instruction stringlengths 15 30k |
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What is the computational time to break McEliece on a quantum computer?
I've seen thet polynomial time algorithms exist but for special conditions. What about the general case? |
How can I calculate the Rijndael SBox? |
I would like to implement the *Rijndael subBytes()* operation using calculation instead of tables, because I like to play with this on different *wordsizes*, as an academical exercice, to see what the table would look like.
The first part is a multiplicative inverse in the polynomial binary finite field, isn't it? T... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community..
Here's the link to the project:
http://www.codeproject.com/Articles/790798/Random-Thoughts
It is written in C#, code is clean and well commented.
The design criteria:
1. The same seed ... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
What is the computational time to break McEliece on a quantum computer?
I've seen that polynomial time algorithms exist, but for special conditions. What about the general case? |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
Is there any relationship between the RSA keypair standard and RSA security?
Keypair: http://en.wikipedia.org/wiki/RSA_(cryptosystem)
Security: http://en.wikipedia.org/wiki/RSA_Security
If not, can anyone explain what RSA stands for (so I can keep the two seperate)? |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
When using PBKDF2, is there a practical upper limit to the iteration count above which we lose security?
**Note**: If you answer: "No" - That's fine. But if you answer: "There can't be an upper limit" - Consider the case of 2^256 iterations using SHA-256.
|
Is there a practical upper limit for password rehashing? |
> When using PBKDF2, is there a practical upper limit to the iteration count above which we lose security?
No.
There is a limit above which you gain no security, but it isn't practical. It's on the order of $2^{128}$ iterations for PBKDF2-HMAC-SHA-2, or $2^{80}$ if you use SHA-1 as the HMAC hash. For an explanati... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
When using PBKDF2, is there a practical upper limit to the iteration count above which we lose security?
**Note:** If you answer *“No”*, that's fine. But if you answer: *“There can't be an upper limit“*, Consider the case of $2^{256}$ iterations using SHA-256.
|
I would like to implement the Rijndael `subBytes()` operation using calculation instead of tables, because I like to play with this on different *wordsizes*, as an academical exercice, to see what the table would look like.
The first part is a multiplicative inverse in the polynomial binary finite field, isn't it? ... |
How do I choose the best 3*3 s-boxes? |
Is it mathematically possible to take a SHA256 hash and turn it into a 0-99 number where each number in 0-99 range is equally likely to be picked?
As a 256 bit hash means the highest value possible is 2^256, this is not a nice or "round" number for the purposes of simplifying a hash down to ranges more natural for h... |
First, the obvious advice is not to use this in practice. Rolling your own is fine for learning, but you should use standard primitives when you need actual security. E.g. one from [SP 800-90A][1] which poncho linked in comments.
Now, some observations. I haven't read all your code, so I may misunderstand things.
... |
I'm pretty sure that they store only the hash.
They can detect that you didn't change enough characters in the following way:
When you provide a new password, the system generates several passwords that similar to the new password, by changing some characters.
Then it calculates the hash of each similar password... |
How can a vigenere cipher be broken if the message is short? |
Here is a somewhat silly and atypical problem I am currently facing. Usually, when it comes to hashes, one is bothered with finding collisions and preimages. My problem is, I need to find the IHV used to initialise the word buffers. The message and the hash function output are considered to be known.
Is there a non... |
I was watching a Stanford lecture on [Vigenère cipher](http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher) and in it the professor said that – to break the cipher – we assume the length of the key is known. We then break the cipher into groups of this known length and then pick up (successively) the first, second, etc. ... |
How can a Vigenère cipher be broken if the message is short? |
> Alice pays Bob $5/month to host a gigantic file for her. She wants to
> occasionally verify that Bob is actually hosting the file. To do this,
> she selects random blocks from the file, and challenges Bob to hash
> those same blocks with her chosen salt. The digests should match.
This is a solved problem because Bob... |
What is a proof of data possession that accounts for fake mirrors? |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
For breaking a Vigenere cipher by frequency analysis the length of the cipher text alone is not the crucial part. What really matters is the **proportion** cipher_text_len/key_len, as this indicates how many characters of the clear text are encoded by the same character of the key.
