instruction stringlengths 15 30k |
|---|
I am aware that there are concerns if $p$ and $q$ are close i.e. $\Delta=|p-q|$ can't be too small. But I would like to know if there are any known attacks for cases where $p$ and $q$ take on different bit-sizes. (Don't mention extreme cases where the bit-size is close to the modulus.)
Are there vulnerabilities? Can... |
I've implemented LibTomCrypt's version of fortuna and am wondering about the pool resetting after a reseed. In fortuna.c in libtomcrypt we have the following (which is that part that adds the entropy from the pools into the key),
for (x = 0; x < LTC_FORTUNA_POOLS; x++) {
if (x == 0 || ((prng->fortuna.rese... |
Why are Fortuna entropy pools reset after a reseed? |
Since Blum-Micali is cryptographically secure, you know that there won't be a short cycle (not one short enough to detect in polynomial time), because a short cycle would violate cryptographic security. Therefore, you don't need to worry about this. It's not worth your time worrying about it: it's very unlikely you'l... |
How could Fully Homomorphic Encryption support power operations? |
I have a hypothetical encryption scheme where somebody uses the one-time pad in CBC mode. That is, the block cipher is E(k, m) :=k⊕m, and that block cipher is used in CBC mode.
Now, I am assuming that a message m=m1|| m2 || m3 ||m4 is used for encryption.
Now, How to compute m3⊕m4 from the resulting ciphertext. (... |
I have a hypothetical encryption scheme where somebody uses the one-time pad in CBC mode. That is, the block cipher is $E(k, m) :=k⊕m$, and that block cipher is used in CBC mode.
Now, I am assuming that a message $m=m_1||m_2||m_3||m_4$ is used for encryption.
How to compute $m_3⊕m_4$ from the resulting ciphertext... |
Remark: in One Time Pad the pad is used once, thus this is not OTP, since here $k$ is reused.
Hint for part 1: Write the relations between $k$, the message blocks $m_i$, the ciphertext blocks $\small C_i$ with the convention $\small\text{IV}=\small C_0$. Then, find equations that allow computing the desired $m_3⊕m_4... |
What do you think of converting SpookyHash into semi-secure 192bit hash function by this way:
- increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * 12byte = 768bit state (so that 256bit are used for "oracle")
- run more EndPartial rounds in End, to produce more ent... |
We do compression in PGP.
Does this step increase/decrease or either have any effect regarding the ***authentication*** of a message? |
What do you think of converting SpookyHash into semi-secure 192bit hash function by this way:
- increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * 12byte = 768bit state (so that 256bit are used for "oracle")
- run more EndPartial rounds in End, to produce more ent... |
As stated in the comments, [dev/random](http://en.wikipedia.org/wiki//dev/random) already produces cryptographically secure random bytes which are perfectly adequate for use in encryption keys. Running these bytes through another CSPRNG is completely redundant.
> As far as I've understood, one of the options to cr... |
In his paper "Alternating Step Generator Controlled by de Bruijn Sequence" C. Gunther states on page three that "it is easy to convert an m-sequence (maximal length LFSR sequence) into a de Bruijn sequence". Unfortunately he gives no method for doing this in the paper and I have been unable to find such a method in my ... |
I'm trying to find a special kind of Digital Signature Scheme.
Suppose I have a signature: s=sign(sk,m), where sk is a secret key and m is a message.
Is there a signature scheme that allows one to have sign(sk,m) = s = sign(sk',m), where sk' is another secret key that has a secret relation to sk, and maps to anot... |
Is there a malleable pubkey digital signature scheme? |
I want to know what values are appropriate for the **public exponent** and **certainty** when generating an RSA Key (for example using Bouncy Castle RSAKeyGenerationParameters function).
What is the significance of the the **string to key count (s2kcount)** which appears to be optional input for the BcPBESecretKeyE... |
###Q1: Why are these tests stroked out?
