instruction stringlengths 15 30k |
|---|
In continuation to [this][1] question: which else operations are used in symmetric cryptography and why?
What is the difference between addition modulo 2 (xor) and addition modulo 2 ^ register size (addition with overflow)?
[1]: http://crypto.stackexchange.com/questions/8533/why-are-bitwise-rotations-used-in-... |
> 1 - How feasible is it that the chip's manufacturer can predict the output of this PRNG when it passed tests from the people applying the use of this RdRand instruction in kernels?
A strong stream cipher's output is random and unpredictable to anyone __not knowing the key__. See where this is heading? Just because... |
I want to know if having a 8-byte hash value is better than 16-byte hash value for use within hash trees.
My mind tells me that the shorter the hash value, the better. But doesn't a smaller hash value make it easier to invert? More strings would lead to the same hash value.
I guess this is very opinion-based, but... |
I'm currently working with a secure transport protocol that defines the IV to be a counter (incremental nonce) to be encrypted with the same key. This is a followup to a protocol that did not provide any kind of IV.
Could you please describe the possible attack vectors on CBC encryption using this encrypted nonce?
... |
I'm storing the salted hash of a credit card number in a database. What I'd like to be able to do is determine if two different entries in the same database correspond to the same credit card.
Specifically, let $C_1$ and $C_2$ be two credit card numbers (which may or may not be the same). Let $S_1$ and $S_2$ be two ... |
The relationship between recovering the decryption exponent $d$ and factoring the RSA modulus $n=pq$ is a classical question in cryptography. There are three useful answers:
1. The first answer deals with a slightly different question but is useful to gain some insight into the problem. Assume that we given a bit m... |
> How feasible is it that the chip's manufacturer can predict the output of this PRNG when it passed tests from the people applying the use of this RdRand instruction in kernels?
As nightcracker correctly stated, any strong cryptographic PRNG will produce a stream of numbers that pass statistical tests.
However, ... |
The NaCL `ref` implementation of Poly1305 performs modular multiplication to calculate a polynomial $\mod 2^{30} - 5$ using the following modular multiplication function (variables ommitted for brevity):
static void mulmod(unsigned int h[17],const unsigned int r[17])
{
for (i = 0;i < 17;++i) {
... |
How does NaCL Poly1305 implementation do modular multiplication? |
The NaCL `ref` implementation of Poly1305 performs modular multiplication to calculate a polynomial $\mod 2^{30} - 5$ using the following modular multiplication function:
static void mulmod(unsigned int h[17],const unsigned int r[17])
{
unsigned int hr[17];
unsigned int i, j, u;
for... |
The NaCL `ref` implementation of Poly1305 performs modular multiplication to calculate a polynomial $\mod 2^{130} - 5$ using the following modular multiplication function:
static void mulmod(unsigned int h[17],const unsigned int r[17])
{
unsigned int hr[17];
unsigned int i, j, u;
fo... |
How do you prove that a cipher is resistant to differential cryptanalysis? It's said that Rijndael has been proven resistance to differential cryptanalysis. How do cryptographers do that? |
How to prove a cipher resistant to differential cryptanalysis? |
The zerocoin paper mentions such a technique:
> implementers can use the
technique of Sander for generating so-called RSA UFOs
for accumulator parameters without a trapdoor
and refers to:
> T. Sander, “Efficient accumulators without trapdoor extended
abstract,” in Information and Communication Security, vo... |
Are there secure mechanical cryptosystems in use today? Not necessarily alphabetic either, ie digital but mechanical? |
Are there any good examples of Contemporary Mechanical Cryptography? |
Have you heard of the strange story of Dual_EC_DRBG? A random number generator suggested and endorsed by the government that exhibits some very suspicious properties.
http://www.schneier.com/blog/archives/2007/11/the_strange_sto.html
From that article:
"This is how it works: There are a bunch of constants -... |
This is just an idea I had while looking through some threads so take it as you will.
Given a plaintext of any length and a key that a specific hash function is capable of taking as input(I mention this as I know bcrypt has issues with extremely large inputs), what would be the potential issues/attacks of hashing t... |
What prevents continued hashing of a key from being used as a cipher when xored with plaintext? |
This is essentially a (bad) stream cipher. It has multiple problems:
1. You might hit a cycle much sooner than you'd want.
2. It's not parallelizable - this is a large performance issue on modern CPU's compared to algorithms that parallelize well.