For the example you provided this... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
I was watching a Stanford lecture on [Vigenère cipher](http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher) and in it the professor said that – to break the cipher – we assume the length of the key is known. We then break the cipher into groups of this known length and then pick up (successively) the first, second, etc. ... |
In openSSL, when generate RSA keys, if q is bigger than p,the exchange them,why is that? |
In RSA,why p must be bigger than q where n=p*q? |
In openSSL, when generate RSA keys, if q is bigger than p,then exchange them,why is that? |
There's no real difference between $p$ and $q$ in RSA. It looks like OpenSSL just has the agreement "$p$ has to be bigger than $q$" for conveniences. One of the numbers has to be bigger than the other (otherwise they would be the same number, and $p = q$ is very bad in RSA).
Just use two examples: $p = 13$ and $q = ... |
In openSSL, during RSA key generation if $q$ is bigger than $p$, they exchange them. Why is that? |
In RSA, why does $p$ have to be bigger than $q$ where $n=p \times q$? |
In openSSL – during RSA key generation – if $q$ is bigger than $p$, they exchange them. Why is that? |
Randomness is not a property of strings of bits (or characters of any sort). Rather it is a property of the process that generates those strings. However, it is convenient to conflate the string with the thing that produced the string, and thus to speak about strings being *“random”* or *“not random”*.
The string ... |
> How to prove the security of the PRNG?
My best advice would be to start with the test suite NIST describes in ["A Statistical Test Suite for Random and Pseudorandom Number Generators for Cryptographic Applications"](http://csrc.nist.gov/publications/nistpubs/800-22-rev1a/SP800-22rev1a.pdf) (PDF).
It’s a batter... |
> How to prove the security of the PRNG?
My best advice would be to start with the test suite NIST describes in ["A Statistical Test Suite for Random and Pseudorandom Number Generators for Cryptographic Applications"](http://csrc.nist.gov/publications/nistpubs/800-22-rev1a/SP800-22rev1a.pdf) (PDF).
It’s a batter... |
> What tests can I do to ensure my PRNG is working correctly?
That depends on what exactly you mean by *“working correctly”*.
You can do statistical tests to check for various statistical flaws your random number generator might be subject to, but ***you have be aware of the fact that statistical testing cannot ... |
> What tests can I do to ensure my PRNG is working correctly?
That depends on what exactly you mean by *“working correctly”*.
You can do statistical tests to check for various statistical flaws your random number generator might be subject to, but ***you have be aware of the fact that statistical testing cannot ... |
> What tests can I do to ensure my PRNG is working correctly?
That depends on what exactly you mean by *“working correctly”*.
You can do statistical tests to check for various statistical flaws your random number generator might be subject to, but ***you have be aware of the fact that statistical testing cannot ... |
> What tests can I do to ensure my PRNG is working correctly?
That depends on what exactly you mean by *“working correctly”*.
You can do statistical tests to check for various statistical flaws your random number generator might be subject to, but ***you have be aware of the fact that statistical testing cannot ... |
> How to prove the security of the PRNG?
My best advice would be to start with a statistical test suite like the one NIST describes in ["A Statistical Test Suite for Random and Pseudorandom Number Generators for Cryptographic Applications"](http://csrc.nist.gov/publications/nistpubs/800-22-rev1a/SP800-22rev1a.pdf) (... |
Before answering your questions:
GCM is an authentication encryption mode of operation, it is composed by two separate functions: one for encryption (AES-CTR) and one for authentication (GMAC).
It receives as input:
1. a Key
2. a unique IV
3. Data to be processed only with authentication (associated data)
... |
In [RFC 3526](http://www.ietf.org/rfc/rfc3526.txt) there are a series of primes listed as standard parameters used for Diffie-Helman. The primes are list in two formats. One is the long format, where the number is given in hex. For example:
FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
29024E08 ... |
I am trying to understand why the constants differ in this SHA1 implementation:
1. https://code.google.com/p/crypto-js/source/browse/tags/3.1.2/src/sha1.js
this._hash = new WordArray.init([
0x67452301, 0xefcdab89,
0x98badcfe, 0x10325476,
0xc3d2e1f0
]);
2.... |
I am doing a small project in ECC. I have used the below equation for converting Projective to Jacobian directly.
$$ D = AC $$
$$ E = BC ^2 $$
$$ F = C $$
and also the below equation is derived for Jacobian to Projective directly.
$$ A = DF $$
$$ B = E $$
... |
Is jacobian to projective conversion unique? |
I am doing a small project in ECC. I have used the below equation for converting Projective to Jacobian directly.
