# All Questions

1answer
240 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 ...
0answers
79 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 ...
1answer
55 views

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

Is there any proof that shows the equivalence of these two?
1answer
67 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 ...
2answers
218 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: ...
2answers
303 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 ...
4answers
1k 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 ...
4answers
458 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?
3answers
812 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 ...
2answers
246 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 ...
2answers
224 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 ...
3answers
206 views

### Is there a way to break this encryption?

I was wondering about making up a simple system to encrypt a file: ...
3answers
161 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) ...
2answers
688 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 ...
3answers
845 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 ?
1answer
62 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 ...
1answer
109 views

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

Why is Diffie-Hellman key exchange not hard over $\mathbb{Z}^{*}_p$?
2answers
512 views

### Can a salt for a password hash be public?

For my understanding salts in password hashes are used to prevent the precompuation of plaintext$\to$hashvalues (rainbow tables). I know from different threads, it is not necessary to keep the salt ...
3answers
209 views

### Alternative to NSA encryption algorithm

I am looking for a strong alternative to elliptic curve cryptography. It should be something that could face quantum computing attacks, but nothing created by the NSA. I heard about isogeny key ...
3answers
1k views

### AES256-CBC vs AES256-CTR in SSH [duplicate]

I used AES256-CBC to SSH to a remote server. Recently, it stopped working with the following message: ...
1answer
422 views

### Random Number Generator based on AES CTR

I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. Here's the link to the project, hosted at codeproject.com. It is written in ...
2answers
173 views

### Pi Message Encryption [duplicate]

I created a simple yet efficient message encrypting page that will encrypt messages using Pi. Though not being an expert in this area, I am nowhere near sure how secure this is and how easy it would ...
3answers
189 views

### Are hash functions chaotic?

I'm looking into "bitcoin like" mining processes. Say a security process uses a hash of data as proof that the data was known at some point in time. From what I understand, hash functions are ...
2answers
152 views

### Why is ElGamalEngine in bouncy castle restricting input data to be less than the length of the group parameter p?

I am currently using the ElGamalEngine of bouncy castle to implement exponential ElGamal for the purpose of making ElGamal additively homomorphic. To do this i raise the message to be encrypted to the ...
3answers
331 views

### Generating a number using SHA512 that users can later verify (once I publish secret seed)

I've wrote following C# method that basically takes 3 seeds and gives you number in 0-100 range. I then use that number for variety of purposes but for this question the most important one is the ...
2answers
159 views

### Encryption of a number with RSA bigger than $n$

I'm having trouble understanding why encrypting a number $m$, which is larger than $n=p\cdot q$. I've looked into the following threads: Why RSA can't handle numbers above 76? Why does plain RSA ...
2answers
117 views

### Why use two affine transformations in Multivariate Cryptography?

I'm reading Multivariate Cryptography and would like to know why we use two affine transformations to scramble the central map? Why not use only one?
2answers
245 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?
2answers
376 views

### One Time Pad Question

I have a ciphertext encoded with One Time Pad. I do not know the key. How can I find the possible keys which when decoded, will result in a meaningful plain text?
2answers
97 views

### A substitution based on a matrix vector product

I choose at random an invertible square matrix A of size 128 in GF(2). I want to use this matrix as a substitution box. Is this a non linear transformation ? I've seen that substitution boxes are ...
1answer
464 views

### True 128bit secured password length?

assume we say 128bit keys are secure so a 16 character long password is safe, but if i even use lower case and upper case letters with numbers and special characters on my keyboard its about 80 ...
2answers
273 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: $3$ ...
1answer
79 views

