3
votes
2answers
152 views

Finding Private key in RSA with public key, cipher text and plain text

Is there a known 'non-brute force' method of determining a private key in an RSA system when all other parameters are know? I found the values of a ciphertext ($C$), its corresponding plaintext ($P$) ...
3
votes
0answers
27 views

Breaking linear blockcipher - expanding recursive formula

I am trying to break a block cipher that can be defined as follows: We have 12 rounds and at each round we perform the following operation. We split 64 bit data into 2 parts each 32-bits, $\ x_r$ ...
3
votes
1answer
43 views

Selective and existential unforgability of signature schemes

I understand that one can define EUF-CMA of a signature scheme is terms of a game where the adversary is allowed to query signatures on messages of his choosing, and at the end of the game he must ...
5
votes
1answer
136 views

What are the minimum constraints on RSA parameters and why?

The RSA cryptosystem only works if certain constraints are applied to its input parameters. Some of those constraints are made to make it "hard" to determine the private key whereas other constraints ...
3
votes
0answers
28 views

Publishing only items your subscriber previously subscribed to, without you knowing which those items are

Let's say you were given a dump from a security breach. You want to share the email addresses affected by the breach with a separate company who pays you for this service so that they can protect ...
10
votes
4answers
326 views

Can double-encrypting be easier to break then either algorithm on its own?

As was pointed out in Martin Bonner's comment I cannot prove this, but it seems intuitively impossible. An encryption function is supposed to obscure the plaintext to the point where no information ...
0
votes
1answer
33 views

Unicity-distance of Playfair

Given the classical scheme Playfair, say, for 5*5 matrices, I am interested to determine its unicity-distance. How should one proceed to properly do that? I should appreciate it, if I could obtain a ...
0
votes
0answers
23 views

MISTY1 encryption/ extension tricks

I'm trying to understand MISTY1 encryption algorithm but i faced some problems in key scheduling part : Key scheduling part consists of the following operations. for i = 0, ..., 7 do EK[i] = ...
0
votes
1answer
24 views

Uniqueness of checksums using DES-MAC encryption?

I'm in an Intro to Computer Security class, and one concept I'm having trouble understanding is how two different files could produce the same checksum. How would you produce the same checksum given ...
1
vote
0answers
32 views

Simple application of verifiable random function?

I have been reading a little bit about verifiable random functions (e.g.). In the literature, these are described as "pseudo-random functions that provide a non-interactively verifiable proof for the ...
1
vote
0answers
19 views

Which protocols / file formats use CBC with a random IV and without a MAC?

Disclaimer: I am a noob so this may well be a stupid question or one that's been asked before. I didn't see it come up after searching, though, so I'm going to assume it hasn't been asked here. The ...
0
votes
1answer
39 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 ...
1
vote
1answer
52 views

Testing implementation of cryptography algorithms: Brainstorm

I wonder what kind of techniques can be used to validate implementation of cryptography algorithms? The obvious one is to run specific algorithms against publically known test vectors (i.e. from ...
3
votes
1answer
96 views

Anonymity problem after voting with blind signatures

In a distributed voting system (all the messages are public, but signed and maybe encrypted/blinded), having: $d$, $e$, $N$ — registrar key params $m$ — msg $r$ — random blinding factor $m'$ ...
0
votes
1answer
38 views

Three-Pass Protocol number theory

I've got a homework problem that I'm having a hard time understanding. It's for the Three-Pass Protocol, and we are given p, the three messages, and are told that the original plain text is one of two ...
1
vote
0answers
57 views

DGHV Bootstrap - How can I recrypt my cipherbit [closed]

I'm implementing this homomorphic crypto-system : http://eprint.iacr.org/2011/440 I'm using SAGE math. I don't get how the bootstrap is done in this scheme, in the appendix A, they say ...
0
votes
2answers
72 views

Which encryption is recommended for own messenger [closed]

I wrote my own messaging-app and now I would like to encrypt the data transfer between my client (app) and my server. What kind of encryption is easy to implement and can be recommended? I am very ...
0
votes
0answers
16 views

Implications of pattern in finial digit of prime numbers [duplicate]

http://qz.com/639452/mathematicians-are-geeking-out-about-a-bizarre-discovery-in-prime-numbers/ What are the implications of this (very) new research on crytopgraphy? I would have thought this would ...
6
votes
2answers
90 views

Which attacks are possible against raw/textbook NTRU encryption?

