All Questions

23 views

change in bits leads to change in rounds the reason? [duplicate]

In AES algorithm why there are 10 rounds for 128 bits whats the reason behind it like we have in raid storage technology or something else
104 views

Making both the IV and salt public for PBE with AES-CFB

Is it okay to make both the IV for AES-CFB and the salt for PBKDF2 public? Does this action of mine compromise security in any way? I have an implementation of this cipher and had previously asked a ...
23 views

Key equal to IV [duplicate]

If I will use for AES encryption in CBC mode key that is equal to IV, how this change security (IV will be secret)?
69 views

Why does NaCl's crypto_auth have twice the security level of crypto_onetimeauth?

The crypto_auth function produces a 256-bit HMAC, with a 512-bit version also available. But the crypto_onetimeauth function ...
167 views

When/why is RSA (hybrid) encryption used rather than alternatives?

I've read that RSA is not meant for encrypting large plaintext because: (Are these also true for other public-key encryptions like ElGamal?) It is slow. Padding makes the ciphertext blocks much ...
108 views

Is super encryption (aka “multiple encryption”) always good?

I'm trying to use super encryption (also known as “multiple encryption”) with AES in CFB mode with IV and password salting and AES in CTR mode both without padding. I first use AES CFB and then AES in ...
679 views

Which bitwise operations are used in SHA-256?

From the wikipedia entry on SHA-256 I'm a bit confused about which operations actually go into the algorithm. From the pseudo code it appears the operations are $\texttt{xor}$, $\texttt{and}$, rotate, ...
1k views

RSA & DH at risk due to math advances, will this eventually affect elliptic curves too?

I was looking into the predictions by some researchers that RSA and Diffie-Hellman may not be secure in the next few years due to advances in math and being able to calculate the discrete logarithm ...
145 views

Is there any alternative for extended euclidean algorithm to perform modulo division?

I'm implementing point addition and point doubling operations for elliptic curve cryptography. I have implemented extended euclidean algorithm to perform modulo division. It appears the that ...
236 views

Modular exponentiation on calculator for textbook RSA

How do you encrypt $51$ with public key $(n,e) = (91,23)$ I understand that $c = 51^{23} \bmod 91$. How can I calculate the result on a calculator?
31 views

Is EFS vulnerable to Chosen plaintext attack?

I have some backed up files encrypted with EFS and I lost the EFS certificate thus unable to decrypt the files. I understand that EFS uses the user certificate public key to encrypt the symmetric key ...
762 views

Exchanging encrypted messages, and decrypting without a public key?

I know very little about encryption, but I was hoping someone could shed light on this cipher text exchange scheme I worked out in my head this morning: Bob wants to send Alice a message but doesn't ...
292 views

Cracking plain RSA by factoring the modulus n

This is the setup: I have both public and private keys of one "instance" of RSA. And I have only the public key of another RSA cryptosystem, but this system has the same modulus as the first one. I ...
23 views

Why do we need Merkle–Damgård strengthening [duplicate]

Reading through some manuals, wikis and other documentation I'm learning about Merkle–Damgård construction. I understand why padding beginning with '1', followed by '0's is needed, but I can't ...
210 views

Do I understand (below) why Q = dP is easy while finding d is hard

As we all know for discussion of Dual_EC_DBRG, the point on an elliptic curve Q can be calculated from P and some (large) integer d $Q = dP$ And we know that knowledge of Q and P is not sufficient ...
49 views

How secure is 'Plain Old RSA' [duplicate]

Let's say I use RSA encryption, it's 2048 bits and I use a simple character padding scheme, every character is turned into a 3 digit number and strung together, then encrypted. Saying that no message ...
909 views

Two different keys decrypting same content

is there some generally available algorithm which will encrypt a short string and generate two unique keys so that any of the two can be used to decrypt the message again? It doesn't has to be "super ...
16k views

How can I use asymmetric encryption, such as RSA, to encrypt an arbitrary length of plaintext?

RSA is not designed to be used on long blocks of plaintext like a block cipher, but I need to use it to send a large (encrypted) message. How can I do this?
72 views

Schnorr Ring Signatures - wrong hash results

I don't know if I've placed the question right, It is half maths, half programming. I'm writing Schnorr Ring Signatures on Elliptic Curves in Java and I have a problem. I've found scheme on integers ...
62 views

Information theoretical security of an inefficient Shamir based access structure

I have studied Sharmir's scheme as well as the multiple assignment scheme proposed by M. Ito. My question is if anyone can tell me if the following scheme is theoretically secure: Terms: P = set of ...
52 views

What happens if you multiply a point with its order on complete Edwards curves?

I was recently working with some ECC crypto and stumbled across the following phrase on the SafeCurves page: The rational points of a complete Edwards curve are the pairs (x,y) of elements of ...
116 views

How long can a RSA public key be?

If I create an RSA of 4096 bits, what would be the range of the length in bytes of the public key in DER format? Also, will the private key always be exactly 4096 bits (512 bytes)? Does the public ...
107 views

Password in first line of file for AES-256 encryption

I'm using openssl with aes-256-cbc encryption to encrypt a file. The password is on the first line of the file and the ...
185 views

RSA Attack, known public key and ciphertext. Can decrypt the message m?

