# All Questions

208 views

### Secure Secret sharing

I'm trying to come up with a new way to do oblivious transfer that is faster and requires less computation than existing methods. The basis of my method is shamir secret sharing. Below is an example ...
173 views

### Autocorrelation in Autokey

I know that Vigenère can broken using auto-correlation (as explained at cryptool-online.org). Now my question is: Why does this also work with autokey (tested it using crypttool)? To prove that I ...
91 views

### Does $i^n=j^n$ for $i, j \in GF(2^q)$ and $i \neq j$ for some $n<2^q-1$

Let $i, j \in GF(2^q)$ and $i \neq j$ and $i,j\neq0$. Is that possible that $i^n=j^n$ for some $n$ such that $0 < n < 2^q-1$? I am looking for a proof if the answer is no, or for a method to ...
514 views

### Smart Card Basics

I want to implement some of the basic encryption algorithms on smart card, could any body guide me how to program a smart card, which tools (hardware and software) I should have, and if these tools ...
66 views

### How small are we talking about when defining the small public/private key exponent [duplicate]

I've been wondering about the 'small' part of the attacks on RSA, like the small public key exponent and the small private key exponent and what's not really clear is how small are we talking about? ...
340 views

### Construct an encryption algorithm using hash function [duplicate]

We know that Cryptographic hash function is generally a one-way function where we can't retrieve the original message. On the other hand, encryption is a two-way-function where we get the original ...
370 views

### Tactics available to help prove security of a new system?

I believe that the accepted tactic to "prove" a system as secure is to allow the crypto-community to review it and if no vulnerabilities are found over a long period of time (5 or 6 years), then a new ...
2k views

### Decrypting Triple-DES using 2 keys in crypto tools

I'm currently working on crypto tools to encrypt/decrypt 4 blocks of messages using Triple-DES with 2 keys. So, I've reached the final cipher text, but now I have to do the reverse and get the ...
307 views

### Pailler and Gentry - homomorphic encryption

Paillier cryptosystem is a probabilistic asymmetric algorithm for public key cryptography. Doesn't homomorphic encryption schemes have regular effects on the plaintext, and does that mean Pailliers ...
42 views

### Can anyone explain how the modified r-adding walk works?

I was going through a paper titled “Accelerating Pollard's Rho Algorithm on Finite Fields” by Jung Hee Cheon et al. I understand the table(Ml) creation part of it, but after that I somehow fail to ...
138 views

### Blowfish vs. Twofish regarding power consumption

If I wanted to use Blowfish or Twofish to provide security on a device where power consumption is crucial. Regarding power consumption, which one would win? Generally, which algorithms are known to ...
59 views

### The improvement of the private key exponent in the M.Weiner Attack

I am working on attacks on RSA and came across the M. Weiner attack. The limit for $d$ in order for the attack to apply is $d <= (\frac{1}{3})N^{0.25}$. The paper states that Boneh and Durfee ...
227 views

### Illustrate NTRU using lattices

I studied some papers related to NTRU. All these papers describe NTRU as a lattice based cryptosystem but I could not find any paper which illustrates NTRU algorithm from lattice point of view. It ...
86 views

### Looking for crypto with derived keys?

I am looking for cryptographic algorithm or combination of them. Basically I need an algorithm, which can generate private key and for this key can be computed multiple keys based on some seed. So a ...
72 views

### Want to use ECC but am clueless [closed]

First off, I'm not an experienced cryptography or computer person, please bear with me. I have some basic experiences with PGP software though (not much of a redemption huh?). I have some data that ...
311 views

### What's the advantage of using OFB/CFB/CTR modes over a stream cipher

As far as I understand: The primary disadvantage associated with stream ciphers is the need for a random and unique key for each run in order to protect against reused-key attacks. OFB/CFB/CTR block ...
153 views

### how much trust can we place in protocol verifiers? [closed]

I read many papers on authenticated key exchange protocols, and most security proofs are done by the authors. In this method, you can imagine that the efficiency is low. Moreover, even if you have ...
112 views

### Need to generate new DH keys for every message in OTR

Going through the OTR specification I don't quite get why a new DH keys (and hence new symmetric key and hmac key) are generated for each message to be sent. Why is this necessary? I don't think it ...
469 views

### Uniform distribution/randomness of characters in the sha256 hash?

I'm using the sha256 algorithm to generate a number in one of my programming projects. A sha256 hash is calculated from three strings: one the user can edit, one the user can view but not edit and one ...
154 views

### How to handle the GCD(V,P) != 1 case when doing point addition or point doubling in elliptic curve cryptography

The equation for a finite field Elliptic Curve is of this form: $$y^2 \equiv x^3 + a * x + b \pmod{P}$$ When we do common EC operations like point doubling or point addition we need to calculate the ...
425 views

### Analyzing ECB's and CBC's resistence to a known-plaintext attack

I'm trying to analyze the strength of a block cipher with CBC mode or with ECB mode on the scenario of an exhaustive search attack with knowledge of pairs of plaintext – ciphertext (known plaintext ...
206 views

### KDF followed by a Hash?

It is my understanding that a KDF adds entropy, whereas a hash loses information. I've read that KDF should be used to store passwords. I don't understand why we don't use a KDF and then a hash, so ...
795 views

### RSA and ECDSA performances

Signature algorithms with elliptic curves have small output sizes compared to RSA for the same level of security. What about the processing time to generate a signature ? I've seen figures giving ...
50 views

