4
votes
2answers
443 views

Questions about Key Derivation Functions

My understanding is that a KDF is a function that takes a master secret and generates multiple keys. It is secure as long as the keys are "independent". If this is true, the following definition would ...
4
votes
3answers
1k views

NIST temporarily closed — will that have a negative impact on the future of cryptography?

For those who didn't notice yet, in the USA, the National Institute of Standards and Technology(NIST) has been shut down temporarily because of the poor fiscal situation of the USA. The text at their ...
3
votes
3answers
312 views

Where can I find useful data for cryptography/coding theory?

When implementing cryptographic/coding theory algorithms one need to use data like big prime numbers, numbers in $Z_n$ and their inverses, irreducible polynomials in $Z_n[x]$ and so on... While ...
1
vote
3answers
355 views

two public keys with same passphrase insecure? | can two hashes be compared?

Suppose someone had generated a 2.048-Bit RSA GPG/PGP key pair and published the public key on the usual key servers. Then he withdraws this key and generates a new one in 4.096-Bit RSA using the same ...
5
votes
0answers
309 views

Bleichenbacher 1998 “Million message attack” on RSA

I have been reading Bleichenbacher's 1998 paper on a forged message attack on RSA. The paper assumes access to an Oracle that takes a ciphertext $c$ and will check the decrypted text for valid PKCS #1 ...
1
vote
1answer
154 views

Non-linearity of a boolean function

What's the definition of non-linearity of a boolean function? Roughly saying it is minimum number of times it equals any affine function. But I don't get it mathematically. For example, if $f = ...
4
votes
1answer
154 views

Why does only length prepending improve the security of CBC-MAC

I know that length prepending improves security of CBC-MAC. However, wouldn't inserting the length elsewhere (middle, end or any other part of message) be equally good? After all, even the length is ...
1
vote
1answer
256 views

Serpent block cipher : S0 to S7 functions unclear

I am presently implementing the serpent block cipher in C++ following the specifications. It's important to mention that I'm implementing the cipher in bitslice mode. You'll need the The full ...
1
vote
1answer
92 views

Verifying a Signature

Alice publishes $(n,e)$ where $n$ is exponential modulus and $e$ is the public key. We have $n=80$ digit number and $e=3$. Bob, in correspondence with Alice, asked Alice to prove she is really Alice, ...
1
vote
1answer
60 views

Secure MAC implies that probability of same tags on different messages is negligible

So let any secure MAC (message authentication code) be given. Intuitively, I think it is clear that the probability of getting the same tag on two different messages is very small, i.e. negligible. I ...
2
votes
1answer
422 views

OpenSSL padding

I would like to know how much padding OpenSSL algorithms expect.
1
vote
2answers
1k views

Symmetric vs. Asymmetric cryptographic approaches to data security

I know the basic differences between Symmetric vs. Asymmetric cryptography, but I'd love to know more details: Exactly why is the asymmetric approach slower than the symmetric? Why does it make ...
4
votes
3answers
419 views

Order of cascaded ciphers

Does the order of a block cipher cascade (e.g. in TrueCrypt) make a difference to the security provided, assuming independant keys? For example: ...
2
votes
1answer
85 views

How do these figures represent a boolean function?

In the Wikipedia article "Bent functions", there are some figures representing those Bent functions: How do these figures represent a boolean function ?
5
votes
1answer
965 views

What are the advantages of a static ECDH key?

What are the advantages of using "static-ephemeral ECDH" over "ephemeral-ephemeral ECDH"?
6
votes
1answer
359 views

When do ECC patents end?

