instruction stringlengths 15 30k |
|---|
Where is the signature date saved in a digitally signed file? |
Is there a way to generate **n** strings with the same MD5 hash?
|
So I have been doing for the last couple of days comparison between Feistel cipher and Substitution-permutation network. Now I can say I know a lot about them and their similarities and differences but there is still one more thing I would like to know and I can't find it anywhere.
The thing is I don’t know how many... |
In the key generation step of [paillier][1] cryptosystem ,
In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal [length][2] primes.
Instead of taking equal length primes , is there any time efficient method to assure
$pq,(p-1)(q-1)$ are relatively prime ? Or is it mandatory to take equal length pri... |
How can I know when a file was signed? |
With AES-CTR the computation time to encrypt a message of lengh $n$ blocks is $n$ computations of the block cipher.
What is the running time to encrypt a message of $n$ bits using a stream cipher, like Salsa, Snow, trivium or any other stream cipher ?
Thank you. |
I have been reading on the polynomial representation of the AES Sbox in the PDF “Essential Algebraic Structure Within the AES” by Murphy and Robshaw (www.isg.rhul.ac.uk/~sean/crypto.pdf) on page 7, that the affine transformation can be represented as $f(a) = \sum^7_{k=0} \lambda_ka^{2^k}$ where $(\lambda_0, \lambda_1, ... |
Why is AES considered to be secure when encrypting large files since the algorithm is a block cipher?
I mean, if the file is larger than the block size, the file will be broken down to fit the blocks. Then the same key is used to encrypt each block of the file. And as I know it, using the same key to encrypt multipl... |
How can AES be considered secure when encrypting large files? |
Encrypting big amounts of data is no problem for block cipher - if you remember a few important things.
You can't encrypt plaintext which is bigger than the block size. You need to do some addition work. Most cipher operation modes first divide the plaintext into blocks of the size of the cipher. Now you can do diff... |
I had a small discussion with my friend on clubbing two 64 bit key based encryption algorithms today.
Say I have a plain text of 64 bits which I want to encrypt. My Key size is 128 bits.
I will use standard DES algorithm with first 64 bits on plain text to encrypt it.
With remaining 64 bits of key I will apply b... |
I had a small discussion with my friend on combining two encryption algorithms based on 64-bit keys.
Say I have a plain text of 64 bits which I want to encrypt. My Key size is 128 bits. I will use the standard DES algorithm with the first 64 bits of the key to encrypt plaintext. With the remaining 64 bits of key, I ... |
i was playing with vernam cipher on some online converter. But when i tried to encrypt my message string with numbers, it remained unchanged. Moreover, it was ignoring numbers and was encrypting as some alphabet appears in the key.
![enter image description here][1]So, can we use numbers as pad in vernam cipher - w... |
Can we use numbers as pad in vernam cipher - why or why not? |
I was playing with the Vernam cipher on some online converter.
<br>
But when I tried to encrypt my message string with numbers, it remained unchanged.
<br>
Moreover, it was ignoring numbers and was encrypting as some alphabet appears in the key.
![enter image description here][1]
So, can we use numbers as a ... |
Can we use numbers as a pad in the Vernam cipher - why or why not? |
For example "Google Internet Authority G2"?. I thought it was another way of specifying Class 2 (for organizations, for which proof of identity is required) but then see certificates such as "VeriSign Class 3 Public Primary CA - G2".
Thanks in advance. |
What does "G2" mean when used with X509 certficates and certificate authorities? |
For example "Google Internet Authority G2"?. I thought it was another way of specifying Class 2 (for organizations, for which proof of identity is required) but then see certificates such as "VeriSign Class 3 Public Primary CA - G2".
It couldn't be something so simple such as Generation 2 could it? Hope someone who ... |
In the key generation step of [paillier][1] cryptosystem ,
In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal [length][2] primes.
Instead of taking equal length primes , is there any time efficient method to generate $p,q$ that assures
$pq,(p-1)(q-1)$ are relatively prime ? Or is it mandatory to ... |
In the key generation step of [paillier][1] cryptosystem ,
In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal [length][2] primes.