3. The key is only inserted at one point of the stream, meaning... |
This is essentially a (bad) stream cipher. It has multiple problems:
1. You might hit a cycle much sooner than you'd want.
2. It's not parallelizable - this is a large performance issue on modern CPU's compared to algorithms that parallelize well.
3. The key is only inserted at one point of the stream, meaning... |
I noticed that non-deterministic primality testing algorithms are more commonly used in practice while there is a deterministic algorithm e.g., AKS which runs in polynomial time? I am right? if so, then why? is there any drawbacks of using AKS?
Thanks, |
Reading some papers on security amplification of weak-PRP written by stefano tessaro, I noticed the use of notion "epsilon-PRP" and the notion of "security amplification". These notions, in conjunction with the statement that "We consequently call a primitive satisfying this assumption an epsilon-PRP: Clearly, AES is m... |
Reading some papers on security amplification of weak-PRP written by Stefano Tessaro, I noticed the use of notion "epsilon-PRP" and the notion of "security amplification". These notions, in conjunction with the statement
> We consequently call a primitive satisfying this assumption an epsilon-PRP: Clearly, AES is mu... |
Reading through some documentation on a piece of software, it claims that a 4-6 digit number is created using a 256-bit encryption process for the purposes of access control. The whole process works as follows:
1. A 4-6 digit "start code" (key?) is chosen by the user and programmed into the client software and into... |
Is it possible to generate a 6-digit number using 256-bit encryption? |
Reading through some documentation on a piece of software, it claims that a 4-6 digit number is created using a 256-bit encryption process for the purposes of access control. The whole process works as follows:
1. A 4-6 digit "start code" (key?) is chosen by the user and programmed into the client software and into... |
As RSA algorithm is use for encryption(plain text to cipher text) and decryption(cipher text to plain text) of data then what is the need of using public key in these sites? where we need to encrypt/decrypt data in Google. how it provide security ? |
why public key cryptography (RSA) is use in sites like Google? |
I believe the claim of using "256-bit encryption" is primarily being done for marketing purposes.
Despite the best efforts of industry experts there are many people with a limited understanding of cryptography, and they associate "bigger key sizes" with "better security." (While this is generally true, it's a very ... |
As RSA algorithm is use for encryption(plain text to cipher text) and decryption(cipher text to plain text) of data then what is the need of using public key in these sites?
why we need to encrypt/decrypt data in Google,how it provide security ? |
How can Alice prove that a message has not been tampered with? |
> 1 - How feasible is it that the chip's manufacturer can predict the output of this PRNG when it passed tests from the people applying the use of this RdRand instruction in kernels?
As nightcracker correctly stated, any strong cryptographic PRNG will produce a stream of numbers that pass statistical tests.
Howev... |
The design documents for Rijndael explain exactly how the designers proved its resistance to differential cryptanalysis.
Read [their submission to the AES competition process](http://csrc.nist.gov/archive/aes/rijndael/Rijndael-ammended.pdf#page=1), particularly Section 8.2 and the Annex. To understand their approac... |
Have you heard of the strange story of Dual_EC_DRBG? A random number generator suggested and endorsed by the government that exhibits some very suspicious properties.
http://www.schneier.com/blog/archives/2007/11/the_strange_sto.html
From that article:
> This is how it works: There are a bunch of constants ... |
> 1 - How feasible is it that the chip's manufacturer can predict the output of this PRNG when it passed tests from the people applying the use of this RdRand instruction in kernels?
As nightcracker correctly stated, any strong cryptographic PRNG will produce a stream of numbers that pass statistical tests.
Howev... |
RSA algorithm is use for encryption(plain text to cipher text) and decryption(cipher text to plain text) of data then what is the need of using public key in these sites,why data is encoded as every thing is viewed by every one?
why we need to encrypt/decrypt data in Google,how it provide security ? |
why public key cryptography (RSA) is use in sites like Google, facebook (what is the need to ecode data in these sites)? |
> 1 - How feasible is it that the chip's manufacturer can predict the output of this PRNG when it passed tests from the people applying the use of this RdRand instruction in kernels?
As nightcracker correctly stated, any strong cryptographic PRNG will produce a stream of numbers that pass statistical tests.
Howev... |
I am assuming there is a very simple way of working this out by brute force, but I am not sure if there is a better way.
I have a file of data that I wish to get (my data, generated by a machine). This file is encrypted by some method that I have no details of (and the company has folded).
However, as well as the e... |
I have two questions here.
1. What does the cipher-text overhead means?
2. Why we were suggested not to encrypts the plain-text itself instead just encrypts only the key (i.e random number) |
What does the cipher-text overhead means? |
1. Cipher Text overhead is the positive difference in length between the encrypted text and the plain text.
- In stream ciphers, the encrypted length is typically equal to the clear text so there is no overhead.