As the topic says, since when can ECC cryptography be freely used? Isn't it widely used because of patents? There is no alternative to it on embedded devices and smart cards. Just to mention: I am ...
3
votes
2answers
189 views

Encryption of small messages

Some time ago, I asked how to encrypt small messages like e.g., four decimal digit numbers (banking PINs). I've got my answer, but also a warning like it makes no sense as it's easy to guess: Even ...
4
votes
2answers
286 views

Increasing number of rounds in AES

AES-128 requires 10 rounds ( AES Description, Wikipedia ) However Bruce Schneier has recommended AES-128 use 16 rounds ( Schneier on Security: New Attack on AES ) Could that be implemented as two ...
6
votes
1answer
433 views

How exactly was the finalist chosen in the NIST AES competition?

I was just reading the Stick Figure Guide to AES and came across an interesting table explaining how the winner was chosen: Unfortunately the NIST site is down so I can't gain further information ...
0
votes
1answer
149 views

Simple digital signature example with number

I've been looking for a simple which signs a number with some randomly generated key and then verified(decrypts the original number) with the public key, which is generated by the private. All the ...
-1
votes
1answer
617 views

How to hack the new save encryption on ipad for uplink? [closed]

The new iPad version of Uplink appears to be using some newer saving mechanic than the PC/Mac version. Macs and PCs use the REDSHIRT format, but the iPad appears to instead be using ...
0
votes
1answer
105 views

Is there way to combine secrets first and later split them?

Shamir's Secret Sharing allows a secret to be split into multiple shares so that it can be reconstructed later. Is there a way to do the reverse? Can we combine a few secrets first and later split ...
2
votes
1answer
89 views

What is the security risk if an encryption key is not random?

Ok, I just jumped into crypto and now struggling with some points… I read lots of resources, most of them mention how important the strength of the encryption key is. However, I could not find much ...
1
vote
0answers
59 views

Partial encryption of a file?

I want to partially encrypt a large block of data using AES. Meaning: given plaintext[0:1100], I would like to encrypt ...
2
votes
0answers
84 views

What role plays Quantum Fourier Transformation in Shor's integer factorization algorithm?

I cannot seem to understand the role or goal of Quantum Fourier Transformation in Shor's integer factorization algorithm. Is it used to collapse all quantum states into one, in which it has a factor ...
4
votes
5answers
866 views

Any efficient text-based steganographic schemes?

While there are sophisticated and efficient steganographic schemes with images as cover available, I am yet ignorant of the existence of any fairly efficient and secure schemes with texts as cover. ...
2
votes
1answer
146 views

Since it gives negative power, how is rcon(0) calculated in AES?

I'm trying to calculate Rijndael key schedule "Rcon" values manually. I know how to calculate each value with the equation ...
2
votes
1answer
391 views

Two different approaches for Key Expansion using the AES-256 algorithm?

I am implementing AES 256-bit Algorithm from the Theory given in the book, "Cryptography and Network Security" by Behrouz A. Forouzan. The Algorithm described in the Book in relation to ...
4
votes
2answers
1k views

Brute forcing CRC-32

I'm working on a cryptosystem which uses IDEA. The designer made the mistake of including a CRC-32B hash of the password unencrypted in the header, so that the system can quickly reject bad ...
7
votes
3answers
894 views

Understanding CRC

There are zillions of articles describing CRC. What can I read to (more deeply) understand what's really going on? Both from an algebraic perspective and a bit-manipulation perspective, I'd like to ...
19
votes
4answers
555 views

Necessity of Randomness of Salts?

Given the desire to have unique salts for each user of your system, is it actually necessary to create a cryptographically-random salt for each user? If your system already has some other unique user ...
0
votes
1answer
55 views

What makes adaptive memory attack difficult for the adversary?

On page 11, definition 2 of "Simultaneous Hardcore Bits and Cryptography Against Memory Attacks", the paper outlines the following steps (PK,SK) public key and secret key are generated by defender ...
1
vote
0answers
109 views

Cryptanalysis not based on method used to encrypt? [closed]

When doing cryptanalysis on RSA or something number theory based, there are various attacks that all seem to involve number theory (Wikipedia: RSA_(algorithm) ~ Attacks_against_plain_RSA). Similarly, ...
5
votes
1answer
142 views

Initialization Vector Properties

This is a multi-layer problem, and I want to take you through the whole thing rather than just asking about IVs. Bear with me. Also, all code below is in Common Lisp because that's what I'm using, but ...
6
votes
2answers
519 views

Is the encryption of a hash a good MAC?

