instruction stringlengths 15 30k |
|---|
Is use of pre-shared key for sharing session key in symmetric key cryptography vulnerable to MITM? |
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 supported by several libraries and with fast implementations in hardware, and on its own GCM has nice properties including ... |
Consider the following protocol:
Alice ------------------------> R1 Bob
Alice k(R1),R2 <----------------------- Bob
Alice ------------------------> k(R2) Bob
Alice k(S) <------------------------ Bob
Where
- `k... |
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?
In my scheme there would be a server getting the votes and the server shouldn't see who voted what. However we can co... |
A general theoretical answer to the title's _What makes LSBit stenography detectable?_ is that in normal images, the LSBit of a pixel in some channel is correlated to higher-order bits in the same pixel and channel, that pixel in other channels, and adjacent pixels, in ways that mere replacement of LSBit tends to stron... |
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 ?
1. AES-ECB($key$ , $msg$)
2. SIV($key$, NIL , $msg$) where associated data is NIL.
I could not make out much from Rogaway , Shrimpton's paper on "Determi... |
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 ?
1. AES-ECB($key$ , $msg$)
2. SIV($key$, NIL , $msg$) where associated data is NIL.
I could not make out much from Rogaway , Shrimpton's paper on "Determi... |
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][1], we can gain a speed boost in private-key operation, with little (conjectured) reduction in security for small-enough $k$; the speedup factor relative to 2-pr... |
I would like to ask what happens if we build an RSA system with modulus a product of more than 2 primes, for example let $n=p_{1}p_{2}...p_{L}$. I know only the classical RSA system with $n=pq$ with $p$ and $q$ large prime numbers.
I guess the modulus $n=p_{1}p_{2}...p_{L}$ will be not a good idea, because one can us... |
A general theoretical answer to the title's _What makes LSBit stenography detectable?_ is that in normal images, the LSBit of a pixel in some channel is correlated to higher-order bits in the same pixel and channel, that pixel in other channels, and adjacent pixels, in ways that mere replacement of LSBit tends to stron... |
Currently busying myself with the Bitcoin "mining" algorithm, I am wondering if the process really cannot be simplified.
For reference, the algorithm is basically SHA-256d:
$success := SHA256( SHA256( IV || nonce ) ) < target$
The resulting hash of 256 bits is then interpreted as a single number of 256 digits ... |
SHA-256: (Probabilistic?) partial preimage possible? |
It is known, for example, that exposing 50% of most siginificant bits of RSA private exponent *does not provide security risk*. So how to qualify *security degradation* of partial exposure of *plaintext* in RSA encryption? Can we say, for example, that exposing 50% of plaintext does not reduce security? And, is there l... |
How much plainext could be known without reducting security of RSA? |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. This standard supports a public key $(n,e)$ where the modulus $n$ is the product of $u≥2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). The private exponent $d$ is such that $1<d<n$, and $e⋅d≡1\pm... |
It is known, for example, that exposing 50% of most siginificant bits of RSA private exponent *does not provide security risk* (when a small public exponent it used). So how to qualify *security degradation* of partial exposure of *plaintext* in RSA encryption? Can we say, for example, that exposing 50% of plaintext do... |
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 degradation* of partial exposure of *plaintext* in RSA encryption? Can we say, for example, that exposing 50% of plaintext doe... |
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 32.
While that does sound like a nice salt, I am a bit doubtful of the 1000-iteration idea. While this does make bru... |
I am currently implementing Shamir's ID Based signature scheme as defined in the [original paper](http://islab.iecs.fcu.edu.tw/GroupMeeting/PowerPoint/g20050422_1.pdf). The sign and verify operation are defined as follows:
Sign: $s = g * r^{f(t,m)} (\mod n)$
Verification: $s^e = i * t^{f(t, m)} (\mod n)$
I hav... |
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 be interested in a way that from one password word would generate a given number, for example 7, permutations for use ... |
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 be interested in a way that from one password word would generate a given number, for example 7, permutations for use ... |
The [OTP][1] 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 [S/KEY][2] standard. Are there any?
[1]: http://en.wikipedia.org/wiki/One-time_password
[2]: http://en.wikipedia.org/wiki/S/K... |
The One-Time-Password ([OTP][1]) 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 [S/KEY][2] standard. Are there any?