- In block ciphers, there is usually padding involved such that the size of the plain text increases t... |
1. Cipher Text overhead is the positive difference in length between the encrypted text and the plain text.
- In stream ciphers, the encrypted length is typically equal to the clear text so there is no overhead.
- In block ciphers, there is usually padding involved such that the size of the plain text increases t... |
1. Cipher Text overhead is the positive difference in length between the encrypted text and the plain text.
- In stream ciphers, the encrypted length is typically equal to the clear text so there is no overhead.
- In block ciphers, there is usually padding involved such that the size of the plain text increases t... |
I'd like to implement an authenticated key exchange protocol, preferably without rolling my own and with perfect forward secrecy.
I have pre-generated rsa key pairs - each side has the public key of the other side and its own private key, and the goal is to have 256 bits each for cipher (e.g. aes) and hmac key mater... |
What I am trying to do is generate a large (4096bit) random number in JavaScript that is cryptographically safe to use.
My approach is the following:
1. I am creating a `Uint8Array` with the desired length.
2. I am using `Math.random()` to prefill it.
3. I am showing a a 256x256pixel box, and show a message ... |
What I am trying to do is generate a large (4096bit) random number in JavaScript that is cryptographically safe to use.
My approach is the following:
1. I am creating a `Uint8Array` with the desired length.
2. I am using `Math.random()` to prefill it.
3. I am showing a a 256x256pixel box, and show a message ... |
I am reading the birthday attack in [wikipedia][1].
> We consider the following experiment. From a set of $H$ values we
> choose $n$ values uniformly at random thereby allowing repetitions. Let
> $p(n; H)$ be the probability that during this experiment at least one
> value is chosen more than once. This probabil... |
I recently read *Improved Generic Algorithms for 3-Collisions* by Joux and Lucks (Asiacrypt 2009), available as http://eprint.iacr.org/2009/305.pdf. I was wondering about applications of this technique (excluding of course the applications already given in appendix).
So my question is: Are there interesting applicatio... |
I would ask you some questions about users' password storage in a login system.
1. What algorithm do you suggest me to use? bcrypt or PBKDF2?
I was looking for a way to implement them client-side and i thought this way:
The client computes 10.000 interactions of user's password with PBKDF2 and username (or... |
I am reading the birthday attack in [wikipedia][1].
> We consider the following experiment. From a set of $H$ values we
> choose $n$ values uniformly at random thereby allowing repetitions. Let
> $p(n; H)$ be the probability that during this experiment at least one
> value is chosen more than once. This probabil... |
I would ask you some questions about users' password storage in a login system.
1. What algorithm do you suggest me to use? bcrypt or PBKDF2?
I was looking for a way to implement them client-side and i thought this way:
The client computes 10.000 iteractions of user's password with PBKDF2 and username (or ... |
I'm attempting to send a message to a group of recipients, through an untrusted intermediary.
Each of the recipients will have been invited to the group by someone who already has a trusted public key from them.
The best solution I've come up with so far is that a shared secret is created by the first member of ... |
What's your motivation for slow-hashing on the client-side?
- It may well be slower than if performed server side (if you're referring to a browser-based application, and the hashing is done with javascript, then it will certainly be slower, even more so if it's a mobile device)
- it doesn't provide any extra ... |
There are more recent papers that cite Joux and Lucks. Example: "Preimage Attacks against PKC98-Hash and HAS-V", Sasaki et al., uses the Joux-Lucks algorithm to attack two hash functions.
Have you looked at newer papers that cite Joux and Lucks? Have you done a literature search, to find newer papers that cite the... |
What's your motivation for slow-hashing on the client-side?
- It may well be slower than if performed server side (if you're referring to a browser-based application, and the hashing is done with javascript, then it will certainly be slower, even more so if it's a mobile device)
- it doesn't provide any extra ... |
RSA algorithm is use for encryption(plain text to cipher text) and decryption(cipher text to plain text) of data then what is the need of using public key in these sites,why data is encoded as every thing is viewed by every one?
why we need of using public key cryptography in Google, how it provide security ? |
The RSA algorithm is used for encryption (plain text to cipher text) and decryption (cipher text to plain text) of data. What is the need for using public keys in these sites; why is data is encrypted as everything is viewed by everyone?
