2
votes
1answer
202 views

Designing a secure IM protocol

I haven't been programming much lately, so I figured I would make an encrypted instant-messaging program (read: Skype clone) with groups to hone my skills. That's not important though, I can do that. ...
4
votes
1answer
1k views

Questions about OAEP for RSA

I have two questions about OAEP for RSA. How are the number of bits to pad with 0 chosen? For example, if I'm sending a 255 byte message with RSA-2048 I have 8 unused bits (1 byte). Should I split ...
2
votes
1answer
354 views

Non-standard signature security definition conforming ed25519 malleability

According to the paper “High-speed high-security signatures”… Malleability. We also see no relevance of "malleability" to the standard definition of signature security. Aside from the example, ...
1
vote
0answers
97 views

Sextic twist of BN pairing parameters vs security

I've previously asked questions on BN pairing parameters. Here's one more. In the BN construction, one is working in a subgroup of a curve over an extension field $\mathbf{F}_{p^{12}}$ for some ...
2
votes
0answers
135 views

Gallant-Lambert-Vanstone method

I am experimenting with the GLV method but cannot manage to get the right results according to the literature. I managed to find lambda, beta, split $K$ into $k_1$ and $k_2$ etc. for the curve I'm ...
1
vote
0answers
43 views

Retrieve cryptographic key knowing cyphertext and plaintext [duplicate]

I was curious about cryptography so I started to learn about symmetric encryption. From what I understand a symmetric encryption works as follow: PlainText -> (Encrypt)K -> Cipher text -> ...
1
vote
1answer
395 views

What is the forward cipher function of AES-XTS?

We're using OpenSSLs EVP_aes_265_xts encryption on data (with unique, random, IVs for every new message encrypted) - which is working well. But, I've been asked; what is the forward cipher function ...
-3
votes
1answer
128 views

RSA public key security issue

The public key for RSA is $[e,n]$. Since $n = p * q$, are $p$ and $q$ already exposed because it takes no effort to figure out $p$ and $q$ from $n$?
3
votes
1answer
172 views

Detecting steganography in the stream of short messages

I have stream of millions of short n-bit (n<30) messages generated by some random number generator. The source of random number generator is not available to me. I suspect there are messages used ...
2
votes
1answer
358 views

Strange Password Hashing

I know about PBKDF2, bcrypt, scrypt, etc. and while I'm not a crypt professional, I think I understand why are they better than just "hash(pass+salt)". But a colleague of mine surprised me with the ...
2
votes
0answers
166 views

What RC4 key value will completely invert $S$ after initial permutation?

What RC4 key value will completely invert $S$ after the initial permutation, so that $S[0] = 255, S[1] = 254, …, S[254] = 1, S[255] = 0$?
2
votes
0answers
67 views

How to generate initial vectors during DPA attack on stream cipher in real life?

I was trying to understand the procedure of the DPA attack on Stream cipher (like Mickey-128). I learned that, the attacker need to build hypothetical power consumption matrix with different initial ...
1
vote
1answer
162 views

Attacking hashed password by timing attack and other means

This question is inspired by this recent one, which raises a point that need to be made quantitative to be meaningfully discussed. I chose an unusual approach: a new question worded as homework that ...
2
votes
1answer
246 views

Is ed25519 a “hash signature”

Writing my last question, I saw the hash-signature tag. I tried to research it best I could, but I'm simply overwhelmed in this field. I don't think it means to simply hash data before signing, but ...
3
votes
1answer
249 views

Decode message $m = p * q$, where $p ^ 5 \bmod N$, $q ^ 5 \bmod N$ and $N$ are known

I been going through some cryptography exercises and stumbled across this problem. Discover message $m$. You know that $m = p * q$. Also $p ^ 5 \bmod N$, $q ^ 5 \bmod N$ and $N$ are known ...
2
votes
0answers
175 views

Storing password or derived key in keychain?

Currently I am developing an application that stores and reads encrypted data. The data is encrypted with AES and the actual AES key is derived from the users password (and some nonce) with PBKDF2 ...
-1
votes
1answer
78 views

$f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$?

Is there any function $f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$ that is invertible? By invertible, I mean it given $y \in \mathbb{Z}^\times_n$, it should be easy to find $x \in \mathbb{Z}_n$ ...
3
votes
1answer
154 views

Sextic twist optimization of BN pairing - cubic root extraction required?

I found the following paper really interesting: http://www.researchgate.net/publication/220378229_A_family_of_implementation-friendly_BN_elliptic_curves/file/79e4150b3a773beecd.pdf It allows ...
5
votes
3answers
3k 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
597 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
94 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 ...
2
votes
2answers
2k 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
520 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
2k 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 ...
5
votes
1answer
367 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 ...
2
votes
1answer
742 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
263 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
149 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 ...
11
votes
2answers
3k 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
113 views

Prove that two MACs with incremendal PRF application are not secure

How do I prove the following MACs are insecure?                                                        1                                                                                   2
3
votes
1answer
934 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
141 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
208 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 ...
4
votes
1answer
156 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
556 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… ...
4
votes
0answers
102 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
157 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
4answers
345 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
3answers
3k 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
94 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
670 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
115 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 ...
3
votes
1answer
242 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
337 views
1
vote
1answer
78 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
171 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? ...
3
votes
2answers
445 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
213 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 ...
3
votes
1answer
162 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
106 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 ...

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