[1]: http://en.wikipedia.org/wiki/One-time_password
[2]: http://en.wi... |
A general theoretical answer to the title's _What makes LSBit steganography detectable?_ is that in normal images, the LSBit of a pixel in some channel is correlated to higher-order bits in the same pixel and channel, that pixel in other channels, and adjacent pixels, in ways that mere replacement of LSBit tends to str... |
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 encryption.
Is my stenography easy to detect? And what would it take to conceal it? |
What makes LSBit steganography detectable?And what would help in concealing it? |
What makes LSBit steganography detectable? And what would help in concealing it? |
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 *known* techniques - using known algorithms and hardware.
**But, from a meta-cryptographic point of view, how do we just... |
What informal indicators exist for estimating the computational infeasibility of cryptographic problems? |
The question
====
There are limits to how much you can use a the DRBG before you have to reseed
it. But are there limits to much you must use it before reseeding? Take the
following scenarios as an example.
Usually you seed the DRBG once, then you use that instance until you reach the
reseed limit. Like so:... |
Seed / reseed DRBG too often? |
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 *known* techniques - using known algorithms and hardware.
**But, from a meta-cryptographic point of view, how do we just... |
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 *known* techniques - using known algorithms and hardware.
**But, from a meta-cryptographic point of view, how do we just... |
There is OpenBSD, where you can use S/KEY for login-purposes.
Check the [OpenBSD – Frequently Asked Questions][1]:
> # 8.10 - S/Key
> S/Key is a ``one-time password'' authentication system. It can be useful for people who don't have the ability to use an encrypted channel which protects their authentication cr... |
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…
Usually you seed the DRBG once, then you use that instance until you reach the
reseed limit. Like so:
seed... |
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 rounds of
> the DES block cipher. DES2 has the same block and key size as DES. For
> this question you should consider th... |
Your Formulas are alright, but there is some additional information from the exercise/setup:
The exercise states, that $F$ should be considered as a blackbox (otherwise you could use the internal stages of $F$, as poncho already suggested). However, as I understand it you can stil evaluate $F$ on any input of your c... |
[Lagrange interpolation][1] seems to be affected by the so-called [Runge phenomenon][2] when one tries to interpolate polynomials of high degree from a set of equidistant points.
Lagrange interpolation is used in some secret sharing schemes like [Shamir's secret sharing][3], in which the polynomial being interpolat... |
Does Runge phenomenon affect Shamir's secret sharing scheme? |
I am studying hash functions. I can understand why collision resistance implies second preimage resistance, but I don't get why second preimage resistance should imply first preimage resistance.
Could anybody be help me with this argument from _Introduction to Modern Cryptography_ by Katz & Lindell, please?
> 1. ... |
I haven't seen the Shamir ID-based signature algorithm, but I think you want to use .powMod(exponent, modulus), and not, for performance and/or OutOfMemory reasons, .pow(exponent).mod(modulus). E.g. for forming the signature
<code><br />
BigInteger g=???;<br />
BigInteger r=???;<br />
BigInteger ftm=???;<br />
Big... |
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 known weaknesses of a scheme like this which aims to provide confidentiality and integrity? The hash could also be an HMA... |
Compared to GCM or XTS modes, how secure is H xor R1, E (R2, R1, Message) for confidentiality and integrity? |
I don't see any reason to expect this to provide integrity (INT-PTXT or INT-CTXT). In fact, if $R1,R2$ were known to the attacker, I can show that in general it does not provide integrity: there exist some encryption algorithms that are IND-CPA secure but where your scheme does not provide integrity. (e.g., any strea... |
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 queue would make it decently pseudorandom.<p>
Has there been studies on script execution time as a source of pseurandom... |
Is script execution time a decent source of pseudorandom number generation? |
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 questions about design of the encryption system and not about its usage.
How is LUKS dm-crypt secure if the key is store... |
How is LUKS dm-crypt secure if the key is stored with the encrypted data? |
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 decryption key (and possible other parameters).
But we always talk about digital encryption, never anything that would ... |
Why not use Fermat's Little Theorem to calculate your inverse instead?
ie a^{phi(m)-1}=a^-1 mod m
Although this would require repeated squaring (which is also vulnerable to side channel attacks) the number you would obtain from any attack would be the exponent, not the thing you were calculating the inverse of... |
Why not use Fermat's Little Theorem to calculate your inverse instead?
ie
$$a^{phi(m)-1}=a^{-1}\mod{m}$$
Although this would require repeated squaring (which is also vulnerable to side channel attacks) the number you would obtain from any attack would be the exponent, not the thing you were calculating the... |
The following was originally written as an edit to the question, but I'm going to put it here instead because I think formalizing the schemes might well provide you with enough of a hint for you to solve this question yourself...
