2
votes
2answers
519 views

Using ECDSA keys for encryption

I know that ECDSA is used for signature only, but I wonder if I can use the public/private Elliptic Curve keys for encryption too. I have ECDSA SSH public keys and I wonder if I can use them to ...
2
votes
1answer
215 views

Find out which keying option is being used in Triple DES?

As far as I know, there are three standard options for the three keys $K_1$, $K_2$ and $K_3$ used by 3DES: Three distinct keys. The first and last key are equal: $K_1$ = $K_3$. Three equal keys: ...
4
votes
0answers
72 views

How has the “power” of cryptography evolved from its beginnings till today? [closed]

I'm looking for a historical overview for the change in cryptographic power, which I hereby define as How far state-of-the-art cryptography is ahead of state-of-the-art cryptanalysis. In other ...
1
vote
2answers
235 views

Digital Signature using symmetric key cryptography

Generally digital signature is a public key cryptography concept.But it needs high overhead. So is there any publication or link available where 'digital signature using symmetric key' has been ...
1
vote
2answers
191 views

pbkdf2 password validation

My question is related to PBKDF2. I am unsure how to validate user entered password with already existing hashes and salts. I have heard of the so called "length-constant" comparison which basically ...
1
vote
1answer
262 views

AES CBC Security

I am building an Apache webserver with TLS 1.2 and OpenSSL 1.0.1. So far, I have enabled 2 encryption algorithms - ECDHE AES256 GCM and ECHDE AES128 GCM. Firefox and Chrome(ium) use NSS which ...
4
votes
1answer
200 views

Timing Attack on RSA

So far I have researched on timing attack on RSA, We all know the ransomware named Cryptolocker it uses RSA 2048 bit encryption. Now is it possible to break the encryption using timing attack. I have ...
1
vote
1answer
199 views

Burmester-Desmedt (BD) key agreement protocols

How do you perform the Burmester-Desmedt key exchange Protocol, in Diffie-Hellman extension protocol? I've been searching high and low, but couldn't locate an example on how to prove if all the party ...
2
votes
2answers
192 views

PRP, PRF and modular arithmetic

Are there any arithmetic or mathematical functions that can be used as PRPs or PRFs ? Since, Conventional block ciphers like AES are that are proven to be good PRPs are not based on mathematics but ...
1
vote
2answers
113 views

Standard or guidance for entropy collection

I need to write some high-level security requirements which include a random number generator suitable for use in cryptography. I don't need something very formal, this isn't a security certification ...
9
votes
2answers
446 views

Why do we use XTS over CTR for disk encryption?

I'm taking Prof. Boneh's crypto class from Coursera, and am unsure on the requirement for XTS mode for disk encryption. It seems that CTR mode would do exactly what XTS can do, but is simpler to ...
1
vote
1answer
85 views

Prove that two MACs with incremendal PRF application are not secure

How do I prove the following MACs are insecure?                                                        1                                                                                   2
2
votes
1answer
222 views

How is LUKS dm-crypt secure if the key is stored with the encrypted data?

I've posted this question over at superuser, but haven't had any success at getting answers. That's why I've posted it here. Furthermore, I believe this is a more appropriate place for it as it is ...
1
vote
1answer
84 views

Is script execution time a decent source of pseudorandom number generation?

This is for a PHP script for password generation. Naturally there are other things being calculated before the password is generated. But I figure the time it takes for the script to initialize and ...
1
vote
1answer
134 views

Compared to GCM or XTS modes, how secure is H xor R1, E (R2, R1, Message) for confidentiality and integrity?

Let R1 and R2 be (32 byte) random values, and let a H = Hash (R1, R2, Message) be of the same length as each R value. Provided E (R2, R1, Message) is operating in some chaining mode, are there any ...
3
votes
1answer
132 views

Does Runge phenomenon affect Shamir's secret sharing scheme?

Lagrange interpolation seems to be affected by the so-called Runge phenomenon when one tries to interpolate polynomials of high degree from a set of equidistant points. Lagrange interpolation is ...
2
votes
2answers
182 views

Seed / reseed DRBG too often?