These tests are stroked out on pages 57-58 of the [current FIPS 140-2](http://csrc.nist.gov/publications/fips/fips140-2/fips1402.pdf) because they are no longer part of the current FIPS 140-2 standard, since Change Notice 2 of 2002 December third, where these pages b... |
I'm trying to find a special kind of Digital Signature Scheme.
Suppose I have a signature: s=sign(sk,m), where sk is a secret key and m is a message.
Is there a signature scheme that allows one to have sign(sk,m) = s = sign(sk',m), where sk' is another secret key that has a secret relation to sk, and maps to anot... |
**Short answer: public exponent $65537$, certainty $5$.** <sub><sup>Terms and Conditions May Apply.</sup></sub>
---
Whenever one wants to know " _what values are appropriate_ ", there's the problem of defining _appropriate_: is there some normative context, e.g. [FIPS 186-4][1]? I'll assume that refe... |
Short answer: **public exponent $65537$, certainty $5$.** <sub><sup>Terms and Conditions May Apply.</sup></sub>
I have no clues about **string to key count**.
---
Whenever one wants to know " _what values are appropriate_ ", there's the problem of defining _appropriate_: is there some normative context... |
Short answer: **public exponent $65537$, certainty $5$.** <sub><sup>Terms and Conditions May Apply.</sup></sub>
I have no clues about **string to key count**.
---
Whenever one wants to know " _what values are appropriate_ ", there's the problem of defining _appropriate_: is there some normative context... |
What is your opinion on this scheme:
1)get IV from CSPRNG
2)set 3 encryption keys k1,k2,k3 (3*key_lenght) (KDF/PBKDF)
Use 3 ciphers in CTR mode like this:
The initial IV is encrypted using cipher1 with key k1 , then the iv is incremented and encrypted by using cipher 2 that uses the second key and so on, the outp... |
What is your opinion on this scheme:
1)get IV from CSPRNG
2)set 3 encryption keys k1,k2,k3 (3*key_lenght) (KDF/PBKDF)
3)Use 3 ciphers in CTR mode like this:
The initial IV is encrypted using cipher1 with key k1 , then the iv is incremented and encrypted by using cipher 2 that uses the second key and so on, ... |
i want to encrypt transparently using Rijndael. So this is, what I thought of and I would like to have an opinion from "Experts" whether this will harm encryption strenght.<br />
<li>I am using chunks of 1MB and give them a GUID as filename. </li>
<li>These chunks are then first compresses using DEFLATE to minimize a... |
IV = Filename XOR CipherKey? |
Chaocipher was invented by JFByrne in 1919.
The algorithm was recently revealed -- see http://www.mountainvistasoft.com/chaocipher/ActualChaocipher/Chaocipher-Revealed-Algorithm.pdf
While a known plaintext attack successfully finds the keys, nobody has been able to put forward a general solution to this cipher. ... |
Is Chaocipher a secure cipher? |
What do you think of converting SpookyHash into semi-secure 192bit hash function by this way:
- increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * 12byte = 768bit state (so that 256bit are used for "oracle")
- run more EndPartial rounds in End, to produce more ent... |
What do you think of converting SpookyHash into semi-secure 192bit hash function by this way:
- increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * 12byte = 768bit state (so that 256bit are used for "oracle")
- run more EndPartial rounds in End, to produce more ent... |
Chaocipher was invented by John F. Byrne in 1919.
The algorithm was recently revealed -- see Moshe Rubin's [_Chaocipher Revealed, the Algorithm_][1]
While a known plaintext attack successfully finds the keys, nobody has been able to put forward a general solution to this cipher. Is that possible?
[1]: htt... |
Is Chaocipher a secure cipher under ciphertext-only attack? |
What do you think of converting SpookyHash into semi-secure 192bit hash function by this way:
- increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * 12byte = 768bit state (so that 256bit are used for "oracle")
- run more EndPartial rounds in End, to produce more ent... |
Short answer: **public exponent $65537$, certainty $5$.** <sub><sup>Terms and Conditions May Apply.</sup></sub>
I have no clues about **string to key count**.