In the same fashion that these questions about attacks to textbook RSA and ECC, I was wondering what are the immediate drawbacks of applying NTRU Encryption directly, without any padding scheme, such ...
6
votes
3answers
833 views

AES key reuse and guessing the key

Bit of a noob question and a fair bit of Googling didn't help. I understand that the current encryption standard is AES256. A few questions Is the point of this (and other encryption techniques) to ...
1
vote
1answer
32 views

Playfair Cipher Confusion with one column encryption

Recently I decided to learn "Playfair Cipher", and I have hit a road block. what do i substitute the letters for if they are on the same column? Here is an example: ...
4
votes
4answers
174 views

Is it better to encrypt before compression or vice versa?

Is it better to encrypt a plain text file before compression, or vice versa?
0
votes
1answer
66 views

Why does AES ciphertext entropy always close to 8?

I have three binary files: 31744 byte length (1), 5712980 byte length (2) and 10806008 byte length (3). The alphabet is all 256 symbols from 00 to ff. I compute the shannon entropy, replacing ...
4
votes
0answers
40 views

Best differential characteristic for this PRF

Consider the following construction of a PRF $F: \{0,1\}^{128} \times \{0,1\}^{64} \to \{0,1\}^{64}$ on 64-bit messages and 128-bit keys. Define $f:\{0,1\}^3 \to \{0,1\}$ by $$f(c,x,y) = ...
1
vote
0answers
72 views

“Prime conspiracy”'s effect on cryptography [duplicate]

Recent news reported about the discovery of a "Prime Conspiracy" which can be read about here. In summary, researchers have discovered that the last digit of prime numbers have a greater ...
0
votes
1answer
47 views

Encryption using two keys

Suppose we have two secret keys K1 and K2, I'd like to ask if there is any encryption scheme that allows us to derive another key K12 from K1, and K2 and for a message x, EK12(x) = EK1(EK2(x)). EK(x) ...
16
votes
2answers
2k views

Why is Pearson hash not used as a cryptographic hash?

The original algorithm produces 1 byte long hash and is (of course) not suitable for cryptography use. But according to wikipedia, it is possible and easy to produce Pearson hash of any length, ...
2
votes
1answer
84 views

Is there an asymmetric algorithm that can perform double encryption?

I'm looking for any asymmetric algorithm can perform the serial encryption, by serial I mean double or more encryption with different key(same key size). RSA can not do it since the cipher of the ...
3
votes
1answer
56 views

Asmuth-Bloom's threshold secret sharing scheme

I was learning Asmuth-Bloom's threshold secret sharing scheme. I was working out an example as given in this Wikipedia article. As per the example, the secret,d is 2, the number of shares, n is 4 and ...
0
votes
1answer
32 views

Sum of digits flaw name request

Let's say I am making an encryption algorithm, and in the algorithm in have the following step: "multiply the integer from the previous step by 9 and take the sum of the digits of the resulting ...
4
votes
1answer
108 views

What is Deterministic Authenticated Encryption?

I came across something known as deterministic authenticated encryption in my studies and a lot of people were associating it with Synthetic IV mode. I am having trouble what exactly DAE is because I ...
0
votes
0answers
30 views

Key diversification is a good alternative?

This is just a concept question that I need to clarify, I know that you can use key diversification as an alternative to store different symmetric keys in a database. Key diversification uses a ...
46
votes
3answers
758 views

Do these new insights into prime numbers affect encryption security?

Quanta Magazine reports: Two mathematicians have uncovered a simple, previously unnoticed property of prime numbers [...]. Prime numbers, it seems, have decided preferences about the final digits ...
1
vote
1answer
91 views

Whether this PRG is secure or not

This is the question. Suppose $G$ is a secure PRG with expansion factor $\ell(n) = 2n$ such that $n$ is a security parameter. Is it always the case that, $G'\colon \lbrace 0,1 \rbrace^n \to \lbrace ...
-3
votes
1answer
52 views

Format preserving encryption

Can format preserving encryption be used for any other applications than Credit card, pan card or social security numbers? If, could you provide a few examples for my further research on the topic?
1
vote
2answers
89 views

Difference between MAC and Authenticated Encryption?