### Common pitfalls of session key activation?

Assume that initiator $I$ and responder $R$ of a key agreement protocol have agreed on new symmetric session keys $K'_{auth}$ and $K'_{enc}$, e.g. by way of Diffie-Hellman and key derivation, possibly ...
229 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 ...
498 views

### IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG? [closed]

I am using a AutoSeededRNG from Crypto++ to generate IVs for use in CBC encryption. I am encoding the IVs using Base64 for future use (decryption). I notice that ...
213 views

### Any techniques for evading frequency based crypt analysis without encrypting?

Are there any general techniques for evading frequency based crypt analysis without using any encryption techniques?
301 views

### Is there a “brainwallet” for GPG keys? [closed]

“Brainwallet” is a program that takes a passphrase (hopefully a good one) and deterministically creates a Bitcoin wallet. This wallet can be used for transactions, then deleted from the computer. To ...
259 views

### Does ECIES imply authenticity?

Assume: Alice and Bob both generate separate EC keypairs Alice obtains Bob's public key, and together with her private key creates a shared secret key Alice encrypts a message using the shared key ...
638 views

I'm relatively new to encrypting, and I have some questions. I intend to write a standalone C# program that will write and read an encrypted file with sensitive data using a password entered by the ...
1k views

### Is there an intuitive explanation as to why only the private key can decrypt a message encrypted with the public key?

I have just learned about using PGP/GPG for email encryption and one thing has always bugged me: How is it possible that a message encrypted with somebody's public key can be decrypted only with that ...
466 views

### Does data authenticity always, implicitly, provide data integrity?

Does a scheme which provides data authenticity (e.g. HMAC or RSA signature) always implicitly provide integrity? It seems, to me at least, that it must by necessity. However, I have seen ...
2k views

### Is sharing the modulus for multiple RSA key pairs secure?

In the public-key system RSA scheme, each user holds beyond a public modulus $m$ a public exponent, $e$, and a private exponent, $d$. Suppose that Bob's private exponent is learned by other users. ...
59 views

### For enciphering messages with AES in CTR mode, do I need a different key for each message?

I have written a program to run AES in CTR mode with keys of 128,192 or 256 bits and checked it gives correct results with the data given in section F.5 at ...
92 views

### (n,n) Shamir secret sharing [duplicate]

In (n,n) Shamir secret sharing if n shareholders do not have the public values (X values) can they still obtain the secret with only Y values?
170 views

### Error propogation in CBC mode

Going through the wiki for modes of operation I see that the section error propogation says that an error in one block in the ciphertext in CBC mode only impacts two blocks. I do not quite get that. ...
1k views

### Generating Encryption Keys from Biometric Fingerprint Templates

How would one go about generating Encryption Keys from Biometric Fingerprint Templates extracted from a fingerprint using either Griaule SDK or DigitalPersona SDK or any other SDK that will return the ...
70 views

### Problem with anonymously merging information from distributed sources

Some Background: There is an entity with an identifier and some information. The identifier of this entity is a string with a known scheme/pattern(Which means the total number of such possible ...
82 views

### Pairing Field size as security parameter

I have read Pairings for cryptographers: It states that the groups $G_1$ and $G_2$ are groups of points on the curve and the group GT is a subgroup of the multiplicative group of a related finite ...
82 views

### Is there an anonymous non-interactive authorisation scheme with peer-side auth. signature generation?

I implemented a pseudonymous PKI scheme (by K. Zeng @Springer Link), where all peers can change their public keys including its signature on their own. I am looking for a way to extend it with some ...
312 views

### Is there a public-key cryptography method that enables public keys to be much smaller than private keys?

Does a public key cryptography method that enables the public key to be orders of magnitude smaller than the private key exist?
84 views

### order of elliptic curve divisible by prime

Why order "u" of an elliptic curve "E" defined over a finite field "GF (q)" (u = | E / GF (q) |) must be divisible by a large prime number r to be appropriate for cryptographic purposes?
93 views

### Why would splitting a password output be better than separate HMACs for encryption/authentication key derivation?

In a recent question I asked here on crypto.se, an answer was given that surprised me a bit. As mentioned in the referenced question, I'm looking to derive encryption and authentication keys from ...
208 views

### How can I perform matching on an “encrypted- fingerprint feature matrix” using Fully Homomorphic Encryption?

I am doing a finger-print authentication process. The feature-extraction using minutiae has been done and I get an N x 6 matrix, where the 6 columns are {$x_i$ ...
112 views

### How does this SSL-related flaw work?

I just saw a video at CNN in which it is claimed that, if the server isn't generating a random public key, the server can be hacked. First how HTTPS works… to be sure I’m on the same page: Server ...
378 views

### ECC Complexity order of point addition, scalar point multiplication and selecting random point

I am facing this problem in calculating the order of a process which involves ECC point addition: $P+Q$ , scalar multiplication: $aP$, and selecting random points in the group. The group is of prime ...
118 views

### Journals to read in order to keep up to date with interesting research [closed]

I'd love suggestions from crypto.stack as to academic journals to read. They can range from introductory to advanced, as long as it's free (requires no access fees). Feel free to edit this question ...
97 views

### Efficiency of chaining AES “groups” of blocks

From ISO/IEC 23001-7:2012/Amd 1:2012 10.2.2 Creation of Initialization Vector (Informative) Decryption efficiency may be improved if subsequent initialization vectors use the value of the last ...