There are limits to how much you can use a the DRBG before you have to reseed it, but are there any limits to how much you must use it before reseeding? Take the following scenarios as an example… ...
3
votes
0answers
69 views

What informal indicators exist for estimating the computational infeasibility of cryptographic problems?

When assuming a block cipher primitive is secure, or a number theoretic problem is hard, this assumption is usually based on how far we are from breaking the primitive or solving the problem using ...
2
votes
1answer
64 views

Practical usage of S/KEY

The One-Time-Password (OTP) topic became quite popular in the recent years. But unlike the well-known HOTP and TOTP standards I haven't heard about any applications/systems implementing and using the ...
5
votes
3answers
244 views

Get permutations from password

Are there any "good" ways to get a permutation from a password/pass-phrase? If one, for example, wanted to get a permutation of letters from a password, how might one do that in a smart way? I would ...
5
votes
2answers
559 views

Analogue encryption algorithms

I have a basic understanding of how strong encryption works on digital data. Bits can be changed so that they appear completely random and map one-to-one back to the original set, given the correct ...
1
vote
2answers
73 views

Shamir's ID based signatures - Notation issues

I am currently implementing Shamir's ID Based signature scheme as defined in the original paper. The sign and verify operation are defined as follows: Sign: $s = g * r^{f(t,m)} (\mod n)$ ...
3
votes
2answers
227 views

Hashing SHA-512 1000 times

SageMathCloud security (http://goo.gl/dCujW1) is as follows: Only the hash of your password is stored by the server, which uses 1000 iterations of the sha-512 hash function, with a salt length of ...
3
votes
0answers
101 views

How much plainext could be known without reducting security of RSA?

It is known, for example, that exposing 50% of most significant bits of RSA private exponent does not provide security risk (when a small public exponent it used). So how to qualify security ...
1
vote
0answers
72 views

Which gives better deterministic encryption SIV or Plain ECB mode?

Lets say , if we encrypt a plain text message $msg$ with key $key$ in below two ways. Which is the below would give better deterministic encryption and why ? AES-ECB($key$ , $msg$) SIV($key$, NIL , ...
2
votes
5answers
150 views
1
vote
1answer
70 views

Necessity of changing $p$ and $q$ when your private key is exposed?

Suppose your private key $d_1$ has been exposed. Instead of changing $p$ and $q$, instead you just choose a new public and private key (say $e_2$ and $d_2$) and use these instead. What kinds of ...
1
vote
1answer
95 views

Homomorphic crypto allowing anonymous yes/no votes?

I'd need a crypto system allowing online yes/no votes but without revealing who voted what. Is a "partial" homomorphic crypto system what I'm after? Would, for example, Damgard-Jurik work in my case? ...
2
votes
1answer
137 views

Is it possible to tweak AES-GCM so that it is satisfactory for whole-disk encryption (like XTS mode)?

Is it possible to leverage a preexisting implementation of AES-GCM to provide the key security benefits essential for full-disk encryption (similar to AES-XTS)? GCM is a popular encryption mode ...
1
vote
0answers
115 views

How does converting character set affect hash entropy?

Does mapping a large character-set hash onto a small character-set hash lower entropy for a fixed size substring? I'm writing a python app that involves generating passwords for websites. During the ...
1
vote
1answer
100 views

What makes LSBit steganography detectable? And what would help in concealing it?

In a project of mine I took a 24-bit bitmap image and I performed LSBit steganography over it (saved a black and white image inside each of the planes R, G, B) using pixel shuffling and xor ...
2
votes
1answer
93 views

Secrete message sharing using N private keys

I'm looking for an encryption scheme that could possibly meet the following requirements. Let, $X = plaintext$ $M = (pub, priv)$, where $priv == (Ky + Kz)$ Given ...
1
vote
1answer
131 views

Non-interactive Zero-knowledge proof signature validation without public key

I'm looking for a method for a scenario with following requirements: At least 3 people (A,B,C,...) are in a Network where they can broadcast messages to everyone but not communicate with a specific ...
1
vote
1answer
201 views