$D = AC$
$E = BC^{2}$
$F = C$
and also the below equation is derived for Jacobian to Projective directly.
$A = DF$
$B = E$
$C ... |
The Wikipedia [*“Key Size”*](http://en.wikipedia.org/wiki/Key_size) article states:
> The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. For example, Triple DES has a key size of 168 bits but provides at most 112 bits of security, sin... |
Effective security of block cipher – equal the key size, or half the key size? |
I am doing a small project in ECC. I have used the following equation for converting Projective to Jacobian coordinates:
$$D = AC\\
E = BC^{2}\\
F = C$$
and also the following equation to convert Jacobian to Projective coordinates:
$$A = DF\\
B = E\\
C = F^{3}$$
where $(A,B,C)$ represents a point in Pro... |
How works the public key recovering from an ECDSA signature? |
How does recovering the public key from an ECDSA signature work? |
Does [CCA][1] security imply [authenticated encryption][2]?
[1]: http://en.wikipedia.org/wiki/Chosen-ciphertext_attack
[2]: http://en.wikipedia.org/wiki/Authenticated_encryption |
Does CCA security imply authenticated encryption? |
The Wikipedia [*“Key Size”*](http://en.wikipedia.org/wiki/Key_size) article states:
> The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. For example, Triple DES has a key size of 168 bits but provides at most 112 bits of security, sin... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
As I understand it, CTS pads the last block and swaps it with the second last to compensate for a partial block of data. I have written a DRBG using AES-CBC that only accepts an input size that falls on the block boundary. So, my question is: is CTS really necessary here? I can't imagine a way in which it's absence wil... |
I've just about done tinkering with an open source DRBG, and I sure would appreciate a bit of advice from this community. [Here's the link to the project](http://www.codeproject.com/Articles/790798/Random-Thoughts), hosted at codeproject.com.
It is written in C#, the code is clean and well commented.
The design ... |
As I understand it, CTS pads the last block and swaps it with the second last to compensate for a partial block of data. I have written a DRBG (Deterministic Random Bit Generator) using AES-CBC that only accepts an input size which falls on the block boundary.
Is CTS really necessary here? I can't imagine a way in ... |
In the answer to the question [What exactly is a negligible (and non-negligible) function?][1]
There is a part in the explanation that to as far as my knowledge goes is conflicting.
> But instead of brute force, the adversary can guess (a polynomial number of) random values and hope to chance upon the right one.
... |
The Wikipedia [*“Key Size”*](http://en.wikipedia.org/wiki/Key_size) article states:
> The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … **Most symmetric-key algorithms in common use are designed to have security equal to their key ... |
The Wikipedia [*“Key Size”*](http://en.wikipedia.org/wiki/Key_size) article states:
> The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most symmetric-key algorithms in common use are designed to have security **equal to their ... |
In the answer to the question [“What exactly is a negligible (and non-negligible) function?”][1]
There is a part in the explanation that – as far as my knowledge goes – is conflicting:
> But instead of brute force, the adversary can guess (a polynomial number of) random values and hope to chance upon the right on... |
Based on the attached table as a part of a proposed key agreement scheme in the following link, the authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve group) is about 1000% more efficient than a pairing based one, while there are many pairing-ba... |
Based on the table below, which is [**available at sciencedirect.com**](http://www.sciencedirect.com/science/article/pii/S0020025510001519) as a part of a proposed key agreement scheme, the authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve grou... |
Based on the table below, which is [**available at sciencedirect.com**](http://www.sciencedirect.com/science/article/pii/S0020025510001519) as a part of a proposed key agreement scheme, the authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve grou... |
Based on the table below, which is [**available at sciencedirect.com**](http://www.sciencedirect.com/science/article/pii/S0020025510001519) as a part of a proposed key agreement scheme, the authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve grou... |
If you can use something more lightweight than pairings then course you skip pairings. There is a technical property of pairings than is not the case with other crypto primitives. And this is the evaluation of multiplications on the exponent that cannot be achieved in other cases. If you need some sort of summation the... |
I read the claim, without proof, that it is possible to construct a next bit predictor for any PRNG given an oracle distinguisher for that PRNG and vice versa. How do I proof that?
An distinguisher takes a bitstring and tells you if it was generated by the PRNG or not.
