instruction stringlengths 15 30k |
|---|
How fast can a wrong decryption key be detected using ECC? |
If we assume that the support for an irreducible binary Goppa code $\gamma_1, ..., \gamma_n$ is publicly known, when is it possible to efficiently decode the code? I know it's possible if one knows the generator polynomial $g(x)$, and also, if one can obtain a parity check matrix $H$ of the form $XYZ$, where
$ X = \... |
I am signing a short message using the base64 of an HMAC, like this (python):
import hashlib
import hmac
import base64
raw = hmac.new("key", msg="secret", digestmod=hashlib.sha1).digest()
base64.urlsafe_b64encode(raw)
That last line returns `'ux5F7Ye-rpwvysbzUBLu-wGaYXA='`, which I use... |
Is there a preferred way on how to transmit the initiliazation vector with witch AES encryption was made? I could imagine that, if the encrypted data is stored to a file, the IV is preppended at the file's beginning before the actual encrypted data (or somehting similar).
Is there such a convention? |
If I have received an AES encrypted message, and if I do know they key with which it was encrypted, do I also need to know the *mode of operation* with which it was encrypted in order to decrypt it? My understanding is that this is indeed the case.
If so, how is the mode of operation transmitted along with the encry... |
Do I need to know the "mode of operation" to decrypt a message encrypted with a block cipher? |
If I have received an AES encrypted message, and if I do know the key with which it was encrypted, do I also need to know the *mode of operation* with which it was encrypted in order to decrypt it? My understanding is that this is indeed the case.
If so, how is the mode of operation transmitted along with the encryp... |
I'm taking a cryptography introduction course, and we're covering the definition of a secure PRF.
I understand the test goes as follows: A challenger picks a function $f$ such that
$f \leftarrow \left\{
\begin{array}{lr}
b=1: k\leftarrow K, f\leftarrow \left(k,\cdot \right ) \\
b=0: Funs \le... |
Distinguishing $H^2$ from a random oracle (essentially an ideal hash) is much cheaper that it should, namely $2^{64}$ for $\operatorname{SHA-256d}$. This doesn't lead to any practical attacks, but it hurts security proofs relying on indistinguishably. It is easy to avoid this problem by using distinct prefixes for the ... |
I was reading RFC 2898 and something is not clear to me. When you use PBKDF2 with sha256 and i want a derived key with length 32 bytes (the same length as my hash functie), your derived key only exists out 1 block (l) of size (hLen: 32bytes).
This seems trivially, but i want to be very sure! Is this correct? |
I was reading [RFC 2898][1] and something is not clear to me. When I use PBKDF2 with SHA-256 and I want a derived key with length 32 bytes (the same length as my hash function output), your derived key only exists out 1 block (`l = 1`) of size `hLen = 32` bytes.
This seems trivially, but i want to be very sure! Is ... |
How do I generate decryption keys for the IDEA algorithm from the 128 bit key? |
I was thinking about this today and thought I should ask. I think I understand IV's enough to say that they are basically the same thing as Salts when talking about hashes. They are there to improve randomness between messages. If the IV is simple appended, or prepended to the plain text, why does AES need to know the ... |
Does the IV need to be known by AES (CBC mode)? |
Distinguishing $H^2$ from a random oracle (essentially an ideal hash) is much cheaper that it should, namely $2^{64}$ for $\operatorname{SHA-256d}$. This doesn't lead to any practical attacks, but it hurts security proofs relying on indistinguishably. It is easy to avoid this problem by using distinct prefixes for the ... |
There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used in the first round, and this goes on and on until OFB is done.
So the output of the block cipher is deterministic a... |
There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used in the first round, and this goes on and on until OFB is done.
So the output of the block cipher is deterministic a... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to explain, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To Hash... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used in the first round, and this goes on and on until OFB is done.
So the output of the block cipher is deterministic a... |
There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used in the first round, and this goes on and on until OFB is done.
So the output of the block cipher is deterministic a... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
Given an entrophy of 1.5 bits per character, how long does a passphrase have the be to guarantee a key strength of a 128 bit random key?
Assuming an alphabet of 26, one character takes log2(26)=4.7 bits to be represented. Given this entrophy of 1.5 bits per character, can one simply answer this by:
(128/4.7) * 1.... |
Given a certain entrophy per character, how long should a passphrase be to guarantee key strength? |
Correct me if I'm wrong, but it sounds like the question is really, "If I encrypt a document multiple times with different keys in ECB mode, does the [common vulnerability of patterns][1] in plaintext showing in ciphertext go away?"