I'm stuck with this problem: Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key $(217,7)$, Alice send the ciphertext $c=53$ to Bob through RSA encryption. Now, Eve ...
89 views

Comparison Vigènere vs. Monoalphabetic cipher

I have a question for a class of secure communication, but I have no idea about how to proceed in order to answer it. I'll be very grateful to whom replies to me. Assuming that brute force attack ...
3k views

What are SNARKs?

What does it mean and what is it used for, I have been hearing this term a lot lately. From the context I've heard it talked about it seems to be connected with zero knowledge?
7k views

Is secp256r1 more secure than secp256k1?

Curves secp256r1 and secp256k1 are both examples of two elliptic curves used in various asymmetric cryptography. Googling for these shows most of the top results are Bitcoin related. I've heard the ...
2k views

Prevent double-spending with decentralized digital currencies without all transactions being public?

A recent approach to creating a decentralized online currency, called Bitcoin, has been generating some interest. The goal is to have a way to transfer currency without a central authority and without ...
67 views

What algorithm to use to rotate values in a predefined manner and be able to decrypt them back to the original?

What is the best practice to accomplish this? For example, let's have an initial value abc123456 and a seed secret_hash. I want ...
171 views

How should I generate secure random numbers deterministically?

I have a 256-bit seed; call it P. From P, I need to derive 219 256-bit numbers deterministically. There's a catch, however: I want to derive them in any order. For example, I might need the 7878th ...
4k views

Why can't I reverse a hash to a possible input?

I'm going to provide “proof” why a hash function can be reversed, and I hope you can tell my why I'm wrong So, a hash function can be implemented as a series of logic gates. All logic gates can be ...
212 views

Memory-hard proof-of-work: are they ASIC-resistant?

Is a memory-hard proof-of-work scheme necessarily resistant to speedups from custom ASICS? Background: Bitcoin uses a proof-of-work scheme based on SHA256 hashing. The scheme is compute-bound. ...
64 views

Encrypt the network adapter mac address so i can get 20 or 25 cipher text length

How do I encrypt a 12 character network adapter mac address so i can get in result with a 20 to 25 cipher text length?
401 views

How can I do minus on plaintexts in the Paillier cryptosystem?

We have $E(a)$, $E(b)$ encrypted under the same Paillier key. As we all know, we can get $E(a+b)$ by calculating $E(a)*E(b)$. But can we get $E(a-b)$, by calculating $E(a)/E(b)$? I tried to ...
30 views

Checking for factor base

In algorithms like Dixon's factorization a factor base is used, which contains all primes below a bound. Then calculates $x^2 \mod n$, and then checks it is in factor base or not. Suppose $P$ is ...
238 views

What is the most secure ECC Curve?

I have for a while used Koblitz curve (sect571k1), in ECDH and ECDSA. But I have started wonder if it is the most secure. I prefer security over efficiency. So the curve doesn't have to be the most ...
98 views

I'm using this kind of technique instead of padding of cipher buffer (here goes pseudo-code): ...
88 views

All the affine points on the curve

I have calculated the affine points on the curve $x^2 + y^2 = 1 − 3x^2y^2$ over the field ${\mathbb{Z}}_{11}.$ Using $y^2 = \frac{1-x^2}{1+3x^2}$ I got the following points: ...
135 views

What is the best current way to cryptographically secure databases?

I'm currently working on a proposal for some secure complete system and one of the things currently lacking is the database security. However I don't want to roll my own crypto there and thereby need ...
56 views

Problem with this authentication protocol

Consider such authentication protocol: Alice and Bob share a key. Bob sends alice a nonce. Alice encrypts it with shared key and sends to bob. Now assume Alice was successfully authenticated. ...
242 views

How do I get the equivalent strength of an ECC key?

I know how to calculate the comparable symmetric strength of an RSA modulus: calculate the running time for a field sieve. This is how NIST gives approximate symmetric sizes for asymmetric algos in ...
192 views

Certificate Signature Algorithm differs from Signature Algorithm Negotiated for Connection

With the upcoming sunsetting of SHA-1 by browsers I was checking signature algorithms for sites I visit. I'm using Firefox 43.0.2 on Windows. I noticed something interesting when I visited the site ...
43 views

How to check the integrity of a key received through mail using symmetric encryption?

I would like to provide access to encrypted data through a cloud service provider, using a pay-as-you-go model. This means that we will sometimes need to revoke a user's access to the data. To ...
381 views

Koblitz encoding a message to a point, what is the “associated auxiliary base parameter”?

I am looking at the Koblitz method for encoding a message as an elliptic curve point. The first step given in the paper I'm reading is: "Choose an elliptic curve and its associated auxiliary base ...
260 views

Solving Vignere Encryption

I'm currently trying to crack a cypher that I believe is Vignere Encrypted and I'm currently stuck. I calculated the key length by finding repeated sequences in the cypher and calculating the the ...