Exercise: Attack on a Two-Round DES Cipher

Working through the exercises in Cryptography Engineering (Schneier, Ferguson & Kohno) I have stalled on the following exercise: Consider a new block cipher, DES2, that consists only of two ...
-2
votes
1answer
34 views

Finding if exponent share is present in dlog instance [closed]

Let $g$ be a group generator of prime order $q$. Suppose we are given two elements $g^y$ and $x_1$. Can we find out if $y=x_1+x_2$ for some $x_2$? Thanks
0
votes
1answer
119 views

Digital signatures under plain RSA

Show that digital signatures under plain RSA are insecure (Plain RSA means that signing is done by calculating $m^d\bmod n$, with $0\le m<n$, and no padding or hashing of $m$). Write an algorithm ...
2
votes
1answer
159 views

Is it necessary to use single hash function for signature generation and HMAC?

I am trying to figure out if we need to use single hash function across all the places in a ssh session. i.e – signature generation/verification and HMAC calculation/validation. Is it possible to use ...
0
votes
1answer
133 views

Partially-known-plaintext attack of a stream cipher based on modular arithmetic

I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ ...
9
votes
0answers
300 views

Who first published the interest of more than two prime factors in RSA?

Multi-prime RSA is now a well known technique: it uses $k>2$ distinct secret prime factors in the public RSA modulus, with the advantage that, using the CRT, we can gain a speed boost in ...
4
votes
2answers
220 views

Block Ciphers and (Non-)Generic Attacks

I am currently reading through Cryptography Engineering and came across this definition of block cipher security: Definition 2 An attack on a block cipher is a non-generic method of ...
0
votes
2answers
138 views

IV/Nonce in CTR&GCM mode of operation

We know reusing IV can compromise our secrecy. I have some questions aiming to clarify the use of an IV/Nonce in CTR/GCM: Is it OK to use the same key for encrypting plain-texts in authenticated ...
0
votes
0answers
46 views

Private Set Intersection Polynomial Computation [duplicate]

I am trying to implement the protocol mentioned in Section 3.4 of “Efficient Robust Private Set Intersection” in Java. In the Second Step, the Client computes a polynomial of degree $n$ over the ...
2
votes
1answer
86 views

Proving that a function is not a OWF (One-way-function)

I was trying to prove that a given function is not a one way function and I was not sure how to do it because maybe I had unclear what a one way function was (OWF). The definition that I have for a ...
1
vote
1answer
106 views

Simplified Fiat-Shamir example generates wrong output

I am trying to implement the Fiat-Shamir identification protocol, however the end results always fail to match. I am using algorithm's description from here. Preparation: Select 2 prime integers ...
1
vote
1answer
97 views

Is there a method to combine encryption and ring signing?

There's the well-known question on whether to sign or encrypt first. However, if instead a message is to be ring-signed such that either recipient could be the actual signer, is there any scheme that ...
1
vote
1answer
81 views

Does a cofactor of an elliptic curve have to be an integer?

What are the implications of a curve having a non-integer co-factor for its generator point? Is that even possible?
0
votes
2answers
360 views

My SSH server public key is 2048 bits, but my account's private key is 4096. What is my effective security?

My SSH server has a 2048-bit public key. But my private key, for clients to login, is 4096-bit. In this case, do I have the brute force protection of 2048 or 4096 bits? My worry is that someone ...
3
votes
2answers
206 views

GCM encryption for 256-bit and 512-bit block ciphers

The Galois/Counter Mode of Operation (GCM) This paper describe using GCM mode with 128-bit and 64-bit block cipher. Can we use this mode for 256-bit and 512-bit block cipher?
3
votes
2answers
149 views

Do deterministic secret sharing schemes exist?

Are there algorithms for secure secret sharing such that the algorithm depends solely on the value being secured, relying on no randomness in its calculations. If there aren't, is such an algorithm ...
1
vote
1answer
118 views

Hash functions with or without secret key

The classical definition of hash functions (found in books) are OK, but when studying a little more there is a lot of notions that seem ambiguous (contradictory) to me : Sometimes we have hash ...

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