The answer to this is no. Consider a simple cipher which has the following mappings:... |
The protection scheme I faced recently seems so weak nowadays that a simple exhaustive key search would be enough to recover the user key in an acceptable amount of time (it's OK, since almost no practical benefit could be gained from knowing the plaintext), but I'm just curious whether the key recovery could be accomp... |
Have you considered using symmetric key crypto (MAC) instead ?
Elliptic Curve Crypto or even regular (but costly) modular arithmetic might be overkill in your case.
As I understand it you would be able to precharge MAC keys into your master and slaves before deployment and you would be set. You can even generate a... |
For your application: "I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realistic... |
For your application: "I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realistic... |
Theoretically, when using a symmetric block cipher in CBC mode, the current block is dependent on the previous block, so if one plaintext is encrypted using CBC, and then one bit of it is changed, lets say somewhere in the middle, then the new ciphertext will change from the middle onward. Would it be better if I used ... |
For your application: "I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realistic... |
For your application: "I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realistic... |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
This started as a comment to [CodeinChaos's answer](http://crypto.stackexchange.com/a/7929/555), but did not fit. I'm trying to regurgitate, in layman's terms, my understanding of the consequences on $\operatorname{SHA-256d}$ of the paper he quotes: [Dodis, Y., Ristenpart, T., Steinberger, J., & Tessaro, S. (2012). To ... |
I had an idea earlier:
Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a salt between sites, and include the site's name? For example:
SHA256("kFnU7Ra%P1_stackexchange")
SHA256("kFnU7Ra%P1_google")
And so on. As long as nobody gets your salt, it see... |
Using hash as password? |
Using salted hash as password for easy memorization without reuse? |
Theoretically, when using a symmetric block cipher in CBC mode, the current block is dependent on the previous block. Suppose one plaintext is encrypted using CBC, and then one bit of it is changed, let's say somewhere in the middle. Then the new ciphertext will change from the middle onward. Would it be better if I us... |
The question has morphed over time. I am answering the following.
>So to be sure, with DES, only when you encrypt something twice with a weak key. You get the back the original plaintext?
That is correct as that is the definition of a DES weak key, a key for which encryption and decryption have the same effect.
... |
The question has morphed over time. I am answering the following.
>So to be sure, with DES, only when you encrypt something twice with a weak key. You get the back the original plaintext?
That is correct as that is the definition of a DES weak key, a key for which encryption and decryption have the same effect.
... |
In my project we would like to **encrypt and authenticate** the the **communication channel** between our server and our Arduino nodes, which relies on an underlying TCP channel.
We have chosen **AES in CTR mode** as the cryptographic cipher of our choice, transmitting the initialization vector and the message numbe... |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
What's the state of the attack to get the first preimage on MD4?
Is it still this http://www.di.ens.fr/~leurent/files/MD4_FSE08.pdf in 2^102 ? |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
I had an idea earlier:
Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example:
SHA256("kFnU7Ra%P1_stackexchange")
SHA256("kFnU7Ra%P1_google")
And so on. As long as nobody discovers you... |
The [Wikipedia article on SHA-3](http://en.wikipedia.org/wiki/SHA-3) says that Keccak has been chosen but the standard hasn't been issued. Does this matter?
That is, can we just assume it's going to be as specified by the submitters (specifically for SHA-3-256 it's the Keccak-f-1600 permutation, in a sponge constru... |
Any point in waiting for the SHA-3 standard? |
The [Wikipedia article on SHA-3](http://en.wikipedia.org/wiki/SHA-3) says that Keccak has been chosen but the standard hasn't been issued. Does this matter?
That is, can we just assume it's going to be as specified by the submitters (specifically for SHA-3-256 it's the Keccak-f-1600 permutation, in a sponge constru... |
My securities instructor recently posed this question to the class and I am bending my brain in half trying to figure it out.
Suppose y1 = AES(K, x1) and y2 = AES(K,x2), and suppose you know the pairs (x1,y1) and (x2,y2). Without knowing K, how can you construct a new pair (x3,y3) such that y3 = AES(K,x3)?
It se... |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
I have some questions regarding aforementioned subject:
- Is there a EC equivalent of RSA-OAEP key transport/encryption algorithm ?