I am currently studying Diffie-Helman protocol. In my lecture notes I have a generator g=2 and I'm in group $Z_{13}^*$ . There I calculate a remainder cycle from 1 to 12 with $r =g^i \mod 13 \forall ... 2answers 36 views ### Bouncy jdk 1.51 Serpent KAT tests vs Nessie vectors Having a little trouble getting Nessie vectors working with the Bouncy Castle SerpentEngine. Do the Nessie vectors require a mode or some pre-processing? Nessie Serpent 128, set 1, vector 0 reads: ... 2answers 54 views ### Are all block ciphers FPE (format preserving encryption)? A FPE preserves the format. There is a correspondence between the format of the ciphertext and the plaintext. Given that a message in some binary enconded format can easily be divded in some ... 2answers 163 views ### Strategy to crack a presumed substitution cipher The ciphertext given is: ejitp spawa qleji taiul rtwll rflrl laoat wsqqj atgac kthls iraoa twlpl qjatw jufrh lhuts qataq itats aittk stqfj cae I've done ... 2answers 168 views ### Why are Fortuna entropy pools reset after a reseed? I've implemented LibTomCrypt's version of fortuna and am wondering about the pool resetting after a reseed. In fortuna.c in libtomcrypt we have the following (which is that part that adds the entropy ... 2answers 163 views ### Wrong Test Vector for HKDF with HMAC-SHA256 [closed] I have implemented HKDF by myself and it seems to work good. I managed to replicate all the test vectors listed here but... except this one: ... 2answers 83 views ### Times of nested algorithms in proofs of security Proofs of security may be constructed such that an adversary$A$is used to construct an adversary$A'$. The reduction/algorithm which uses$A$has to perform a number of computations in order to ... 2answers 247 views ### Should an AES byte key generated with OpenSSL be converted to hex? I am generating a key & iv with Ruby's OpenSSL wrapper for an AES CBC 256 setup: ... 2answers 97 views ### Needed: signature over a collection of hashes I'm looking for some kind of crypto-based data structure that will allow me to produce a signature over a set of hashes. Call this a SignedSetOfHashes. I want to be ... 2answers 555 views ### FIPS 140-2 compliant algorithms in Enhanced RSA and AES Cryptographic Provider (Windows XP) [closed] We have a native C++ application that supports Windows XP SP3. Recently we've decided to change our crypto algorithms to FIPS 140-2 compliant ones. We are planning to use the following algorithms in ... 2answers 189 views ### Regex searchable word list for space-less monoalphabetic substitution [closed] I am working on teaching myself basic cryptography, in the process I created a simple substitution cipher based on a single alphabet, and a statically defined offset (no key for now). Now that ... 1answer 172 views ### What is the difference between, and security of$Z_p$and$F_p$? While reading some papers, I found that sometimes$Z_p$was used but sometimes$F_p$was used ($p$is prime). Usually, the author will only use their subgroups like this: choose a big prime factor of ... 1answer 335 views ### Is this encryption scheme perfectly secure? Let$m = 6$, and let$\mathbb{Z}_m$denote the set$\{0,…,m-1\}$. Let$X \mod m$denote the remainder obtained when dividing$X$by$m$. (a) Consider the symmetric encryption scheme in ... 3answers 210 views ### Why not just generate random strings for one-time password (OTP)? http://en.wikipedia.org/wiki/One-time_password#How_OTPs_are_generated_and_distributed Why have so many methods to generate OTPs, why not just use just random strings? 2answers 898 views ### HMAC vs Encrypted Hash What is best to use (for message integrity) between… AES(Data) + HMAC(Data) AES(Data + HMAC(Data)) AES(Data + Hash(Data)) …and why? 2answers 129 views ### Key Refresh in Diffie-Hellman Assume the case, that two participants have agreed on a key$K=g^{ab} \mod p$via Diffie Hellman. I have the need to change the key every now and then. The first idea I had was to simply initiate a ... 2answers 166 views ### Is there a way to encrypt multiple sets of data into one result, with separate keys decrypting each set of data What I am picturing is something like this: Block A: "Hello, how are you today?" Block B: "The weather reminds me of summer." I encode this, giving me two keys and a resulting encrypted block e.g. ... 1answer 342 views ### Is this scheme a provably fair random number generation? I have thought up a method for generating random numbers between a client and a server which I hope is fair: The client and server decide on a range in advance,$0$trough$n-1\$. The server ...

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