At university we were told that it is a bad idea to implement a MAC by simply concatenating a key with the data to sign and to run it through a hash function (e.g. $s = ...
0
votes
1answer
137 views

Key space: Dense and sparse

I'm taking a cryptography class and I come across these terms dense and sparse key space allt he time. What do they mean? As far as I can I understand, dense key space means that there are more ...
1
vote
1answer
52 views

RSA Proof - di-mgt - modulo properties

I´m trying to follow one of the very detailed RSA Proofs given by di-mgt: "RSA theory", but unfortunately I stuck at the beginning of solution (chapter 3). I don´t understand where the second part ...
0
votes
1answer
388 views

RSA square and multiply

If an RSA encryption uses a modulus $n$ of 15000 bits and $e = 3$ or $e = 2^{16} + 1$, how many squarings and multiplications will we need for encryption, and for decryption? Could you please explain ...
1
vote
1answer
112 views

Testing if a password for an eCryptfs mount is valid [closed]

I'm using "eCryptfs" on several directories on my dedicated Debian server. I mount them manually via mount -t ecryptfs [dir] [mountpoint] But after some weeks ...
2
votes
1answer
136 views

a possibly stronger type of attack on identity-based encryption

What is known about the security of identity-based encryption schemes against attacks that involve seeing multiple ciphertexts and then receiving the private keys corresponding to some of those ...
1
vote
1answer
137 views

Intuition for random variables in cryptography

I have a simple question about the use of random variables for encryption schemes, to make sure my intuition is correct. We say $P(K = k)$ to represent the probability that a particular key $k$ is ...
0
votes
1answer
103 views

DSA generate signature and verify

I'm trying to generate a signature for DSA with the following parameters: $p = 23$ , $q = 11$ , $g = 3$ , $H(m) = 8$ , $x = 5$ for the life of me, I cannot choose a random $k$ ($0 > k > q$) ...
1
vote
1answer
146 views

How is multiplication inverted in IDEA's decryption round?

As we can see in the picture we have a multiplication in this algorithm, we know that two 16 bit inputs should have a 32 bit output, but here we just use 16 bits of the 32 bit output. For ...
5
votes
2answers
514 views

Examples of applications that use the Schnorr digital signature?

I have made a study on digital signatures, especially on the Schnorr digital signature, and I was just wondering if there is some way I can find names of actual (known) applications that have applied ...
64
votes
3answers
18k views

Should we trust the NIST-recommended ECC parameters?

Recent articles in the media, based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- ...
2
votes
1answer
42 views

How can I evaluate the congruency of an AKS primality test?

Despite the fact primality test is a mathematical issue, it plays a part on the security of many cryptosystems such as RSA. I was trying to understand how it works until I came to the following ...
-5
votes
1answer
1k views

Decrypting encrypted files if i have the original files(Plain Text attack) [closed]

I have the following A Encrypted file and the same file in its original(not encrypted) form Now will it be possible to find the encryption/decryption key by comparing the the above two files are ...
4
votes
2answers
348 views

RSA least significant bit oracle attack

I have been reading up on RSA attacks and came across one that could be called a least-significant-bit (LSB) oracle attack. For the sake of clarity lets define RSA primes $(p, q)$, private key $d$ ...
1
vote
1answer
297 views

Schnorr Identification Scheme under active adversary

According to this paper by Mihir Bellare and Adriana Palacio, Schnorr identification scheme is secure under an active adversary who changes messages. I have been told that Schnorr is actually not ...
1
vote
3answers
156 views

Encoding numbers that can be decoded mentally?

I have a lot of objects, all of which need a particular number tagged on them so I can quickly tell the customer accordingly. But the problem is that the customer should not know what these numbers ...

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