easy (According to the parameters size)?
SIS (Short Integer Solution) Problem : Given $m$ uniformly random vectors $a \in Z_q^n$, grouped as the columns of a matrix $A \in Z_q^{n.m}$, find a nonzero integer vector $z \in Z^m$ with $||z|| \...
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How many possible keys are in a columnar transposition cipher?
In a book I am reading it says that the message "Common sense is not so common." (which has 30 characters, space and punctuation included) has a range of possible keys of 2 to 15, half the message ...
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1answer
76 views
How is the recommended NIST modulus for DLP chosen/calculated?
NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. From this answer it appears that the range of private key numbers is derived by calculating a prime modulus via $2⋅p$ ...
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44 views
Can I use XOR to establish a longer shared secret?
SIKEp434 can only be used to encapsulate a 16 byte (128 bit) shared secret key. Most encryption algorithms these days (specifically (X)ChaCha20) require a 256 bit key to be secure, especially in a ...
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43 views
Maximum security strength in bits of ISAAC cipher?
Wikipedia claims key length can be very big in this cipher, so I assume it can offer a million bits of security provided entropy of key is the same?
Of course I can SHA-256 hash the key to allow any ...
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Minimal secure index of quasi-cyclic codes for code-based cryptography
It is well-known that keys (generator matrices) of code-based cryptography are very large for its practical usage. To reduce them scientists propose to use families of quasi-cyclic codes. I remind ...
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Security strength of JPBC Type A curve compared to SecP curve
I recently encountered some problems when learning about the JPBC library.
Does the curve generated by (J)PBC using the method typeAcurvegenerator(160,512) and the ...
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1answer
102 views
Guessing the key in AES256-GCM? [duplicate]
I assume that my case is weird but I've the following information:
IV: 0x263e or 0x3e26
Auth tag: 0x25
AES256-GCM encrypted payload: 0x4eec96df534ade4c013a
AES256-GCM decrypted payload: ...
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4answers
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80-bit collision resistence because of 80-bit x87 registers?
This is just a curious question, and it probably doesn't belong here anyway, and I'm just being bold asking it here.
80-bit used to be considered an adequate level of security, Skipjack and SHA1 ...
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1answer
60 views
How secure is a 4 digit seed?
When I Use a 4 digit random number(e.g. 4468) as seed for a (manual) Stream cipher and straddle it to the length of the plaintext using a lagged fibonnacci generator, can this seed be found by brute ...
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1answer
291 views
cryptographic accumulators: accumulator size vs. max. number of set members?
Here's a basic question about cryptographic accumulators, or at least ones based on fixed-size accumulator values (such as RSA ones based on modulo arithmetic), that is strangely not even mentioned in ...
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1answer
66 views
Key, plaintext block and ciphertext block permutations question
Question: If a cipher’s key size is $k$ bits and its block size is $b$ bits, how many possible keys are there, how many possible plaintext blocks are there, and how many possible ciphertext blocks are ...
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1answer
165 views
Why is Diffie-Hellman Insecure If Order of the Generator Has Only Small Prime Factors?
In this post from security SE, Tom Leek mentioned that, for Diffie-Hellman to be secure order of the group $g$ should have a prime factor at least $2k$ bits long, where $k$ is the security parameter.
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How many bits should I request from PBKDF2 to create a strong password?
I'm building a tool which generates passwords by hashing a service name with a master key. PBKDF2 was primarily chosen due to availability in the Web Crypto API.
What would be a secure value for the ...
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1answer
639 views
What is the recommended minimum key length for ECDSA signature
I want to identify the proportion of certificates that use unrecommend ECDSA key length for TLS certificates based on some data I collected.
By looking at a standard like NIST for example, I find ...
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3answers
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What is the largest key size that could be carried by a shuffled deck of playing cards?
If you are carrying a standard 52 card pack of cards (no jokers) what is the largest key size, or the amount of data the cards can hold?
Without the cards being marked or distinguishable from an ...
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2answers
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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
50 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
311 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
467 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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1answer
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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
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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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1answer
494 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
135 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
302 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
132 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
647 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
1k 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
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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
79 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
495 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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0answers
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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
946 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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1answer
341 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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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
396 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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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
95 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
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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
50 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 ...
0
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1answer
364 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
956 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
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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
862 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
364 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
589 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
565 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
658 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
235 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 ...