I am currently studying authenticated encryption and I was wondering if there was a difference between using a MAC and authenticated encryption. It seemed like authenticated encryption schemes use ...
2
votes
0answers
27 views

Some questions about the internals of bcrypt [duplicate]

I'm attempting to get a better understanding of cryptography and have run into some questions about bcrypt. Bcrypt relies on the blowfish cipher, which is a reversible method of encryption. But ...
3
votes
1answer
48 views

Reverse Encryption Algorithm from Decryption code

I have the code for a decryption algorithm but I'm struggling to figure out how to reverse it into the original encryption code. ...
8
votes
3answers
167 views

The internals of bcrypt

I'm attempting to get a better understanding of cryptography and have run into some questions about bcrypt. Bcrypt relies on the blowfish cipher, which is a reversible method of encryption. But ...
3
votes
2answers
122 views

Why do we need Euler's totient function $\varphi(N)$ in RSA?

After we calculated $N = p * q$, we calculate $\varphi(N)$ and use it later to determine $e$ (PR) and $d$ (PU). But why? For decryption and encryption we only use $N$ and don't need $\varphi(N)$. So ...
2
votes
0answers
27 views

Would LWE problem be still secure if error were like this $e=2e_1$?

In the Learning with error problem, if the error term $e$ from equation $b=<a,s>/q+e$ were of this kind $e=2e_1$, where $e_1$ is chosen according to the probability distribution for the LWE ...
-1
votes
1answer
47 views

Many time pad attack (XOR) [duplicate]

The question is quite similar to Many time pad attack and I was trying to rely on the top answer, but still am a bit confused, so any explanation and help will be much appreciated. Assume I have a ...
0
votes
0answers
47 views

How randomized block cipher works?

In order to prevent known plaintext attack in case of block cipher, a simple randomization technique can be used: $E(M||R)$, here $R$ is a random bit sequence which is only available to the sender.The ...
0
votes
0answers
13 views

Why does HS1-SIV not encrypt the SIV with the PMN and key?

HS1-SIV is a good nonce-misuse-resistant, two-pass, AEAD scheme that is part of the CAESAR competition. However, it suffers from forgeries if the SIV collides. It seems to me that encrypting the SIV ...
0
votes
1answer
92 views

Zero Knowledge - Who is greater?

I just encountered the term "zero-knowledge" and wanted to know more about it. I understood that there is a zero knowledge protocol between two parties to determine whether $x$ is greater than, equal ...
3
votes
0answers
84 views

Unlinkability of Merkle-Damgård hash function results

Question: Are multiple outputs of a Merkle-Damgård hash function (or specifically SHA-256, if this can only be said for a specific algorithm) on unknown data unlinkable? If yes: Can this be formally ...
3
votes
1answer
122 views

How do I attack an RSA setup where e is even?

As a challenge, we were shown an RSA setup where we have a big $n$ (617 decimal digits), $e=4$, and asked to recover three messages. (However, the messages are padded to the same length as the key ...
3
votes
0answers
30 views

What is the current encryption method used on GSM currently?

I am currently doing a mini project which sniffs GSM packets using gr-gsm and wireshark. I was wondering if anyone knows what is the name of the current encryption algorithm method used on GSM?
3
votes
1answer
61 views

Why inversion and multiplication operations are costly in elliptic curves?

There are several algorithms for efficient scalar multiplication of an arbitrary point P(x,y) by some positive integer k in elliptic curves defined over $F_{p}$ or $F_{2^{m}}$. The scalar ...
-2
votes
1answer
42 views

python v.3.4.2 cryptography systems [closed]

does anybody know how to encrypt and decrypt using python3.4 shell cos i was wondering why people have been creating cryptographic lists then inputting them into python. The lists look something ...

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