instruction stringlengths 15 30k |
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Is there any easy way to crack a Beaufort cipher?
We have a Vigenère table, and are trying to guess the keyword.
Any easier way?
|
I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher.
I came across a website that describes the Chi-Square statistics in a rather simplistic manner and had also written some code to achieve my goals. However, the actual keyword does not seem... |
The Vigenère cipher can relatively easy be broken when the key size is small compared to the size of the message. One first finds the length of the key, and then uses frequency analysis to actually find the key.
1. How can one "add" something non-complicated to the Vigenère cipher to make it harder to break? Would i... |
Can I make a cipher (ex: Vigenère) harder to break? |
A theoretical question about the [Vigenère cipher][1]:
1. Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely recover the key?
2. What about if we know the key length? (I assume that we'll need plaintext with the same le... |
There is already a question asking "[Why initialize SHA1 with specific buffer?](http://crypto.stackexchange.com/questions/10829/why-initialize-sha1-with-specific-buffer/10857)" and my question follows on from this:
*Why are the initial states of hash functions often non-zero?*
For most, I have been able to find ... |
Why are the initial states of hashes functions (like SHA-1) often non-zero? |
Assume that we have a probability distribution $P(X,Y)$ for the joint probability of random variables $X$ and $Y$. Let $P(Y, Z)$ be analogous distribution for $Z$ and $Y$. Based on these we can define a joint probability distribution of $P(X,Y,Z)$.
Let, $P'(X,Y)$ and $P'(Y,Z)$ be analogously probability distribution... |
> Does anyone have a reliable source for this?
Well, you are asking about the definition of a CSPRNG, and whether this second criteria is a necessary part.
Well, it comes down the to exact definition of the term 'CSPRNG'.
If we define a CSPRNG as something that generates output which is indistinguishable fro... |
> Does anyone have a reliable source for this?
Well, you are asking about the definition of a CSPRNG, and whether this second criteria is a necessary part.
Well, it comes down the to exact definition of the term 'CSPRNG'.
If we define a CSPRNG as something that generates output which is indistinguishable fro... |
I'm trying to create a remote controller compatible with HiSec algorithm. It's so old that National (now Texas Instruments) discontinued NM95HS01/02 and docs are unavailable. Does anyone have the documentation that describe the algorithm code block? Maybe someone used them in an old project (al least 10 years ago..) an... |
I've read some papers about linear cryptanalysis. But since I am going to give a lecture about it I am looking for an example of breaking a system using this attack. Is there such an example available? |
I'm trying to create a remote controller compatible with HiSec algorithm. It's so old that National (now Texas Instruments) discontinued NM95HS01/02 and docs are unavailable. Does anyone have the documentation that describe the algorithm code block? Maybe someone used them in an old project (at least 10 years ago) and ... |
In the paper [Pairings for Cryptographers][1] we read about what the authors call a type 2 pairing in which we have a "pairing friendly curve $E$ over $\mathbb{F}_q$ with embedding degree $k>1$ and define $G_1$ to be the subgroup of $E(\mathbb{F}_q)$ of order $l$". We also define $G_2=\langle Q\rangle$ where $Q\in E(\m... |
Why is a simple hash into $G_2$ for (certain) pairing based crypto not possible? |
Are there any practical examples of breaking a system using linear attacks? |
I am working on Bent functions that are of interest in cryptography. I developed an algorithm that construct such functions. However, I need some tools to calculate boolean expression from the truth table. Is there such a application or applet available? (Actually I am interested in expressions without any NOTs). |
Are there any Truth Table to Boolean expression converters? |
Is it advisable to use AES CTR mode with the counter initialized to 0? How good is it in security terms? |
How good is using AES CTR mode with initial counter as 0? |
Suppose I have a file with random binary strings of the same length in each line.
If I'm computing the conditional entropy $H(Y|X)$ where $Y$ is the variable string of fixed length $l$ which is after $X$, and $X$ is the variable string of length $m$, and I find (lets say) $l=5$ and $m=10$ that the value of conditio... |
Best ways to estimate average bits of entropy in a byte stream.
I know there are different statistical tests out there (NIST, DieHarder, etc.), which all do different ways of analyzing entropy.