- Is ECIES-KEM sufficient ? |
I have found an encryption algorithm named ECKS-PS (published in the paper *Efficient conjunctive keyword search on encrypted data storage system*) that allows an user to search in encrypted data. All the steps are described here:
![definitions][1]
And I have written them a little bit more clear here:
![handw... |
In a paper it says "In the generic group model, the PRF is adaptively secure for inputs of $\mathbb{Z}_q^n$". Maybe a stupid question, but what does "adaptively secure" exactly means? |
What means "adaptively secure"? |
How would you generate a list of distinct random strings, where all strings are alphanumeric and have a fixed length? |
How to generate a list of unique random strings? |
In a paper it says "In the generic group model, the PRF is adaptively secure for inputs of $\mathbb{Z}_q^n$". Maybe a stupid question, but what does "adaptively secure" mean exactly? |
What does "adaptively secure" mean? |
My securities instructor recently posed this question to the class and I am bending my brain in half trying to figure it out.
> Suppose $y_1 = AES(K, x_1)$ and $y_2 = AES(K,x_2)$, and suppose you know the pairs $(x_1,y_1)$ and $(x_2,y_2)$. Without knowing $K$, how can you construct a new pair $(x_3,y_3)$ such that ... |
I've read a lot about protocols for mental poker without a trusted server, but I'm interested in the possibility of a faster, more practical protocol that relaxes that criterion a bit and "trusts" a third-party server whose trustworthiness can be easily verified (or whose cheating can be easily proven).
For example,... |
Relaxed trust criterion for mental poker server? |
I have found an encryption algorithm named ECKS-PS (published in the paper *Efficient conjunctive keyword search on encrypted data storage system*) that allows an user to search in encrypted data. All the steps are described here:
![definitions][1]
And I have written them a little bit more clear here:
![handw... |
I have found an encryption algorithm named ECKS-PS (published in the paper *Efficient conjunctive keyword search on encrypted data storage system*) that allows an user to search in encrypted data. All the steps are described here:
![definitions][1]
And I have written them a little bit more clear here:
![handw... |
At this [work][1] at section $2.2$ concerning a possible application for the [BGN cryposystem][2] the author points out that if you want to encrypt a unit vector $\overrightarrow{u_l}$ of size $l$ then the naive way is to encrypt each byte separately. And by following the idea of BGN the size of the ciphertext is reduc... |
Why unit vectors should be encrypted bit per bit in that case? |
At this [work][1] at section $2.2$ concerning a possible application for the [BGN cryposystem][2] the author points out that if you want to encrypt a unit vector $\overrightarrow{u_l}$ of size $l$ then the naive way is to encrypt each byte separately. And by following the idea of BGN the size of the ciphertext is reduc... |
At this [work][1] at section $2.2$ concerning a possible application for the [BGN cryposystem][2] the author points out that if you want to encrypt a unit vector $\overrightarrow{u_l}$ of size $l$ then the naive way is to encrypt each bit separately. And by following the idea of BGN the size of the ciphertext is reduce... |
Assuming the following:
- Key is randomly generated is being used (32 bytes+)
- IV is also randomly generated
- Crypto random key generator is used
- Data being encrypted contains common bytes like `{` `}` and `"` and keys (like JSON)
Which of these modes (CTR, OCB) are more appropriate for storing sensiti... |
As said by Thomas in the comment, modern encryption algorithms should work for all kinds of data, regardless of whether the plaintext is partially known or not.
In both modes of operation, for stored data you should remember to get a new initialization vector and reencrypt your whole "message" when changing any part... |
To walk you through RSA from start to end, here's how it works.
1. Choose two large distinct primes $p$, $q$. Calculate $n=pq$.
2. Calculate $\phi(pq)$. This happens to be $(p-1)(q-1)$.
3. Choose $e$ such that $gcd(e, \phi(pq)) = 1$ and $1 < e < \phi(pq)$.
4. Compute $d$ such that $de = 1 \mod \phi(pq)$.
5. Do s... |
Assuming the following:
- Key is randomly generated is being used (32 bytes+)
- IV is also randomly generated
- Crypto random key generator is used
- Data being encrypted contains common bytes like `{` `}` and `"` and keys (like JSON)
Which of these modes (CTR, CBC) are more appropriate for storing sensiti... |
I'm trying to make a PRG using the [Rabin function][1]. The code (in Java) I wrote to implement the function is:
poublic static int rabinFunction(int m, int publicKey) {
return (int) Math.pow(m, 2) % publicKey;
}
A trivial usage (using the numbers from the wikipedia link) would be:
int m = 20;
i... |
As said by Thomas in the comment, modern encryption algorithms should work for all kinds of data, regardless of whether the plaintext is partially known or not.
In both modes of operation (CTR and CBC), for stored data you should remember to get a new initialization vector and reencrypt your whole "message" (or data... |
As said by Thomas in the comment, modern encryption algorithms should work for all kinds of data, regardless of whether the plaintext is partially known or not.