Why do we need to use public key cryptography in Google; how does it provide se... |
DH key agreement protocols require the participation of both parties, so are only suitable for synchronous connections. Is it possible to implement PFS in a fashion usable for asynchronous protocols, like e-mail, or storage? I'm intuitively thinking not, but I haven't be able to find conclusive proof one way or the o... |
Is asynchronous perfect forward secrecy possible? |
Suppose I am building an encrypted document storage system. Suppose each user has a "user key": a symmetric key. Suppose each document is encrypted with a "document key". So, in order to give a user access to a document, we store a tuple of (user_id, document_id, encrypted_doc_key) where the encrypted document key i... |
Modes for encrypting small binary blobs? |
(significantly reworded this question to fit better into crypto.se).
I have static RSA keypairs for both sides and an encrypted transport that needs symmetric keys, and need to exchange session keys. The library I base this on is OpenSSL, which doesn't seem to have some pre-canned AKC protocol for me to use, so I ha... |
is this authenticated key exchange protocol sound? too complicated? obviously flawed? |
Here is a slightly different approach: The total number of ways to pick $n$ numbers among $H$ value allowing repetition (and with the order of picking counted in) is $A=H^n$. The number of ways to pick without repetitions is $B=\frac{H!}{(H-n)!}.$
Clearly, the probability you want to compute is $(A-B)/A=1-B/A$. Now,... |
So this might sound like a crazy question but bear with me for a minute. I can't find any info on the internet and so am here, although this might have been a good place to start.
I've recently developed an encryption engine using the .net AES managed classes. I use a 256 bit key generated by the Rfc2898DeriveBytes ... |
AES 256 Encryption - Is it really easy to decrypt if you have the key? |
My friend came up with the following idea: assuming we agreed on curve parameters, use the following algorithm for key stretching/derivation from user-entered password.
1. Pad the ascii representation of the password to `n` bits or use any simple hash function, e.g. MD5 to allow passwords of arbitrary length
2. C... |
Your handwriting could be a strong indication that the message was written by you, although that's not unforgeable.
<strike>You can also use personal references or references to earlier, secure communications you had with that person (i.e. meet me at the cafe where we first met).</strike> *(got confused with authent... |
If I understand correctly is to hash your password $pw$ into a point using either $P=Pad(pw)\cdot P_0$ or $P=MD5(pw)\cdot P_0$ and then use $P$ for cryptographic purpose. The exact security of this proposal depends on what you want to do with $P$ exactly. But in some case, this is not secure. Typically, this mechanism ... |
Here is a slightly different approach: The total number of ways to pick $n$ numbers among $H$ value allowing repetition (and with the order of picking counted in) is $A=H^n$. The number of ways to pick without repetitions is $B=\frac{H!}{(H-n)!}.$
Clearly, the probability you want to compute is $(A-B)/A=1-B/A$. Now,... |
My friend came up with the following idea: assuming we agreed on curve parameters, use the following algorithm for key stretching/derivation from user-entered password.
1. Pad the ascii representation of the password to `n` bits or use any simple hash function, e.g. MD5 to allow passwords of arbitrary length
2. C... |
I assume you follow [Kerckhoff's principle](https://en.wikipedia.org/wiki/Kerckhoffs%27s_principle) so the attacker knows the padding scheme and derivation function so the answer is yes, it only takes a few seconds to decrypt and anyone can do it.
If he doesn't know these things, he can find them by trial and error... |
I have been recently going through a question:
http://security.stackexchange.com/questions/15767/what-do-key-size-and-block-size-mean-in-cryptography and it created in me a series of doubts. Referring to the 2nd answer you may find the information that there is 50 percent chance of repetition of a duplicate block if w... |
Why is it said that if we have a duplicate ciphertext block it can leak our information? |
What's your motivation for slow-hashing on the client-side?
- It may well be slower than if performed server side (if you're referring to a browser-based application, and the hashing is done with javascript, then it will certainly be slower, even more so if it's a mobile device)
- it doesn't provide any extra ... |
The relationship between recovering the decryption exponent $d$ and factoring the RSA modulus $n=pq$ is a classical question in cryptography. There are three useful answers:
1. The first answer deals with a slightly different question but is useful to gain some insight into the problem. Assume that we given a bit m... |
I have the following set of equations:
$$M_{1}=\frac{y_1-y_0}{x_1-x_0}$$
$$M_{2}=\frac{y_2-y_0}{x_2-x_0}$$
$$M_1, M_2, x_1, y_1, x_2, y_2, $$ are known and they are chosen from a $$GF(2^m)$$. I want to find $$ x_0,y_0 $$
Does the previous set of equations is solvable?
|
I have the following set of equations:
$$M_{1}=\frac{y_1-y_0}{x_1-x_0}$$
$$M_{2}=\frac{y_2-y_0}{x_2-x_0}$$
$$M_1, M_2, x_1, y_1, x_2, y_2, $$ are known and they are chosen from a $$GF(2^m)$$. I want to find $$ x_0,y_0 $$
Does the previous set of equations is solvable?