Instead of taking(length as parameter to generate $p,q$) equal length primes , is there any time efficient method to generate $p,q$ that assures
$pq,(p-1)(q-1)$ are re... |
What is the name of an algorithm that hashes itself embedded in a larger body of data to convergence? |
What is the name of an algorithm that hashes itself embedded as a "signature" in a larger body of data and results it itself for nontrivial solutions? |
What is the name of an algorithm that hashes itself as an embed of larger set of hashed data that results back to the hash? For instance where f(x) is the hashed result and x is the dataset, and f(x)=foobar, x={foobar....., ...foobar....,....foobar} |
What is the name of an algorithm that hashes its result as an embed of larger set of data that results back to the hash? For instance where f(x) is the hashed result and x is the dataset, and f(x)=foobar, x={...foobar....} |
So, I have been assigned an assignment where I had to solve a Vigenere cipher. Following along with this webpage ( http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/ ) I managed to get all the way the chi-squared step. But, that is the problem. Upon trying to code this, I... |
So I'm currently doing the Dan Boneh online Crypto course.
In the last problem set there was a question on AACS for DVDs and wondered if a similar method could be used for music.
- Have the music industry ever attempted something along these lines?
- What are the limitations?
- Are there any crypto-systems i... |
How Could the Music Industry Go About Implementing Crypto? |
DNSSEC, ECDHE, RSA, even SSH and all other important specifications, protocols that we rely on and advise people to use them, they use Public key infrastructure.
**Question:** Why do we still use, advise PKI if it's a fact (not just theory) that quantum computing will break PKI in less then 10-20 years? |
Why are we advising PKI if we know that quantum computers will break them? |
$ openssl version
OpenSSL 1.0.1 14 Mar 2012
$
$ openssl ciphers
ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:SRP-DSS-AES-256-CBC-SHA:SRP-RSA-AES-256-CBC-SHA:SRP-AES-256-CBC-SHA:DHE-DSS-AES256-GCM-SHA384:... |
Are there any ciphers that will not be affected by the post-quantum world? |
Are there any SSL cipher suites that will not be affected by the post-quantum world? |
Are there cryptographic hash functions that have homomorphism-like properties?
E.g. satisfying following relation $h(a || b) = h(a) · h(b)$, where $h(x)$ is hash function itself, $x || y$ is concatenation and $x · y$ is some hash-specific combination function making single hash given two of them. If that makes any d... |
Are there cryptographic hash functions with homomorphic properties? |
So, I have been assigned an assignment where I had to solve a Vigenere cipher.
Following along with [this webpage]( http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/ ) I managed to get all the way to the chi-squared step. But, that is the problem. Upon trying to code ... |
I am trying to implement the [Fluhrer, Mantin and Shamir attack][1], one of the ways to break WEP. I seem to have hit on a problem. I have no idea whether or not it is a programming error, or if I don't understand the practical part of the attack properly.
Can I get some verification that I understand how to use it ... |
I am trying to implement the [Fluhrer, Mantin and Shamir attack][1], one of the ways to break WEP. I seem to have hit on a problem. I have no idea whether or not it is a programming error, or if I don't understand the practical part of the attack properly.
Can I get some verification that I understand how to use it ... |
I am trying to implement the [Fluhrer, Mantin and Shamir attack][1], one of the ways to break WEP. I seem to have hit on a problem. I have no idea whether or not it is a programming error, or if I don't understand the practical part of the attack properly.
Can I get some verification that I understand how to use it ... |
I am trying to implement the [Fluhrer, Mantin and Shamir attack][1], one of the ways to break WEP. I seem to have hit on a problem. I have no idea whether or not it is a programming error, or if I don't understand the practical part of the attack properly.
Can I get some verification that I understand how to use it ... |
Recently, I'm reading [Non-Interactive Key Exchange][1], in the section 4.2(Towards a factoring-based scheme in the standard model,Page 10), the authors uses
$$t\gets ChamH_{hk}(Z||ID;r);\\
Y\gets u_0u_1^tu_2^{t^2};X=Y^x$$
this way, I don't understand why the authors use the chameleon hash function like this, w... |
Help to understand the chameleon hash function? |
![Added Details][1]I am studying DES for my Cryptoexam .As far as I understood , the initial plaintext is permuted and then the left half is called L0 and Right half is called R0.