---------------
Let $f(k,m)$ be a pseudo-random function, taking as inputs a key and... |
How do I prove the following MACs are insecure?
http://i273.photobucket.com/albums/jj204/TippIiez_Cassiopeia/MAC1_zps49f906ae.jpg
http://i273.photobucket.com/albums/jj204/TippIiez_Cassiopeia/MAC2_zps10578f55.jpg |
How do I prove the following MACs are insecure?
<img src="https://i.stack.imgur.com/E355y.jpg" width="300">
<img src="https://i.stack.imgur.com/gHyaD.jpg" width="300">
1
2 |
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 implement? In either mode, I will use the disk sector # to provide randomness to ensure that 2 sectors of same data will e... |
Why do we use XTS over CTR for disk encryption? |
The following was originally written as an edit to the question, but I'm going to put it here instead because I think formalizing the schemes might well provide you with enough of a hint for you to solve this question yourself...
---------------
Let $f(k,m)$ be a pseudo-random function, taking as inputs a key and... |
The following was originally written as an edit to the question, but I'm going to put it here instead because I think formalizing the schemes might well provide you with enough of a hint for you to solve this question yourself:
---------------
Let $f(k,m)$ be a pseudo-random function, taking as inputs a key and a... |
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 or a work order. I just want to go to the next level from “supply a proper RNG”.
A proper RNG should be built on a cr... |
I know I am in delay, but just to give my opinion:
AES may be secure, even RSA may be secure but unlike the one time pad they do not have a mathematical proof of being secure. And the fact that NSA recommends to use AES give me some doubts…
- Do they recommend this because they know how to break it?
- Why did th... |
I'm assuming Bob uses the standard format, [OpenPGP][1] aka [RFC4880][2], to store his private key in a private keyfile.
If the adversary Eve somehow obtains Bob's private keyfile, and the passphrase on that keyfile is so short and weak that the adversary breaks it with a dictionary attack or brute force, then -- Th... |
I wonder if there are arithmetic functions that simulate PRPs and PRFs ? Generally we use block cipher ? is there another solutions ?
Thank you.
|
How do you perform the Burmester-Desmedt key exchange Protocol, in Diffie-Hellmann
extension protocol ?
I've been searching high and low, but couldn't locate an example on how to prove if all the party is getting the same session key.
Here is the explanation that i get from net:
![enter image description here]... |
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 is getting the same session key.
Here is the explanation that I got from the net:
. 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 ensures that every byte is being compared rather than a simple string compari... |
Despite the fact that Marsaglia's MWC PRNG (multiply-with-carry random number generator) is considered to be *"the mother of all RNGs"*, it does not seem to be considered to be a CSPRNG (cryptographically secure pseudo-random number generator) even though it passes several statistical randomness tests, including *ENT* ... |
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 explained?
Can one generate an algorithm combining the public key and private key of RSA algorithm to make it a symmetric ke... |
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 words, how secure was a message encrypted with the best available methods from the attackers of its day, up t... |
How has the "power" of cryptography evolved from its beginnings till today? |
Germany's BSI has produced [AIS 31][ais31] that includes requirements on Physical True RNGs (PTRNGs). It is designed to fill a gap in the Common Criteria standard.
> Chapter 4 describes pre-defined classes for physical true, non-physical true, deterministic and hybrid random number generators. ... The basic concepts... |
As far as I know, there are three standard options for the three keys $K_1$, $K_2$ and $K_3$ used by 3DES:
1. Three distinct keys.
2. The first and last key are equal: $K_1$ = $K_3$.
3. Three equal keys: $K_1 = K_2 = K_3$
I wonder whether there is a way to find out which one of these options is (most likely)... |
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:
1. Three distinct keys.
2. The first and last key are equal: $K_1$ = $K_3$.
3. Three equal keys: $K_1 = K_2 = K_3$
I wonder whether there is a way to find out which one of these options is (most likely)... |
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 construction of a subset of BN curves where it easy to find the sextic twist. For instance, one knows through the contructi... |
Sextic twist optimization of BN pairing - cubic root extraction required? |
I would have made this a comment, but I don't have enough reputation points.