---
Whenever one wants to know " _what values are appropriate_ ", there's the problem of defining _appropriate_: is there some normative context... |
Short answer: **public exponent $65537$, certainty $5$.** <sub><sup>Terms and Conditions May Apply.</sup></sub>
I have no clues about **string to key count**.
---
Whenever one wants to know " _what values are appropriate_ ", there's the problem of defining _appropriate_: is there some normative context... |
Short answer: **public exponent $65537$, certainty $5$.** <sub><sup>Terms and Conditions May Apply.</sup></sub>
I have no clues about **string to key count**.
---
Whenever one wants to know " _what values are appropriate_ ", there's the problem of defining _appropriate_: is there some normative context... |
In his paper [_Alternating Step Generator Controlled by de Bruijn Sequence_][1], C.G. Günther states on page three that
> a de Bruijn sequence (..) can easily be obtained from an m-sequence (maximal length LFSR sequence)
Unfortunately he gives no method for doing this in the paper, and I have been unable to find ... |
i want to encrypt transparently using Rijndael. So this is, what I thought of and I would like to have an opinion from "Experts" whether this will harm encryption strenght.<br />
<li>I am using chunks of 1MB and give them a GUID as filename. <br>
**edit**: The 1MB chunks are just out of performance reasons. Imagine ... |
(Please note: this is purely a thought experiment and not intended for any real-world usage!) I came up with a simple function to map the numbers in the space from zero to `"fff"` (4095, call that `ChunkSize`) to 512-bit hashes. The function acts such that for any `(a, b)` pair `a < b` if and only if `OPF(a) < OPF(b)`.... |
What's wrong with this "order-preserving hash" function? |
(Please note: this is purely a thought experiment and not intended for any real-world usage!) I came up with a simple function to map the numbers in the space from zero to `"fff"` (4095, call that `ChunkSize`) to 512-bit hashes. The function acts such that for any `(a, b)` pair `a < b` if and only if `OPF(a) < OPF(b)`.... |
<sub>Please note: this is purely a thought experiment and not intended for any real-world usage!</sub>
I came up with a simple function $\mathrm{OPF}$ to map the integers $[0,C)$ (where $C$ is the "ChunkSize") to $512$-bit hashes such that for any $(a, b)$
$$a < b\iff \mathrm{OPF}(a) < \mathrm{OPF}(b)$$
I'm wonder... |
What's wrong with this keyed order-preserving hash function? |
<sub>Please note: this is purely a thought experiment and not intended for any real-world usage!</sub>
I came up with a simple function $\mathrm{OPF}$ to map the integers $[0,C)$ (where $C$ is the "ChunkSize") to $512$-bit hashes such that for any $(a, b)$
$$a < b\iff \mathrm{OPF}(a) < \mathrm{OPF}(b)$$
I'm wonder... |
What's wrong with this "order-preserving MAC" function? |
<sub>Please note: this is purely a thought experiment and not intended for any real-world usage!</sub>
I came up with a simple function $\mathrm{OPF}$ to map the integers $[0,C)$ (where $C$ is the "ChunkSize") to $512$-bit hashes such that for any $(a, b)$
$$a < b\iff \mathrm{OPF}(a) < \mathrm{OPF}(b)$$
I'm wonder... |
i want to encrypt transparently using Rijndael. So this is, what I thought of and I would like to have an opinion from "Experts" whether this will harm encryption strenght.<br />
<li>I am using chunks of 1MB and give them a GUID as filename. <br>
**edit**: The 1MB chunks are just out of performance reasons. Imagine ... |
i want to encrypt transparently using Rijndael. So this is, what I thought of and I would like to have an opinion from "Experts" whether this will harm encryption strenght.<br />
<li>I am using chunks of 1MB and give them a GUID as filename. <br>
**edit**: The 1MB chunks are just out of performance reasons. Imagine ... |
Or in other words: Why is it considered a bad idea, to create an IV from f.e. a filename XOR CipherKey, when you never store the IV?