After that for each round the process is as follows
L(i) = R (i-1)
R(i) = L(i-1) XOR f(R(i-1), K(i))
This relation holds till ... |
Does NTRU provides Perfect Forward Secrecy if the world would use it in an HTTPS connection? |
Does NTRU provide Perfect Forward Secrecy? |
Which key is more secure:
1. A password: "123456" (length 6) is entered into PBKDF2 ---> Produced key
2. A password: "XK6f+d" (length 6) is entered into PBKDF2 ---> Produced key
3. A password: "123456789" (length 9) is entered into PBKDF2 ---> Produced key
4. A password: "dYn5p78+/" (length 9) is entere... |
I know that PBKDF2 is very useful for generating strong keys. I'm trying to know is there any additional contribution of the given password to produce even stronger keys.
Which key is more secure:
1. A password: "123456" (length 6) is entered into PBKDF2 ---> Produced key
2. A password: "XK6f+d" (length 6... |
Does NTRU* provides Perfect Forward Secrecy if the world would use it in an HTTPS connection?
*https://en.wikipedia.org/wiki/NTRU |
Does [NTRU][1] provide Perfect Forward Secrecy if the world would use it in an HTTPS connection?
[1]: https://en.wikipedia.org/wiki/NTRU |
Recently I watched the movie 'The Prestige' again but this time the cipher diary impressed me very well. I like to create my own cipher for my diary because I have some time to kill everyday after deactivating facebook.
So If I create my own substitution table like `'Vigenère_cipher'`, and use a `different key for... |
How hard to break a cipher if it have a different key for each word? |
Recently I watched the movie 'The Prestige' again but this time the cipher diary impressed me very well. I like to create my own cipher for my diary because I have some time to kill everyday after deactivating facebook.
So If I create my own substitution table like `'Vigenère_cipher'`, and use a `different key for... |
Has anyone come across any implementations of Ntru TLS? I'm working a project for uni that does quantum secure encryption. It relies on a mix of Ntru & AES, but I can't find an implementation of Ntru TLS anywhere. (CyaSSL claims to have one but it needs a license to compile, I've contacted them, waiting to hear back)
... |
I saw this answer at this site about decoding a 3-rotor Engima machine's settings:
http://crypto.stackexchange.com/questions/13150/how-cryptographically-secure-was-the-original-ww2-enigma-machine-from-a-modern/13153#13153
And did some math for the decoding method in the highest ranked answer:
$2^{20}$ * $2^{19... |
> "Create a random key for CCPA2 scheme, encrypt m, send it along with a
> PK encryption of the symmetric key. "
Say in the process, the KDF is HMAC, then:
1. get a random key (128-bit)
2. C1 = encrypt the message ``"Hello World"`` using AES
3. C2 = is a tuple of E_pk(random_key), and HMAC(random_key, ra... |
As mentioned in [wikipedia][1] there are many Partial Homomorphic Encryption(PHE) scheme like RSA, Elgamal, Pailler etc.
But out of them only unpadded RSA scheme seems to be partial(multiplicative) homomorphic encryption scheme.
Are there any PHE schemes that retain their property even after padding ?
[1]... |
I have heard good things about the emerging ["FIDO U2F" standard][1]. I am especially interested in having a JavaScript API for cryptographic functions that I can access through a plug-in in a browser.
However, so far all my efforts to obtaining a physical hardware token supporting the FIDO U2F specs for testing wer... |
Will I be able to (ab)use a FIDO U2F compliant hardware token to decrypt data? |
How hard to break a cipher if it has a different key for each word? |
The common way to store passwords in web applications is this form:<br>
$$hash(password||salt)$$
Does it make sense to store them in the following form instead:?
$$hash_1(hash_2(...hash_n(password||salt)))$$
Where $n$ is the order of a $10^9$.
<b>The main advantage of this method is the difficulty in decryptin... |
Instead of rolling your own, you should use [PBKDF2][1], which does what you try, but right. Alternatively use scrypt or maybe bcrypt, they try to be more expensive on GPUs and custom cracking hardware.
> (this will take about a million times longer compared to the usual method of calling a single hash function)
... |
Instead of rolling your own, you should use [PBKDF2][1], which does what you try, but right. Alternatively use scrypt or maybe bcrypt, they try to be more expensive on GPUs and custom cracking hardware.