I think this is a good question. I don't see how a timing attack could be done in any practical manner. I ran a quick test on two 256 bit/32byte keys I generated. I did a simple "for" over them, comparing each character. Only the last b... |
Is there any function $f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$ and this function invertible (easy to find $x \in \mathbb{Z}_n$ such that $f(x) \in \mathbb{Z}^\times_n$ ) ?? |
$f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$? |
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 with many rounds (taking 500ms on my Intel i5-3570).
I want to use the keychain (like available in Mac OS or some other ... |
Storing password or derived key in keychain? |
Firstly, $|\mathbb Z_n|=n$, whereas $|\mathbb Z_n^*|=\varphi(n)<n$. So, by the [pigeon-hole principal](http://en.wikipedia.org/wiki/Pigeonhole_principle) there cannot be a mathematically invertible function
$f:\mathbb Z_n\to\mathbb Z_n^*$.
So, lets relax our idea of what 'invertible' means a bit. How about ensuring... |
Firstly, $|\mathbb Z_n|=n$, whereas $|\mathbb Z_n^*|=\varphi(n)<n$. So, by the [pigeon-hole principal](http://en.wikipedia.org/wiki/Pigeonhole_principle) there cannot be a mathematically invertible function
$f:\mathbb Z_n\to\mathbb Z_n^*$.
So, lets relax our idea of what 'invertible' means a bit. How about ensuring... |
Firstly, $|\mathbb Z_n|=n$, whereas $|\mathbb Z_n^*|=\varphi(n)<n$. So, by the [pigeon-hole principal](http://en.wikipedia.org/wiki/Pigeonhole_principle) there cannot be a mathematically invertible function
$f:\mathbb Z_n\to\mathbb Z_n^*$.
So, lets relax our idea of what 'invertible' means a bit. How about ensuring... |
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 $x \in \mathbb{Z}_n$ such that $f(x)=y$. |
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 with many rounds (taking 500ms on my Intel i5-3570).
I want to use the keychain (like available in Mac OS or some other ... |
I would have made this a comment, but I don't have enough reputation points.
I think this is a good question. I don't see how a timing attack could be done in any practical manner. I ran a quick test on two 256 bit/32byte keys I generated. I did a simple "for" over them, comparing each character. Here are the re... |
I been going through some cryptography exercises and stumbled across this problem.
> Discover message $m$. You know that $m = p * q$. Also $p ^ 5 mod N$,
> $q ^ 5 mod N$ and $N$ are known numbers.
I am really lost and don't know where to start. Could anyone give some hints or point me to right direction wher... |
I would have made this a comment, but I don't have enough reputation points.
I think this is a good question. I don't see how a timing attack could be done in any practical manner. I ran a quick test on two 256 bit/32byte keys I generated. I did a simple "for" over them, comparing each character. Here are the re... |
I would have made this a comment, but I don't have enough reputation points.
I think this is a good question. I don't see how a timing attack could be done in any practical manner. I ran a quick test on two 256 bit/32byte keys I generated. I did a simple "for" over them, comparing each character. Here are the re... |
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 construction of a subset of BN curves where it easy to find the sextic twist. For instance, one knows through the contructi... |
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 any detail beyond that is beyond me.
Is ed25519 a hash signature with respect to the tag? If so, is it believed ... |
It is not clear if you simply saw that tag somewhere or if someone tagged an ed25519 related question with this tag?
But ed25519 or more general the [EdDSA](http://en.wikipedia.org/wiki/EdDSA) (Edwards-curve Digital Signature Algorithm) approach can be considered as a variant of [ElGamal signatures](http://en.wikip... |
Writing [my last question](http://crypto.stackexchange.com/q/14676/12164), I saw the [tag: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 any detail beyond that is beyond me.
Is ed25519 a hash signa... |
This question is inspired by this [recent one][1]. I worded it as homework that could be asked in a _computer security with applied cryptography_ class.
Some system keeps track of user passwords as `(userID, H)` pairs with `H` of 20 octets and a single pair per `userID`. To test an alleged `Password` for some `userI... |
This question is inspired by this [recent one][1]. I worded it as homework that could be asked in a _computer security with applied cryptography_ class.
Some system keeps track of user passwords as `(userID, H)` pairs with `H` of 20 octets and a single pair per `userID`. To test an alleged `Password` for some `userI... |
This question is inspired by this [recent one][1]. I worded it as homework that could be asked in a _computer security with applied cryptography_ class.
Some system keeps track of user passwords as `(userID, H)` pairs with `H` of 20 octets and a single pair per `userID`. To test an alleged `Password` for some `userI... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.