The question came up here: http://crypto.stackexchange.com/questions/15455/iv-filename-xor-cipherkey
I know, that XOR is a no-go, when you are using ciphers, because, XOR is bidirecti... |
Is it possible to deduce the IV from Rijndael ciphered data, without knowing the key? |
Does anyone know about Locally Decodable Codes (LDCs)? It seems the private information retrieval schemes that based on LDCs are computationally efficent (answer a query without processing the whole database). Why LDCs receives little attention in cryptographic world? |
Is it possible to deduce the IV from Rijndael CBC ciphered data, without knowing the key? |
The question came up [here](http://crypto.stackexchange.com/questions/15455/iv-filename-xor-cipherkey), which left me thinking:
**Why is it considered a bad idea to create an IV by, for example, `filename`$\oplus$`Key`, if you never store the IV?**
I know, that XOR is a no-go, when you are using ciphers, because,... |
Is it possible to deduce the IV from CBC ciphered data, without knowing the key? |
Issues with the question first:
1. Security is not something you can duct tape on to anything you want after the fact.
2. You can never increase information entropy by processing data. It can be kept constant or decreased depending on whether you are doing a lossless or lossy tranformation.
3. HASH("secret"+"publ... |
Issues with the question first:
1. Security is not something you can duct tape on to anything you want after the fact.
2. You can never increase information entropy by processing data. It can be kept constant or decreased depending on whether you are doing a lossless or lossy tranformation.
3. HASH("secret"+"publ... |
Can anyone comment if the stream cipher described here (first post) is safe?
https://nextcoin.org/index.php?topic=727.0
The claim is that it is unbreakable. It has three parts:
Seed generation (Curve25519 shared secret)
Key generation (sequence of SHA256 operations)
Xoring (Unbreakable if some conditions... |
Some brief thoughts:
**Shared secret Generation:**
$$s=E_a(B)=E_b(A)$$
The shared secret is generated by encrypting the other users public key with your private key. I'm not quite sure on the specification of curve25519 (definitely something I should read up on sometime soon), but I don't *think* the properties us... |
Devise a scheme so that a message M can be shared among X, Y and Z in such a say that the only way of recovering the message is when X is present with either Y or Z. When X isn't present or each is alone, they will not be able to recover the shared secret.
Additionally, generalize the above to devise a scheme so tha... |
Here is the scenario:
- "SECRET" is a secret key that is kept private and never revealed to users
- An application allows users to enter in any "VALUE"
- The application creates an HMAC-SHA2-256 "HASH" from VALUE using SECRET as the key
- HASH is displayed to the user
"CONTROL" (comparison) scenario:... |
Does displaying HMAC hashes of user inputs compromise the private key? |
Here is the scenario:
- "SECRET" is a secret key that is kept private and never revealed to users
- An application allows users to enter in any "VALUE" (within various open-ended limits such as numeric > 50, max length 20, etc... depending on the field)
- The application creates an HMAC-SHA2-256 "HASH" from... |
Here is the scenario:
- "SECRET" is a secret key that is kept private and never revealed to users and only used in this one application.
- The application allows users to enter in any "VALUE" (within various open-ended limits such as numeric > 50, max length 20, etc... depending on the field)
- The applicat... |
Here is the scenario:
- "SECRET" is a secret key that is kept private and only used in this one application.
- The application allows users to enter in any "VALUE" (within various open-ended limits such as numeric > 50, max length 20, etc... depending on the field)
- The application creates an HMAC-SHA2-256... |
Does displaying HMAC hashes of user inputs compromise the HMAC validation? |
Here is the scenario:
- "SECRET" is a secret key that is kept private and only used in this one application.
