1
vote
2answers
118 views

Quantum key distribution and OTP

Why is QKD usually associated with OTP ? QKD is about key distribution, where as OTP is about using key as long as message to get perfect secrecy, can any one explain how they are related ?
7
votes
1answer
505 views

In layman's terms, how does Shor's algorithm work?

I've just been reading up on Shor's algorithm, and I find it both fascinating and baffling. I don't really understand much about it, other than that it can factor semiprimes in polynomial time. Could ...
2
votes
5answers
630 views

How to encrypt a short string and keep the length secret

I need to encrypt relatively short strings (generally less than 100 characters). If possible, I want to avoid leaking the length of these strings. How can I do that? The thing that came to my mind is ...
10
votes
2answers
2k views

Strength of multiple hash iterations?

Is it correct that increasing the iteration possibly decreases the cipher strength but increases the amount of time it would take to find the original hash values if using brute-force on a given hash? ...
3
votes
1answer
127 views

Attack by replaying messages

Assume Alice and Bob communicate over an insecure channel using one-time perfectly-secret encryption together with one-time secure message authentication code. Say Eve has the ability to eavesdrop and ...
1
vote
1answer
96 views

How to hide bit frequency of the inter-packet delays covert channel?

I encode a hidden message as different delays between packets of another data stream. My implementation now is that for each bit, if the bit is 0, a inter-packet ...
2
votes
1answer
229 views

Proving correctness of pseudorandom generator construction given existing pseudorandom generator

Say if I have a given pseudorandom generator G which takes a k-bit input and outputs a 3k-bit number. How should I show that a specific construction using this pseudorandom generator is valid? For ...
1
vote
1answer
145 views

RSA encryption input range - plaintexts that map to ciphertexts?

According to the wiki article on the RSA encryption function, the valid range of input $m$ is $0 \leq m \lt n$. However I have found that the following values of $m$ always return themselves when ...
6
votes
1answer
485 views

Why are elliptic curve variants of RSA “chiefly of academic interest”?

Yesterday I was thinking about elliptic curve variants of popular protocols/algorithms (ECDH, ECES[1], etc) and the thought occured that I had never seen an elliptic curve variant of RSA. My ...
9
votes
2answers
1k views

Salting when encrypting?

I was attending a database encryption session at a developers conference. The presenter (who was a published author on the subject) said that MS SQL Server did not support salted hashes in the ...
9
votes
2answers
3k views

What's is the main difference between a key, an IV and a nonce?

What are the main differences between a nonce, a key and an IV. Without any doubt the key should be kept secret. But what about the nonce and the IV. What's the main difference between them and their ...
2
votes
1answer
328 views

server side Javascript security

It is accepted that the javascript library lacks the ability to create an adequate PRNG. My understanding that this was mainly due to the limits of a sandboxed browser enviroment that javascript ...
3
votes
1answer
134 views

Correct method to encrypt data so that it can be decrypted only by Alice and Bob

I need to build a system that stores encrypted transactions. Transaction involves always two parties. Payer and payee. Both must be able to download encrypted transaction from server and decrypt it ...
2
votes
2answers
457 views

Calculating cycles per byte

Cycles per byte seems to be a critical concern in designing and choosing stream ciphers. For example, from Wikipedia, RC4 has 7 cycles/byte on original Pentium chips. How is this calculated? Do they ...
1
vote
1answer
117 views

Tips on conceiving safe software messaging platform

I have a personal project in mind in which I plan to use cryptography in order to let the users be confident in the fact that, even if all data get's stolen, it would be virtually impossible to crack ...
15
votes
2answers
2k views

What are the main weaknesses, if any, of a Playfair cipher?

What are the main weaknesses, if any, of a Playfair cipher? I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other ...
2
votes
1answer
169 views

How could block encryption in counter mode be secure from viewpoint of entropy?

A good block cipher e.g. AES running in counter mode is commonly considered to be secure. Assuming a perfectly random key, one could in this case from $128$ bits generate up to $2^{128}·128$ bits for ...
2
votes
1answer
343 views

What is the strength of unpadded RSA?

I would like to use unpadded RSA for homomorphic encryption in a toy P2P game, for things like fair coin flips and shuffling. How many bits of security does unpadded RSA have, in relation to its key ...
3
votes
3answers
435 views

How to avoid a chicken and egg scenario with encrypting passwords?

I am working on application that allows users to upload files containing company data and then share those files with a list of other users that have specific roles within the system. I want to ...
1
vote
3answers
315 views

How does one provide a secure and authentic communication channel?

Let assume two participants Alice and Bob who perform a given protocol which is a sequence of messages exchange between them. My question is: How can I provide a secure and authentic communication ...
4
votes
1answer
483 views

is this RSA private key valid?

is this RSA private key valid? First, here's the RSA private key in question: ...
2
votes
1answer
256 views

Exact mathematical definition of simulation based security?

I've been trying to understand cryptographic protocols and how to define their security. The problem is that while I can understand what the intuitive definition says, I have trouble understanding how ...
2
votes
1answer
583 views

How to test distribution of a hash function?

From what I've found, it is generally accepted a cryptographic hash function like SHA-2 has an evenly, randomly distributed output. Is there a way to test this without running through the entire ...
2
votes
2answers
340 views

when do we need composite order groups for bilinear maps and when prime order?

Why we need bilinear groups of composite order? What's the special security property of the composite order group in comparison with one of prime order?To put it in another way when do we need ...
1
vote
1answer
109 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
1answer
112 views

why $e(g,g)^N=1$ in bilinear pairings holds?

