1
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0answers
174 views

Sigma-protocol for 3SAT problem

I have some questions from previous years exams, I hope you could help me with them. :) Let $g,h$ denote generators of a group $G$ of large prime order $n$ such that $\log_g h$ is unknown to anyone. ...
1
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0answers
127 views

Quadratic Sieve Bottleneck, Multiple Polynomials an option?

After my failed attempt at trying to implement the ECM, I started working on the quadratic sieve. It works, but the bottleneck is finding smooth values over the factor base. The way I implemented it ...
1
vote
0answers
85 views

Why do we always append padding bits in SHA-512? [duplicate]

Possible Duplicate: In the SHA hash algorithm, why is the message always padded? I'm reading the book Network Security Essentials written by William Stallings. To create a message digest ...
1
vote
0answers
56 views

IND-CPA security scheme [duplicate]

Possible Duplicate: CPA Secure Chosen plaintext scheme The example for IND-CPA secure schemes given is generally: for a random r, $Enc_k(m) =(r|| E_k(r)$ $XOR$ $m)$ where $E$ is a $PRF$ ...
1
vote
1answer
118 views

WebcryptoAPI - secure or not [closed]

This is about the new W3 WebcryptoAPI draft standard. Here is a post by one of it's authors https://plus.google.com/u/0/105761279104103278252/posts/CSwVZ1RUijo It says its in part trying to change ...
1
vote
0answers
374 views

Stream Cipher : Never use stream cipher key more than once [duplicate]

Possible Duplicate: Taking advantage of one-time pad key reuse? How does one attack a two-time pad (i.e. one time pad with key reuse)? Denote C is cipher text, m is message, and PRG(k) is ...
1
vote
0answers
111 views

Timestamping services authorities, utilizing Linked, hybrid and other than PKI schemes

What are well respected Cryptographic Timestamping authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), ...
1
vote
0answers
202 views

Is TOTP or a timestamp encryption a better timestamp-based authentication token system?

Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
1
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0answers
196 views

Proper formatting of symmetric algorithm secret key

Given this description from RFC 4880 sec 5.1: The value "m" in the above formulas is derived from the session key as follows. First, the session key is prefixed with a one-octet algorithm ...
1
vote
0answers
75 views

Applying multiple hash functions to improve security? [duplicate]

Possible Duplicate: Guarding against cryptanalytic breakthroughs: combining multiple hash functions I'm a total newb to cryptography but after reading what I've read about it, I had a ...
1
vote
1answer
205 views

NTRUEncrypt - Choose the initial random polynomial

I'm trying to implement NTRUEncrypt but encounter some problems. I've finished all the basic functions that are needed for the scheme base on this Document, but I can't find an algorithm to check the ...
1
vote
0answers
61 views

cipher text only attack - how to know when to stop when brute-force attack? [duplicate]

Possible Duplicate: How can I do a brute force (ciphertext only) attack on an CBC-encrypted message? My question is about a cipher text only attack - I have as input only the initialization ...
1
vote
0answers
221 views

Most frequently used digital signature schemes in the recent years

I am looking to understand if there are any hard figures on which digital signature schemes are most commonly in use today. I'm only really interested in what is employed recently (ie. last couple ...
1
vote
0answers
74 views

Is it possible to build an unfair noisy channel from 1 out of 2 oblivious transfer [closed]

For a fair channel, sender sends a bit b and receiver gets it with probability 1/2 and gets b's flipped value with probability 1/2. It is trivial to build a fair noisy channel from 1 out of 2 ...
1
vote
0answers
343 views

Diffie hellman key exchange on elliptic curve over an extension field [closed]

I am attempting to do a final semester project where I implement Diffie-Hellman key exchange on an elliptic curve over an extension field (2^256). Can anybody help me to generate the extension field ...
1
vote
1answer
266 views

ZKIP for Paillier public key correctness

I'm using the Paillier cryptosystem in a protocol similar to mental poker. In the beginning of the protocol, each player generates a Paillier public key $(n,g)$. Later in the protocol, a player may ...
1
vote
0answers
80 views

Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]

Possible Duplicate: Two untrusted party want to exchange data: how to insure each one gets the data it needs? I am trying to come up with what could maybe be a novel algorithm for an ...
1
vote
1answer
59 views

Standard serialization format for libsodium-based messages

Does anyone know of a standardized serialization format which can be (or already is) widely used for encrypted messages? For a variety of reasons (mostly complexity, age and poor support across a lot ...
1
vote
2answers
145 views

Given infinite unencrypted and encrypted texts, can I find the algorithm?

Given an infinite amount of both unencrypted and the corresponding encrypted text, would I be able to calculate the algorithm? I am relative new to cryptography and don't know if I would be able to ...
1
vote
1answer
67 views

What is the difference between IND-CCA2 and NM-CCA2? And how does one imply another? [closed]

Is there any proof that shows the equivalence of these two?
1
vote
1answer
147 views

Block cipher to encrypt 8 bytes/64 bits - Use 64 or 128 bit cipher?

Here's the problem: I have a transport stream that I have been requested to encrypt between the transmitter and receiver. The data size is at most 8 bytes so it seems I can only use ECB as I only have ...
1
vote
1answer
171 views

problem with “one time pad” [closed]

I am a french student and I read the post on the forums (How does one attack a two-time pad (i.e. one time pad with key reuse)?). I need your help if possible. I 'm 11 encrypted messages , all ...
1
vote
2answers
105 views

what is PFS game?

when i reading about this paper, in the Setup of SIM section 5.2, it says that "According to the definition of PFS game", i wonder what the definition of PFS game ...
1
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2answers
227 views

Is there a theoretical maximum useful keysize given the block-size?

Consider a block-cipher $F$ with a $N$-bit block-size and a $M$-bit key-size. That is, if $k$ is a $M$-bit key, $p$ is a $N$-bit block of plain-text and $c$ is a $N$-bit block of cipher-text, then: ...
1
vote
1answer
115 views

Hash function as secure as one-time pad?

We know that the one-time pad is provably secure as a cipher to encrypt some data. Is there an algorithm which does the same just as a hash function? Can we get a provably secure hash function? Maybe ...
1
vote
1answer
90 views

Is there a kind of OS entropy pool on Windows systems? [closed]

I am wondering if Windows provides an equivalent of /dev/urandom from linux ? Or any kind of system entropy pool ?
1
vote
2answers
131 views

Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
1
vote
2answers
382 views

Is it possible to generate a 6-digit number using 256-bit encryption?

Reading through some documentation on a piece of software, it claims that a 4-6 digit number is created using a 256-bit encryption process for the purposes of access control. The whole process works ...
0
votes
4answers
2k views

Is a Mersenne-twister cryptographically secure if I truncate the output? [closed]

I want to create an online roulette game. Is it OK if the PRNG is seeded only once, when the user starts the game, or is it recommended to re-seed sometimes during game? Maybe just seeded once a day ...
0
votes
4answers
512 views

Is the One Time Pad (OTP) considered a cryptographic hash function?

As the title states, would the One Time Pad (OTP) be considered a cryptographic hash function?
0
votes
3answers
884 views

Does knowing common prefixes help crack blowfish?

I have strings that are if the form: {static data}{changing data} The beginning static data part is around 20 characters and is common to all strings. The last ...
0
votes
2answers
256 views

How secure would this code be against cryptanalysis?

Simple version: Create software that takes a database of the dictionary, alphabet, and phrases. Randomly generate a database of random strings of letters/numbers/symbols of varying length. Randomly ...
0
votes
2answers
202 views

DES generating the same ciphertext for different plaintexts and identical key

Is it possible to get the same output for DES while the inputs are different while using the same key? The key should not have to be a weak key. If yes could you give me a hint how to show how to do ...
0
votes
2answers
238 views

Why are these techniques not feasible to crack RSA?