- The application allows users to enter in any "VALUE" (within various open-ended limits such as numeric > 50, max length 20, etc... depending on the field)
- The application creates an HMAC-SHA2-256... |
Let's say there are 100 choices (which are publicly known), each represented as a different string, and today you have to choose one of them. You need not reveal what that choice is right now, though. One thing you could do is take your choice, append a bunch of entropy at the end, and publish your signature of the res... |
Zero-knowledge proof for committing a choice? |
If I hash a keyword with SHA-512 and then feed the output as the key for the next round ....and keep repeating this process, will I gather a stream of random numbers? |
Will repeated rounds of SHA-512 provide random numbers? |
Some brief thoughts:
**Shared secret Generation:**
$$s=E_a(B)=E_b(A)$$
The shared secret is generated by encrypting the other users public key with your private key. This is effectively an ECDH step, which is very reasonable, and one of the key aims of C25519$^{[1]}$.
**Key Generation:**
$$s_0=\mathrm{SHA256}... |
> Does allowing users to test VALUEs increase the likelihood that SECRET will be broken or illegal hashed values generated, relative to the CONTROL scenario?
By definition a cryptographic [Message Authentication Code](http://en.wikipedia.org/wiki/Message_authentication_code) such as HMAC is secure only if _resists ... |
This question was asked in comments on my answer to [should we sign then encrypt or encrypt then sign](http://crypto.stackexchange.com/q/202/46). I think posing the question as a separate entity is best, so:
The general advice for [applying MACs](http://crypto.stackexchange.com/q/202/46) seems to be that we should e... |
Why do we encrypt-then mac but sign-then-encrypt? |
Okay. So first up, let's eliminate encrypt-then-sign. Why is this a problem? The idea behind a signature is to prove that a message came from me even in the presence of malicious actors. If a malicious actor changes the ciphertext under the signature, clearly this invalidates the signature as per expectations, however,... |
Can anyone comment if the stream cipher described here (first post) is safe?
https://nextcoin.org/index.php?topic=727.0
The claim is that it is unbreakable. It has three parts:
Seed generation (Curve25519 shared secret)
Key generation (sequence of SHA256 operations)
Xoring (Unbreakable if some conditions r... |
The question came up [here](http://crypto.stackexchange.com/questions/15455/iv-filename-xor-cipherkey), which left me thinking:
**Is it possible to deduce the IV from CBC ciphered data, without knowing the key?
And if not, why is it considered a bad idea to create an IV by, for example, `filename`$\oplus$`Key`, if ... |
Some brief thoughts:
**Shared secret Generation:**
$$s=E_a(B)=E_b(A)$$
The shared secret is generated by encrypting the other users public key with your private key. This is effectively an ECDH step, which is very reasonable, and one of the key aims of C25519$^{[1]}$.
**Key Generation:**
$$s_0=\mathrm{SHA256}... |
Can anyone comment if the stream cipher described here (first post) is safe?
https://nextcoin.org/index.php?topic=727.0
The claim is that it is unbreakable. It has three parts:
1. Seed generation (Curve25519 shared secret)
2. Key generation (sequence of SHA256 operations)
3. XORing (Unbreakable if some con... |
Can anyone comment if the stream cipher described [here](https://nextcoin.org/index.php?topic=727.0) is safe? The author claims it to be unbreakable, but does not provide any evidence or proof to support this. For completeness, I have reproduced the algorithm below.
**Encryption routine (Alice$\to$Bob)**
1. C... |
Key space is the set of all possible keys that can be used to generate a key.we using the number of valid key to describe it.
Q: I've given a hill cipher of block size k over alphabet of size p, where p is prime, how many keys there (valid key)?
since the hill cipher key is a k x k matrix, all the elements gettin... |
Key space is the set of all possible keys that can be used to generate a key.we using the number of valid key to describe it.
Q: I've given a hill cipher of block size k over alphabet of size p, where p is prime, how many keys there (valid key)?
since the hill cipher key is a k x k matrix, all the elements gettin... |
The multiplicatively homomorphic variant of RSA is not [semantically secure][1]. This is a major disadvantage. ElGamal is a semantically secure, multiplicativey homomorphic cipher. Paillier is a semantically secure, additively homomorphic cipher.