And more...
If I have the follo... |
I read ampersand's Question"Necessity for finite field arithmetic and the prime number p in Shamir's Secret Sharing Scheme" where he wrote:
"Shamir's original paper describing a threshold secret sharing scheme states:
To make this claim more precise, we use modular arithmetic instead of real arithmetic. The set ... |
When changing a (small) part of the plaintext of a CBC-encrypted file, how much of the file will have to be rewritten?
My suspicion is that everything after the modified block will have to be decrypted and reencrypted as well, due to the changes of the ciphertext blocks cascading through the rest of the file. |
Can CBC-encrypted files be modified in-place? |
Sorry for the non-specific title, but uh, I couldn't think of anything more descriptive without having a hideously long title.
I'm currently reading the paper '(Leveled) fully homomorphic encryption without bootstrapping', and the following paragraph was near the start -
https://i.stack.imgur.com/ZdDiC.png
W... |
What is meant by this symbol? |
I'm currently reading the paper '(Leveled) fully homomorphic encryption without bootstrapping', and the following paragraph was near the start:
What is meant by the symbol used? Is it merely to represent polynomial time or something else entirely? |
What is meant by $\tilde\Omega(\lambda^4)$? |
Is there a significantly advantage to these data structures, or is it simply the status-quo and the easiest to use for describing constructions? |
Why do fully homo-morphic constructions use 'ring' or 'lattice' structures? |
According to Wikipedia, the IND-CPA game is:
> The challenger generates a key pair PK, SK based on some security
> parameter k (e.g., a key size in bits), and publishes PK to the
> adversary. The challenger retains SK. The adversary may perform a
> polynomially bounded number of encryptions or other operations.
... |
Why is asymmetric encryption IND-CPA? |
This isn't just limited to asymmetric schemes; in any chosen-plaintext attack, even for symmetric ciphers, the attacker can (by definition of the CPA game) compute as many encryptions as they like (limited to polynomial time, of course). Formally, we say the adversary is given access to an "encryption oracle."
Anywa... |
Here's a scenario I want to handle with a secret sharing scheme:
1. Alice wants to share the secret _S_ with Bob, Charlie and Dave. Alice generates private shares
based on _S_ for Bob, Charlie and Dave, and communicates them to their intended recipients via a secure
channel.
2. Alice generates a parame... |
Here's a scenario I want to handle with a secret sharing scheme:
1. Alice wants to share the secret _S_ with Bob, Charlie and Dave. Alice generates private shares
based on _S_ for Bob, Charlie and Dave, and communicates them to their intended recipients via a secure
channel.
2. Alice generates a parame... |
Here's a scenario I want to handle with a secret sharing scheme:
1. Alice wants to share the secret $S$ with Bob, Charlie and Dave. Alice generates private shares
based on $S$ for Bob, Charlie and Dave, and communicates them to their intended recipients via a secure
channel.
2. Alice generates a parame... |
I am reading biclique cryptanalysis of the full AES paper...what they mean by ' sharing active S-boxes'? how this concept can be advantageous to make a biclique?If there is someone who read this paper please help me ..thank you |
Real-world encryption systems are often not broken algorithmically but because the implementation has a bug. Sometimes the bug only happens in circumstances that could not have been foreseen, such as weak random numbers, or an error in a library causing e.g. predictable IVs.
So I wonder, are there workable methods o... |
Assume a simple protocol for authentication - one side sends a randomly generated challenge string and encrypts it with RSA.
The receiver decrypts it and replies with a hash of the challenge, proving that he owns the private key (and nothing more).
My question: is it safe to also use parts of the same random chal... |
Assume a simple protocol for authentication - one side sends a randomly generated challenge string and encrypts it with RSA.
The receiver decrypts it and replies with a hash of the challenge, proving that he owns the private key (and nothing more).
My question: is it safe to also use parts of the same random chal... |
According to Wikipedia, the IND-CPA game is:
> The challenger generates a key pair PK, SK based on some security
> parameter k (e.g., a key size in bits), and publishes PK to the
> adversary. The challenger retains SK. The adversary may perform a
> polynomially bounded number of encryptions or other operations.
... |
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