For $d = e^{-1} \mod \phi(n)$ $$d\cdot e \operatorname{mod} \phi(n)=1$$ $$d = (e^{-1} \operatorname{mod} \phi(n))$$ With having $e$ and $n$, we can calculate the value of $d$ , the private key for ...
0
votes
3answers
214 views

Is there a way to break this encryption?

I was wondering about making up a simple system to encrypt a file: ...
0
votes
3answers
385 views

Security of very simple XOR with random? [duplicate]

I am currently trying to implement a very fast and simple encryption algorithm in Lua for the purpose of using it with ComputerCraft. The main problem is that bitwise operations in Lua (5.2 at least) ...
0
votes
2answers
958 views

RSA PCKS1 v2.1 RSAES-OAEP algorithm

Using RSA public key (n,e) the encryption of a message is c= (m^e) mod n and the corresponding message is decrypted as ...
0
votes
3answers
1k views

Is AES really used for Top Secret stuff?

I've read almost everywhere that AES-256 can be used for Top Secret material (in the US). Is it really used or is it some kind of decoy to hide the more advanced algorithm they might use ?
0
votes
3answers
422 views

What block cipher is used for CBC-MAC?

What block cipher is used for CBC-MAC? DES, AES, 3DES? Or it doesn't matter?
0
votes
1answer
50 views

Is it safe to encrypt data by simply randomizing chunks based on a permutation?

Say I want to encrypt the following text: "Today is March the 22nd, 2015". And say want to encrypt 8-byte blocks of data using the following permutation [6,3,0,1,5,7,2,4] to swap characters at those ...
0
votes
3answers
186 views

When is a cipher considered broken?

We've all read how some people claim AES is broken because there was supposedly a way to get the plain text from a cipher text faster than brute-force. But is this the definition? Is a cipher broken ...
0
votes
1answer
77 views

Is there any definition for “generic attack” in context of cryptography or more specific “hash functions”?

I'm searching a definition of "generic attack" in context of cryptography or more specific in context of "hash functions". I searched some books and the web but I did not found any definition for it ...
0
votes
1answer
123 views

Why is DDH not hard over $\mathbb{Z}^*_p$?

Why is Diffie-Hellman key exchange not hard over $\mathbb{Z}^{*}_p$?
0
votes
3answers
304 views

Can you help me with this Random Number Generator function?

By someone's suggestion, I am posting this question from math.stackexchange.com. I want to find out a suitable function or algorithm, which can provide a random sequence like this… Input: $3$ ...
0
votes
2answers
113 views

Asymmetric encryption that is secure for (almost) any foreseeable future

Recently, I've been reading a couple of papers about building cryptosystems that are secure for up to 30 years. But for some applications, this seems a bit low to me. So I am wondering if considering ...
0
votes
2answers
102 views

Removing “security by obscurity” from port knocking

Every article about port knocking, for instance https://wiki.archlinux.org/index.php/Port_Knocking , declares this method as security by obscurity. Is the following enough to remove that title; a ...
0
votes
3answers
128 views

Known plaintext, unknown 128 bit block cipher

I have an encrypted configuration file from an embedded device which I'm trying to decrypt. The file seems to be encrypted in 128bit blocks, as changing a single option causes a 16 byte block to ...
0
votes
2answers
92 views

Will SHA1 or Other Hash Functions Ever Contain Quotes [closed]

I feel foolish asking this, but will the hash generated by SHA-1 or other encryption methods ever have the possibility of containing a quote? Or any other characters that may be escaped such as ", ', ...
0
votes
1answer
154 views

Why does the DES crypto algorithm NOT use 2 rounds?

Now, if we were to go round by round, you could give a distinct reason for not using a single round since after just one round, the right half of the text comes directly, as-is, to form the left half ...
0
votes
2answers
150 views

Factors of RSA modulus

In the article A Method for Obtaining Digital Signatures and Public-Key Cryptosystems, the original RSA article, it is mentioned that Miller has shown that n (the modulus) can be factored using any ...

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