What I'm having a hard time finding is any particular literature which describes how to go from those tests to actual b... |
I know that this is not the best use case for RSA, but for a customer of mine I have to encode user data on the server in a way so that it can be decoded/downloaded by the customer through a "secure" webpage.
**Workflow**
Users can register on the page and leave some sensitive data (no credit card data, but age, ... |
My problem is to outsource an array of data and ask the prover to sort the data.
I am wonder if there is any working system out there that support interactive proof for the above computation? Or if none, any particular protocol that may be efficient enough and implementable for the problem of verifiable sorting? |
Any functioning system for interactive proof? |
I was wondering how we can get a secret sharing of $a+b$ from the sharing of secrets $a$ and $b$ themselves by using an XOR secret sharing scheme, where $a_1,...,a_n$ and $b_1,...,b_n$ are the shares for $a$ and $b$ respectively. Can anyone give me any suggestion? |
In [this paper][1] the last sentence of the first paragraph in the abstract states:
> We assume a (necessary) “leak-free” preprocessing stage.
But then later on in section 1.4 they say
> Another interesting open question is to construct a leakage- resilient
> MPC protocol without assuming any leak-free stage... |
Why do authors say conflicting things regarding leak-free stages in their paper? |
I am working on Intel AES-NI library and since the AES function is coded using low-level assembly instructions, I could not see in how IV or initial counter increases in CTR mode. But in general, how does IV or initial counter increase by itself for each 128-bit blocks(let's say we use AES_CTR_128)? Is it increases by ... |
How does the IV or initial counter increase internally for each block in AES CTR mode? |
In "[this paper][1]", the authors construct an encryption scheme that is supposed to be resilient to tampering and leaking (as opposed to just leaking).
Specifically this scheme:
![enter image description here][2]
If you look at the update procedure they simply multiply the current secret key g^s and multi... |
Why does the new encryption scheme proposed by authors stop and adversary from guessing the subspace of the secret key? |
Best ways to estimate average bits of entropy in a byte stream.
I know there are different statistical tests out there (NIST, Dieharder, etc), which all do different ways of analyzing entropy.
What I'm having a hard time finding is any particular literature which describes how to go from those tests to actual bi... |
I am working on Intel AES-NI library and since the AES function is coded using low-level assembly instructions. I could not see how the IV or initial counter increases in CTR mode. In general, how does the IV or initial counter increase by itself for each 128-bit block (let's say we use AES_CTR_128)? Does it increase b... |
In [this paper][1], the authors construct an encryption scheme that is supposed to be resilient to tampering and leaking (as opposed to just leaking).
Specifically this scheme:
![enter image description here][2]
If you look at the update procedure they simply multiply the current secret key $g^s$ and multipl... |
Why does the new encryption scheme proposed by authors stop an adversary from guessing the subspace of the secret key? |
I know that inventing one's one crypto always sucks, but the problem is that hand ciphers are usually
1. very insecure
2. very slow.
This is an attempt to make a relatively secure, keyable, and modular multi-round cipher by hand.
In each round of encryption the following two steps are done:
1. The text ... |
Are there any differences in operation between existing Diffie Hellman specifications, especially those within the RSA PKCS#3 and ANSI X9.42 standards?
I'm specifically interested in differences - if any - in operation and tests (on the input of the key agreement protocol, i.e. the public part of the other participa... |
Are there any differences in operation between existing Diffie-Hellman specifications, especially those within the [RSA PKCS#3](http://www.rsa.com/rsalabs/node.asp?id=2126) and [ANSI X9.42](http://tools.ietf.org/html/rfc2631) standards?
I'm specifically interested in differences - if any - in operation and tests (on... |
Are there any differences in operation between existing Diffie-Hellman specifications? |
Recently, I found a function that is performed on a sequence to return another sequence. All known algorithms for finding the input, given the output are of exponential complexity. I want to propose this function for encryption in a public key cryptosystem. What steps I am supposed to take? Actually I am a beginner in ... |
How to develop a public key cryptosystem based on a hard problem? |
I run into the following question:
Meet in the middle uses 2^56 memory.
Given the fact that the attacker has only 2^45 memory.