I can't get the point of prime order bilinear pairings:$\mathbb{G}\times\mathbb{G}\rightarrow\mathbb{G}_T$,$g=$ generator of $\mathbb{G}$ , $N=p*q$, $p$ and $q$ primes and $e(g,g)^N=1$. why ...
4
votes
1answer
782 views

Figuring out key in hill cipher (chosen-plaintext attack)

I have been wondering what approach to take in order to figure out what key was used to encrypt a message using the hill cipher. I know it is possible to obtain it even if it were just a ...
3
votes
4answers
969 views

Which is more secure using a CSPRNG for a One-time pad, or AES?

In reading about the One-time pad it appears to need truly random key for the pad. Since true random values are not practical to generate this presents a problem (thus making One-time pad less ...
1
vote
0answers
281 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 ...
2
votes
1answer
354 views

Several questions about Paillier cryptosystem

I have several questions concerning the original Paillier cryptosystem as described in Paillier, Pascal (1999). "Public-Key Cryptosystems Based on Composite Degree Residuosity Classes". EUROCRYPT. ...
4
votes
1answer
130 views

Safety of a pre-keyed DH-Key Exchange

Asuming this scenario: Bob and Alice each have the public key of the other party for a D-H function and want to exchange data. Now, if they each generate their shared secret, is it safe to assume ...
1
vote
1answer
269 views

Blowfish Encryptions in Bcrypt hashing algorithm

I am trying to understand the ExpandKey function used in the bcrypt hashing algorithm. As per the documentation of bcrypt hashing algorithm on USENIX here: ...
-2
votes
0answers
379 views

Why is there a strong distinction between stream and block ciphers? [duplicate]

If I don't err, in the literature a stream cipher is one in which each plaintext bit is processed individually, commonly via xor-ing with one bit of a random or pseudo-random bit stream, while a block ...
3
votes
2answers
7k views

FIPS 140-2 Compliant Algorithms

Is there any reference to check the list of encryption & signing algorithms which are compliant to FIPS 140-2. After an exhaustive search I could find only "AES". Any suggestions would be much ...
2
votes
2answers
2k views

Is RSASSA-PKCS1-v1_5 a good signature scheme for new systems?

Is RSASSA-PKCS1-v1_5 a good signature scheme to recommend that people use in new systems? Is it believed to be secure and represent the state-of-the-art in RSA-based signatures? I understand that ...
0
votes
1answer
205 views

How to plot the distribution of a ciphertext?

Is there any plot or visualizing program that can plot the distribution of a plaintext and then the distribution of the ciphertext after applying a ciphering encryption algorithm? I am interested ...
3
votes
3answers
11k views

Possible ways to crack simple substitution ciphers

We had a quiz in class today where we had to break the ciphertext with the key given, but not the algorithm. Suffice to say that I wasn't able to decrypt it within the alloted time of 12 mins and will ...
3
votes
2answers
2k views

How many keys does the Playfair Cipher have?

I was just studying the Playfair cipher and from what I've understood, it is just a slightly better version of a Caesar cipher, in that it isn't actually mono-alphabetic but rather the 'digrams' are ...
6
votes
2answers
555 views

Why do public keys need to be validated?

For some curves it's necessary to validate the public-key of the other side before running an elliptic-curve Diffie-Hellman key-exchange. Apparently if you don't validate the public key, small ...
2
votes
1answer
844 views

Shortcuts / practicality of brute forcing block cipher (AES) + ECB with known plaintext

I know the plaintext (26 bytes long) and cryptotext of block cipher (suspected to be AES) in ECB mode. I can generate hundreds or thousands of such samples, but the samples are not arbitrary. What are ...
3
votes
1answer
87 views

Data-validating protocol

I have to implement protocol of secure data transfer that can be described as Alice selects data to send from finite set $m\in M$ (e.g. $M$ could be a column of values in database table) Alice ...
3
votes
1answer
102 views

Is the mod_auth_tkt scheme secure?

The third-party Apache plugin mod_auth_tkt uses a tragically-not-HMAC construction: ...
6
votes
2answers
296 views

What is a “rewinding argument”?

I've been reading a bit about cryptographic protocols and I keep seeing the phrase "rewinding argument". I've been unable to find a good source that would explain what is meant by this. It seems like ...
0
votes
1answer
610 views

How to implement order preserving encryption or order preserving hashing [closed]

Does anybody know any free implementation of either order preserving encryption or order preserving hashing? I've found some codes like CMPH but I need to dynamically add new DATA and that's why most ...
10
votes
1answer
753 views

GPG/PGP Verification of Revocation

How does one verify a key revocation? After revoking a key and sending the revocation to MIT's keyserver, I noticed that the key is listed as such: ...
3
votes
2answers
325 views

Encryption scheme with equivalent keys?

I've long been looking for a symmetric encryption scheme (or algorithm) with equivalent keys. Let me define what I want: Symmetric encryption algorithm with encryption function $E_k$ and inverse ...
4
votes
1answer
89 views

Dimension of Encryption of a linearly dependent set of plaintexts

Suppose I have an encryption scheme of the form $ E(P)=C $ where $P$ is the plaintext and belongs in $\{0,1\}^N$, $C$ the ciphertext which belongs to $\{0,1\}^M$ and the encryption is performed under ...
0
votes
3answers
202 views

fixing WEP by treating all messages as one long stream

in the course of introduction to cryptography on coursera professor suggested treating all messages as a long stream XORing them with the key this way we will not need to change the key and will not ...
2
votes
1answer
910 views

BouncyCastle Elliptic Curve implementation

I'm implementing ECDH key exchange in C# using the BouncyCastle library and I'm having a hard time understanding the elliptic curve side (FpCurve). ...
10
votes
2answers
666 views

Why RSA can't handle numbers above 76?

I'm going to encrypt the characters Zhu, and decrypt them using RSA. I'm using the public key $\{e, n\}$ and private key $\{d, n\}$. The values of $e$, $d$ and $p$ ...

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