As described by tylo, all homomorphic ciphers are malleable by definit... |
I recently came across a [library](http://www.outsystems.com/forums/discussion/10565/documentation/) that promises to do deterministic encryption with the following scheme:
> AES with 256 bit key in CBC mode with PKCS7 padding and Synthetic Initialization vector taken from the first 16 bytes of the HMACSHA256 mac of t... |
My previous answer was about the IOSR-JECE paper, since you posted the link to JACN paper.
That paper is considerably better written; it doesn't have any obvious meaningless sentences.
Unfortunately, the increased clarity makes it more obvious that *their system is insecure as specified*.
I'll abstract out the... |
My previous answer was about the IOSR-JECE paper, since you posted the link to JACN paper, I went through that one as well.
That paper is considerably better written; it doesn't have any obvious meaningless sentences.
Unfortunately, the increased clarity makes it more obvious that *their system is insecure as spe... |
My previous answer was about the IOSR-JECE paper, since you posted the link to JACN paper, I went through that one as well.
That paper is considerably better written; it doesn't have any obvious meaningless sentences.
Unfortunately, the increased clarity makes it more obvious that *their system is insecure as spe... |
I look for one-pass deniable authentication protocol with a short message payload for my project and find a solution:
*Wei-Bin Lee, Chia Chun Wu, and Woei-Jiunn Tsaur. "A novel deniable authentication protocol using generalized ElGamal signature scheme." Inf. Sci.-177(6):1376-1381 (2007)*
Unfortunately later ... |
Reliability of a single-pass deniable authentication protocol? |
I am currently trying to implement a AES-256 cipher according to this sepcificaciton:
http://techheap.packetizer.com/cryptography/encryption/spec.v36.pdf
As well as on Wikipedia and in the document these offsets for the shift-rows operation are given (depending on the key size):
Row 128 192 256
1 0... |
Actually, the document talks about Rijndael, not AES.
Aren't Rijndael and AES that same? Well, not precisely; Rijndael is specified with a set of parameters that AES does not support; how example, how it works with different block sizes. AES is defined only with a block size of 128; Rijndael supports a set of diff... |
I have a lead about the origin and meaning of $h$, based on the [abstract of an ITNG 2008 paper][1] (which is reference [6] of the [JACN paper][2]):
> In this paper, we propose an efficient RSA public key encryption
> scheme, which is improved version of original RSA scheme. The proposed
> RSA encryption scheme is... |
I have a lead about the origin and meaning of $h$, based on the [abstract of an ITNG 2008 paper][1] (which is reference [6] of the [JACN paper][2]):
> In this paper, we propose an efficient RSA public key encryption
> scheme, which is improved version of original RSA scheme. The proposed
> RSA encryption scheme is... |
I'm studying universal hash functions and have been reading several papers but now i'm focusing on Wegman and Carters original paper from 1979 (Universal classes of hash functions) and the *H1* class.
1. Choose a prime *p* that is *p* >= *a*
2. Let *g* be residue modulus *b* (*g*(x) = x mod *b*)
3. Then the *H1... |
Is this a correct understanding of Universal Hash Functions? |
I'm studying universal hash functions and have been reading several papers but now i'm focusing on Wegman and Carters original paper from 1979 (Universal classes of hash functions) and the *H1* class.
1. Choose a prime $p$ that is $p >= a$
2. Let $g$ be residue modulus $b$ ($g(x) = x \pmod b$)
3. Then the $H1$ ... |
Where can I find source or an example of Knapsack Cryptosystem cracks/attacks? |
An example of Knapsack Cryptosystem cracks/attacks? |
We have a multiplicative cyclic group G which is a subgroup of (Z/nZ)∗. There are two parties, Alice and Bob:
Alice knows: a,b and x such that a^(x*x) = b
Bob knows: a,b
What's the easiest non-interactive way Alice can prove to Bob the knowledge of x without leaking x? |
Is there a simple zero knowledge proof for a discrete log squared? |
why is it recommended to write cryptography programs ,for example crypt-analysis projects with python programming language?
what is the advantages of python? why not use c or any other language?
|
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