How can the attacker adjust the attack so even with this memory limit, it will still be more efficient than looking after all the existing keys?
I just can't figure this out :(
I guess ... |
I run into the following question:
Meet in the middle uses 2^56 memory.
Given the fact that the attacker has only 2^45 memory.
How can the attacker adjust the attack so even with this memory limit, it will still be more efficient than looking after all the existing keys?
I just can't figure this out :(
I guess ... |
Are there any differences in operation between existing Diffie-Hellman specifications, especially those within the [RSA PKCS#3](http://www.emc.com/emc-plus/rsa-labs/standards-initiatives/pkcs-3-diffie-hellman-key-agreement-standar.htm) and [ANSI X9.42](http://tools.ietf.org/html/rfc2631) standards?
I'm specifically ... |
Let's assume a ciphertext only attack, and compare it to Vigenere. Your scheme is on a quite similar level of security: It might be hard to break it without a computer, but with one it is probably done in seconds. Here's how:
First, your permutation is static and only depends on the number of rounds and the length o... |
I have been playing with base 26 LFSRs (i.e. using the alphabet) and noticed that the XOR operation for base 26 is just the tabula recta and so can be done very quickly. This made me wonder whether a base 26 LFSR (combined with a technique such as self shrinking) could be used as a PRNG that could be performed by hand ... |
Here's a couple of useful sources for definitions of CSPRNG or DRBGs (Deterministic Random Bit Generator).
Check out the NIST documents for CSPRNG ..
http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
http://csrc.nist.gov/publications/drafts/800-90/draft-sp800-90b.pdf
http://csrc.nist.gov/publica... |
Here's a couple of useful sources for definitions of CSPRNG or DRBGs (Deterministic Random Bit Generator).
Check out the NIST documents for CSPRNG ..
- http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
- http://csrc.nist.gov/publications/drafts/800-90/draft-sp800-90b.pdf
- http://csrc.nist.gov/p... |
Here's a couple of useful sources for definitions of CSPRNG or DRBGs (Deterministic Random Bit Generator).
Check out the NIST documents for CSPRNG:
- http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
- http://csrc.nist.gov/publications/drafts/800-90/draft-sp800-90b.pdf
- http://csrc.nist.gov/publ... |
Consider 4 people, $A$,$B$,$C$,$D$, & a secret $s\in\{0,1\}^k$. Construct a scheme
which enables the following subsets of people to retrieve the secret $\{A,B\}$, $\{A,C\}$, $\{B,C,D\}$.
I know that we can use Shamir's secret sharing scheme to do so, and A should be allocated more shares than the others, but how do... |
In the comments of [this question](http://crypto.stackexchange.com/questions/10348/hmac-construction-based-on-the-combination-of-two-hash-functions), Ricky Demer proposes a function $HMAX$ to combine two hash functions $H_1$ and $H_2$ while preserving the PRF properties of each of them (the OP talked about retaining Co... |
How does use of HMAC affect hash function combiners? |
How are IVs used in association with RSA Encryption?
Can some one explain why we use them in this RSA context?
Thanks in advance. |
In the comments of [this question](http://crypto.stackexchange.com/questions/10348/hmac-construction-based-on-the-combination-of-two-hash-functions), Ricky Demer proposes a function $HMAX$ to combine two $HMAC$s based on different hash functions:
$HMAX_{H0,H1}(⟨k_0,k_1⟩,m) = HMAC_{H0}(k_0,m) \oplus HMAC_{H1}(k_1,m)$... |
I've discovered that a client has [SEED](http://en.wikipedia.org/wiki/SEED_(cipher)) enabled in their SSL ciphers, and would like to know a bit more about it from a security perspective. The Wikipedia article doesn't mention any flaws, yet I've found two papers that demonstrate attacks - a differential fault analysis, ... |
I know how to calculate the entropy of a key that relates to its selection process. For example if the key space is 1000, entropy of a randomly chosen key is 1000. Suppose now you have two keys X and Y. The finale key Z is a concatenation of X and Y. There are two ways to combine. One is to use XOR and other way is to ... |
If I have the unencrypted text and the encrypted text, can I calculate the key? It seems logical based on my limited knowledge of encryption that I should be able to... but it also seems like too obvious of a vulnerability for it to be possible.