> (this will take about a million times longer compared to the usual method of calling a single hash function)
... |
Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
My reasoning is that the attacker doesn't know all the plaintext, so by having a hash, the attacker will be able to change the message, but will be unable to recalculate the hash.
Are there any flaws in my re... |
Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity? |
> Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
Not in the sense of authentication. Such a construction is [malleable][1] for many reasonable encryption algorithms. It also leaks the plaintext to anyone who can guess it, since they can calculate $h(P_i)$ fo... |
> Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
Not in the sense of authentication. Such a construction is [malleable][1] for many reasonable encryption algorithms. It also leaks the plaintext to anyone who can guess it, since they can calculate $h(P_i)$ fo... |
Implementing a web app where the server cannot decrypt its own data? |
I am implementing an ECDSA NIST test vectors verification application. The test vectors are taken from http://csrc.nist.gov/groups/STM/cavp/#09.
One of the test vectors is given below:
P-192 SHA1
Msg = 608079423f12421de616b7493ebe551cf4d65b92
d = e14f37b3d1374ff8b03f41b9b3fdd2f0ebccf275d66... |
> Either an RSA key pair is provided by the customer (high security, less convenient) OR a key pair is generated by the server and sent to the client (customer has to trust that we won't store the private key, but more convenient)
Any reason not to generate a key pair in the client app? Nowadays even browsers should... |
I'm trying to interoperate with a web service by reverse-engineering it. Currently, when sending a POST request, it encrypts the form data one-by-one with a 'RSA' function. But it's rather weird as everywhere else i've tried to use these values have given me errors. It's using this library: https://code.google.com/p/pa... |
Suppose we are aiming to solve the discrete logarithm problem $\alpha^x=\beta$ in some cyclic group $G=<\alpha>$. Then we are looking for a (uniformly) random sequence of elements of the form $\alpha^{a_{i}}\beta^{b_{i}}$, $i=0,1,2,...$ so that we can invoke the 'Birthday Paradox'. Pollard suggested a function which ap... |
We all know that in a public key cryptosystem, given a public key it is extremely hard to compute private key from it.
Is it the same case in reverse?
Given a private key, how easy is it to compute public key out of it?
It would be great to have answers with respect to an algorithm like RSA. |
Why would an RSA library tell me that the public key must be at least 512 bits in size? |
> We all know that in a public key cryptosystem, given a public key it is extremely hard to compute private key from it.
> Is it the same case in reverse?
Not in general. For example, in Diffie-Hellman the public key is just a constant raised to a private number, modulo another constant. In some elliptic curve al... |
I have a public key in the following (format-neutral; the type is specified by the DER bytes) format:
$ cat pubkey.der | openssl asn1parse -inform der -i
0:d=0 hl=4 l= 290 cons: SEQUENCE
4:d=1 hl=2 l= 13 cons: SEQUENCE
6:d=2 hl=2 l= 9 prim: OBJECT :rsaEncryption
... |
What is the technical name for a public key in DER format? |
What is the technical name for a public key container in DER format? |
I am new to cryptography so my apologies for asking such a basic question.
I was reading up on <a href="http://en.wikipedia.org/wiki/Keystream">keystream</a> when i came upon the definition of it
> A keystream is a stream of random or pseudorandom characters that are
> combined with a plaintext message to produc... |
I've bee learning about Rabin's cryptosystem, and I already know that Rabin's cryptosystem is vulnerable to a chosen-ciphertext attack, but I was wondering if it's also vulnerable against known-plaintext attacks? I think it's not, but I'm not sure. I would appreciate if someone could clear this up for me. |
Is Rabin's cryptosystem secure against known-plaintext attacks? |
I am new to cryptography so my apologies for asking such a basic question.
I was reading up on <a href="http://en.wikipedia.org/wiki/Keystream">keystream</a> when I came upon the definition of it:
> A keystream is a stream of random or pseudorandom characters that are
> combined with a plaintext message to produ... |
Are password salts equivalent to keystream? |
So I understand the two concepts:
- (Strong) collision resistance: it is infeasible to find a pair $x \neq x'$ such that $h(x) = h(x')$
- Weak collision resistance / 2nd-preimage resistance: for all $x \in D$ it is infeasible to find $x' \neq x$ such that $h(x)=h(x')$
But I'm confused as to how to negate the t... |
The difference between being not strongly collision resistant, and not weakly collision resistant? |
I've bee learning about Rabin's cryptosystem, and I already know that Rabin's cryptosystem is vulnerable to a chosen-ciphertext attack, but I was wondering, is it also vulnerable against known-plaintext attacks? I think it's not, but I'm not sure. I would appreciate if someone could clear this up for me. |
I'm reading the salsa20 spec (sorry for the newbie question, i'm really a newbie here). Every paragraph ends with : "this operation is invertible", I suppose the whole salsa20 algorithm is.