In both modes of operation (CTR and CBC), for stored data you should remember to get a new initialization vector and reencrypt your whole "message" (or data... |
Is there an existing [AEAD](http://en.wikipedia.org/wiki/AEAD_block_cipher_modes_of_operation) scheme such that, for inputs with the same AD and IV,
<br><br><br>
$\:$ ciphertexts are allowed to leak whether or not their plaintexts are equal
$\;\;$ and
$\:$ if the scheme can process the plaintext in a streaming ... |
Is there an existing AEAD scheme with minimal IV requirements? |
Is there an existing [AEAD](http://en.wikipedia.org/wiki/AEAD_block_cipher_modes_of_operation) scheme such that, for inputs with the same AD and IV
1. ciphertexts are allowed to leak whether or not their plaintexts are equal,
2. if the scheme can process the plaintext in a streaming manner, then it is allowed t... |
I haven't been able to find a clear explanation on this (and i'm probably just confused in general). I have the following implementation of ElGamal:
- p = safe prime
- q = (q-1)/2
- g = an element of F$_p$ with order q.
- r = random 1 < r < q
- s = private
- Y = public
My question is, is there ... |
ElGamal: Generation of "g" value? |
I haven't been able to find a clear explanation on this (and I'm probably just confused in general). I have the following parameters of [ElGamal signatures](http://en.wikipedia.org/wiki/ElGamal_signature_scheme):
- p = safe prime
- q = (p-1)/2
- g = an element of F$_p$ with order q.
- r = random 1 < r <... |
I haven't been able to find a clear explanation on this (and I'm probably just confused in general). I have the following parameters of [ElGamal signatures](http://en.wikipedia.org/wiki/ElGamal_signature_scheme):
- $p$ = safe prime
- $q = (p-1)/2$
- $g$ = an element of $F_p$ with order $q$.
- $r$ = random $1... |
This seems OK assuming you can trust the authentication servers to leak neither the private key nor the deciphered passwords; and, if you use RSA, assuming you use a standard encryption padding with randomization, e.g. one of the two RSAES schemes in [PKCS#1][1].
Elgamal indeed can give you shorter cryptograms, whic... |
This seems OK assuming you can trust the authentication servers to leak neither the private key nor the deciphered passwords; and, if you use RSA, assuming you use a standard encryption padding with randomization, e.g. one of the two RSAES schemes in [PKCS#1][1].
Elgamal indeed can give you shorter cryptograms, whic... |
For your application: "_I need the (underpowered 8-bit) slave to be able to tell if a command issued is really trustable_", RSA signature with low public exponent ($e=3$), or Rabin (an analog with $e=2$), is likely the most appropriate, assuming you can't trust the slaves to keep a key secret, which is the only realist... |
If have application that is sending username and hashed password to server for authentication, how would I use salt for this scenario ? |
How to use salt if I am sending hashed password? |
We have the following two-party protocol between Alice and Bob. Alice sends messages $m_1, m_2, \ldots \in_R \mathbb{Z}_n^*$ to Bob and Bob signs these values by calculating $v_1, v_2, \ldots \in_R \mathbb{Z}_n^*$ and
$a_1 = \left( G \cdot H^{-v_1} \cdot K^{-m_1} \right)^{1/x}\ \bmod\ n$
$a_2 = \left( G \cdot H^{-v... |
I am read this example: A _random oracle_ is an ideal object; see [this previous question][1] for some details. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not try it. For instance, consider the following encryption scheme:
- $H$ is a ... |
I am read this example: A _random oracle_ is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not try it. For instance, consider the following encryption scheme:
- $H$ is a random oracle which outputs $n$-bit values.
- Th... |
I am reading this example:
> A _random oracle_ is an ideal object.
> What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not try it. For instance, consider the following encryption scheme:
> - $H$ is a random oracle which outputs $n$-bit... |
How can I prove that this encryption scheme from a random oracle is secure? |
Assuming that $x$ is odd, then the answer is no for number (1); to the best of our knowledge, the attacker would not be able to either compute (1/x) or factor N, even with a huge number of sets $(a_i, v_i, m_i)$, even if he got to select the $m_i$ (and even the $v_i$) values.
This follows directly from the fact that... |
i Have `eleven ciphertext` that encrypted with `same key`. i want to decrypt last ciphertext. I read similar question `like http://crypto.stackexchange.com/questions/6020/many-time-pad-attack` but i can't solve my problem with their answer.i'm new in crypto can any one tell what can i do?
i know when XOR two cipherte... |
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