Could someone explain how encryption schemes prevent against this type... |
If I have the unencrypted text and the encrypted text, can I calculate the key? |
Computing the HMAC-SHA1, HMAC-SHA2 etc. is quite clear to me.
However why/how is this HMAC value used in conjunction with AES for encyrption/decryption and Signing/Verifying for different keysizes like AES 128,196,256 etc?
Where are these used?
Is the calculated MAC encrypted using AES? What is the purpose?
How a... |
> Is the calculated MAC encrypted using AES? What is the purpose? How
> about signing and verifying? How does AEs Play a role here? Is the
> case here that the encrypted AES is HMACed for signing and the HMAC is
> verified
No, the MAC is not encrypted per se, however, it is calculated in conjunction with a key (i... |
> Is the calculated MAC encrypted using AES? What is the purpose? How
> about signing and verifying? How does AEs Play a role here? Is the
> case here that the encrypted AES is HMACed for signing and the HMAC is
> verified
No, the MAC is not encrypted per se, however, it is calculated in conjunction with a key (i... |
Meet in the middle on 2DES uses $2^{56}$ memory.
Given the fact that the attacker has only $2^{45}$ memory.
How can the attacker adjust the attack so even with this memory limit, it will still be more efficient than looking after all the existing keys?
I guess you can separate this to a few lookups - a few tables ... |
I understand how to compute HMAC-SHA1, HMAC-SHA2 etcetera.
Please explain why/how is the resulting HMAC value is used in conjunction with AES for encryption/decryption and signing/verifying.
In particular:
0. How does HMAC interact with AES for key sizes (AES-128, AES-196 and AES-256)?
1. Is the calculate... |
Consider 4 people, $A$,$B$,$C$,$D$, & a secret $s\in\{0,1\}^k$. Construct a scheme
which enables the following subsets of people to retrieve the secret $\{A,B\}$, $\{A,C\}$, $\{B,C,D\}$.
I know that we can use Shamir's secret sharing scheme to do so, and A should be allocated more shares than the others. But how do... |
I'll answer your question in order of appearance:
1. HMAC can be used with any key size (as the key is basically used as input for the underlying hash function). If the key size is too small then the security of the HMAC is of affected. In general, the key size should be at least the output size of the hash algori... |
I know how to calculate the entropy of a key that relates to its selection process. For example if the key space is 1000, entropy of a randomly chosen key is 1000. Suppose now you have two keys $X$ and $Y$. The finale key $Z$ is a concatenation of $X$ and $Y$. There are two ways to combine. One is to use XOR and other ... |
My banksite uses this style of crypto ssl_rsa_with_rc4_128_md5 and am not familiar with cryptoghraphy I just ask you
Is it secure?? |
Is it this cipher secure? |
Cryptographic hash functions normally take as input a bitstring.
I am looking for a hash function that takes as input a finite set of values. In other words, given $S \subset \{0,1\}^*$, I want to compute $H(S)$, a hash of $S$. Also, I would like this function to be chosen so that given the hashes $H(S),H(T)$ of t... |
Cryptographic hash functions normally take as input a bitstring.
I am looking for a hash function that takes as input a finite multiset of values. In other words, given $S \subset \{0,1\}^*$, I want to compute $H(S)$, a hash of $S$. Also, I would like this function to be chosen so that given the hashes $H(S),H(T)$... |
In Elgamal, the generator g is always quadratic residue modulo p where p is a safe prime?
and inverse of g can be also generator? Can I prove it?
I can't come up with it at all.
|
In Elgamal, the generator g is always quadratic residue modulo p where p is a safe prime? and inverse of g can be also generator? |
How is digital signature different from a message authentication code (MAC)? |
In Elgamal, the generator g is always quadratic non- residue modulo p where p is a safe prime?
and inverse of g can be also generator? Can I prove it?
I can't come up with it at all.
|
In Elgamal, the generator g is always quadratic non-residue modulo p where p is a safe prime? and inverse of g can be also generator? |
In Elgamal, the generator $g$ is always quadratic non-residue modulo $p$, where $p$ is a safe prime and the inverse of $g$ can also be generator?