A next bit predictor takes a bitstring and te... |
some authors claimed that computational performance of a pairing-fee scheme (based on scalar multiplication over an elliptic curve group) is about 1000% more efficient than a pairing based one
I would like to know: is there any advantage for a pairing-based scheme?
|
I am wondering: what is the most common, or most used, block cipher mode used that goes with CTS (CypherText Stealing)?
Is it [tag:ebc] or [tag:cbc]? |
The Wikipedia [*“Key Size”*](http://en.wikipedia.org/wiki/Key_size) article states:
> The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most symmetric-key algorithms in common use are designed to have security **equal to their ... |
On the [Diceware][1] page is this little gem:
> For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at random adds about 10 bits of entropy.
By that statement, does that mean adding a random character to a random positi... |
What is the entropy per Diceware word if a random special character is inserted into a random position in the word? |
On the [Diceware][1] page is this little gem:
> For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at random adds about 10 bits of entropy.
By that statement, does that mean adding a random character to a random positi... |
On the [Diceware][1] page is this little gem:
> For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at random adds about 10 bits of entropy.
By that statement, does that mean adding a random character to a random positi... |
On the [Diceware][1] page is this little gem:
> For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at random adds about 10 bits of entropy.
By that statement, does that mean adding a random character to a random positi... |
What is the entropy per Diceware word if a random symbol is inserted into a random position in the word? |
On the [Diceware][1] page is this little gem:
> For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at random adds about 10 bits of entropy.
By that statement, does that mean adding a random character to a random positi... |
If you add a truly random character into a truly random position of a word, you get "entropy of position" + "entropy of character" as addition to the entropy of the word. (Not exactly, it's a bit less). The entropy of character is the size of the possible characters. 64 possible characters would be $log2(64) = 6$ bits ... |
> By that statement, does that mean adding a random character to a random position in a Diceware word adds 10 bits to each word?
No. The ten bit estimate is for adding a random symbol from the 36-item table to a random position *in the passphrase*. The entropy in the character choice is about five bits and the entro... |
> By that statement, does that mean adding a random character to a random position in a Diceware word adds 10 bits to each word?
No. The ten bit estimate is for adding a random symbol from the 36-item table to a random position *in the passphrase*. The entropy in the character choice is about five bits and the entro... |
[What is Attribute Based Encryption?](http://crypto.stackexchange.com/q/17893/13022) has a nice explanation what both forms (Ciphertext-policy Attribute-based Encryption and Key-policy Attribute-based Encryption) are.
My question is: what is the motivation/analogy behind Key-policy Attribute-based Encryption?
CP... |
What is the motivation behind Key-policy Attribute-based Encryption? |
Knuth describes in "the art of computer programming part 2" an algorithm called "M" for mixing two streams of random numbers. This can be used to mix random number streams giving the assurance that the result is still random even if one (but only one) of the streams suddenly becomes predictable.
Now I have a situati... |
I'm doing Matasano's challenges and struggling with second part of 49th problem where I'm asked to do the length extension attack with CBC-MAC without IV manipulation. There is a hint that I can simulate iv somehow to do this but I don't understand. Can someone drop me some hint atleast? I did the part with forging the... |
I know there are way better and more tested encryption methods, but I was wondering if the following code could be use for symmetric encryption?
var text = "hello";
var password = "mypass";
var message = hash(text) + encrypt(text, password);
function encrypt(text, password){
var key = ... |
Could I use an hashing function for Symmetric encryption? |
I'm reading through the XEX mode spec, and I want to make sure I've understood the $\alpha^j$ step correctly:
$X = E_K(I) \oplus \alpha^j$
$C = E_K(M \oplus X) \oplus X$
where:
* $M$ is the plaintext message
* $I$ is the number of the sector
* $\alpha$ is the polynomial $2^n$ over the finite field $GF(2^{... |
If you add a truly random character into a truly random position of a word (uniformly chosen), you get "entropy of position" + "entropy of character" as addition to the entropy of the word. (Not exactly, it's a bit less). The entropy of character is the size of the possible characters. 64 possible characters would be $... |
I'm studying this white paper:
http://jessekornblum.com/publications/di09.pdf
The author says that using AES-CCM with the external key (highlighted in green at page 9, figure 4) and with the nonce at offset 0x3662B8 (highlighted in red, figure 5) you can decrypt the data at offset 0x3662D4.
I can't understand ho... |
How does AES-CCM work in BitLocker? |
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