1. If I use salsa20 in bloc cipher CTR mode, this property does not seems mandatory to me, am I right?
2. As such, any crypt... |
salsa20 is invertible, useless in CTR mode? |
In the Bouncy Castle libraries, the GCM cipher has an interesting property that does not seem described in the GCM papers (neither the NIST or the original paper):
> Some AAD was sent after the cipher started. We determine the difference b/w the hash value we actually used when the cipher started (`S_atPre`) and the... |
> Every paragraph ends with : "this operation is invertible", I suppose the whole salsa20 algorithm is.
The Salsa20 quarterround, and thus rowround, columnround and doubleround are invertible. However, the whole Salsa20 core is *not* because the initial state is added to the state after iterating the rounds (cf. pag... |
How does Salsa20 work?
---
1. The basic building block of salsa20 is a fixed 512 bit permutation. This is similar to a block cipher with a fixed and publicly know key (or a zero bit key if you prefer). Since it has no key input, you can't use it with block cipher modes of operation.
2. The next step in Salsa20 i... |
I'm digging into the several algorithms for building **(Minimal) Perfect Hash Functions**. It seems that the recent works provide quite a few very efficient algorithms.
However, I'm wondering how a (M)PHF behaves in case of **unsuccessful searches** and what level of **privacy** can guarantee:
1. What happens if... |
I prefer using definitions that explicitly specify who does what.
Weak collision resistance: After Bob creates some message x1, it is "computationally infeasible" for an attacker Mallory to compute some other message x2 such that h(x1) == h(x2).
Strong collision resistance: It is "computationally infeasible" for ... |
In the Bouncy Castle libraries, the GCM cipher implementation has an interesting property that does not seem described in the GCM papers (neither the NIST or the original paper):
> Some AAD was sent after the cipher started. We determine the difference b/w the hash value we actually used when the cipher started (`S_... |
I'm really in trouble! I'm trying to understand how the T-tables in AES encryption work. But I don't know if I get the point.
What I understood is that they are used to reduce the whole computation of the iteration of AES just looking at the T-boxes and the XOR operation.
Now, what I got is that:
State ... |
I'm really in trouble! I'm trying to understand how the T-tables in AES encryption work. But I don't know if I get the point.
What I understood is that they are used to reduce the whole computation of the iteration of AES just looking at the T-boxes and the XOR operation.
Now, what I got is that:
State ... |
(You should take a look at [page 18 of FIPS 197][1] where it describes the MixColumns transform).
You're close. Swap the order of your matrices so that you have:
|02 03 01 01| |d4 e0 b8 1e|
|01 02 03 01| |bf b4 41 27|
|01 01 02 03| |5d 52 11 98|
|03 01 01 02| |30 ae f1 e5|
And then y... |
(You should take a look at [page 18 of FIPS 197][1] where it describes the MixColumns transform).
You're close. Swap the order of your matrices so that you have:
|02 03 01 01| |d4 e0 b8 1e|
|01 02 03 01| |bf b4 41 27|
|01 01 02 03| |5d 52 11 98|
|03 01 01 02| |30 ae f1 e5|
And then y... |
i want implement an article that is about make secure biometric template using fuzzy commitment . this schema used in many paper.I'm wondering is there any open source implementation of this schema available?especially in `matlab` ? |
The definition of perfect hash functions do not have any security/cryptographic requirements. For example, the hash function that simply outputs the first n bits of any string is a perfect hash function on the set of n bit strings. Obviously this function does not hide the input at all.
So the answer to your questi... |
I'm digging into the several algorithms for building **(Minimal) Perfect Hash Functions**. It seems that the recent works provide quite a few very efficient algorithms.
However, I'm wondering how a (M)PHF behaves in case of **unsuccessful searches** and what level of **privacy** can guarantee:
1. What happens if... |
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