Can I prove it? I can't come up with it at all.
|
In Elgamal, the generator g is always quadratic non-residue modulo p where p is a safe prime and inverse of g can be also generator? |
My banksite uses this style of crypto: "ssl_rsa_with_rc4_128_md5".
I am not familiar with cryptoghraphy — is that secure? |
Is it this cipher (ssl_rsa_with_rc4_128_md5) secure? |
I'll probably get shot for asking this, but I've got some kids (aged 8-10) in my neighbourhood that I've been showing/teaching the simple pen-and-paper Cesar cipher and they're successfully playing with it for more than a week now.
Silly me thought it would be great to now show them the concept of message authentica... |
How would you encrypt-then-MAC using a pen-and-paper Cesar cipher? |
I'll probably get shot for asking this, but I've got some kids (aged 8-10) in my neighbourhood that I've been showing/teaching the simple pen-and-paper Cesar cipher and they're successfully playing with it for more than a week now.
Silly me thought it would be great to now show them the concept of message authentica... |
How would you encrypt-then-MAC when using pen-and-paper and a Cesar cipher? |
My banksite uses "ssl_rsa_with_rc4_128_md5".
Are there known weaknesses that have a practical impact?
|
Does ssl_rsa_with_rc4_128_md5 have known weaknesses? |
I'll probably get shot for asking this, but I've got some kids (aged 8-10) in my neighbourhood that I've been showing/teaching the simple pen-and-paper Caesar cipher and they're successfully playing with it for more than a week now.
Silly me thought it would be great to now show them the concept of message authentic... |
How would you encrypt-then-MAC when using pen-and-paper and a Caesar cipher? |
For a start, I 've got a question regarding the Public key encryption.
I know the public key encryption overcomes the Key distribution issue with the symmetric encryption and that in the case of communication between 2 parties, there is a total of 4 keys (each party has a public and a private key )
But here's what'... |
The part you're missing here is that Public Key encryption is **asymmetric** - that is, data can only be _encrypted_ with the public key, and can only be _decrypted_ with the private key. Public key encryption systems are created in such a way that the _encryption_ is (mostly) irreversible, but there is a mathematical ... |
I'm having hard time with the implementation of the S-Boxes by Osvik found in this paper: [Speeding up Serpent][1]. At the end of the paper, all the s-boxes are given and then, I just implement them. Here's my implementation of $S_0$ as an example :
UInt32Vector Serpent::S0(const UInt32Vector &Y)
{
... |
In the [FFX spec][1], there is a note about using CMAC as the round function.
> Security notes. The round function F is constructed in such a way that the set of inputs on
which the CBC-MAC is invoked is prefix-free. (A set of strings is prefix-free if for any distinct x, y
in the set, x is not a prefix of y.) The... |
Why does CBC-MAC need prefix-free inputs to be a good PRF? |
What is best to use (for message integrity) between:
1 - AES(Data) + HMAC(Data)
2 - AES(Data + HMAC(Data))
3 - AES(Data + Hash(Data))
And why?
Thanks |
What is best to use (for message integrity) between…
1. AES(Data) + HMAC(Data)
2. AES(Data + HMAC(Data))
3. AES(Data + Hash(Data))
…and why? |
I'm writing some software that requires the use of a CSPRNG with javascript for use in the browser and I'm wondering what libraries are available. Crypto-js doesn't seem to have a CSPRNG I can directly call (unless I missed it?). I've looked through the Stanford crypto js library, but I'm uncertain how much analysis th... |
Why does WPA-PSK not use Diffie-Hellman key exchange? |
It seems to me an exhaustive search would simply try to use all the possible bit combinations of a key, while factorization is some mathematical formula for determining the key? When discussing the NSA's cryptography "breakthroughs" some articles discuss factorization as the contributing factor. However, others go furt... |
What is the difference between exhaustive search and factorization in relationship to determining a key? |
First up: I would try to avoid doing any cryptography using javascript… but that's just my personal opinion. One of the reasons is that Javascript code can't ask, "am I really dealing with a random number generator, or with something provided by an attacker?"
Anyway… you could skip the libraries and take a look at ... |
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