instruction stringlengths 15 30k |
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Starting from uniformly random generated AES master key, is there a reference that prove that an specific roundkey can be considered as uniformly random generated as well ?
|
Is there a reference that prove that the AES Key Schedule generate random looking round keys? |
There have been some research in Optimal Extension Fields (OEF), introduced at Crypto'98 by Bailey and Paar [paper][1].
The idea is to work in a field $GF(p^n)$ with $p$ prime and of the form $2^{32}\pm c$ with small $c$ for 32-bit CPUs ($2^{64}\pm c$ for 64-bit CPUs), so that they can leverage on CPU's ALU for most... |
I'm working on understanding and implementing
> Damgård, I., & Dupont, K. (2005). Efficient Threshold RSA Signatures with General Moduli and No Extra Assumptions. Public Key Cryptography-PKC 2005, 346–361. doi:10.1007/978-3-540-30580-4_24. Retrieved from http://www.iacr.org/cryptodb/data/paper.php?pubkey=3431
On pa... |
I'm trying to solve a question about one time pads but I'm not sure if my assumptions are correct.
I am to assume that I have a one time pad with perfect secrecy. This one time pad is used to encrypt a message of 7 bits in length (message space size is 2^7). This encryption yields a ciphertext of "0110011". What is... |
It seems that merkle hash tree (MHT) traversals have been discussed somewhat in the literature, but there does not appear to be much written on inserting, deleting, and updating leaves. Is this lack of material regarding updating MHT's possibly due to the fact that the data (e.g. one time signatures) hashed to form MHT... |
Do any stream ciphers with aperiodic keystreams exist? |
Well, it's easy to show that any generated with a bound on the amount of internal state must eventually become periodic. It's also easy, once we allow a generator whose internal state grows arbitrary large over time, to design a generator that never repeats (and the state growth required is actually quite reasonable).... |
**Are there fallacies in above argumentation and is it a reasonable scheme?**
It's not unheard of to encrypt secrets for them to be decrypted by a HSM or smart card. Usually though the smart card or HSM itself is used to encrypt/decrypt stored secret values. I know that at least one HSM does this, and all TPM's out ... |
I cannot understand why a one-way function $f$ is defined in this way
$\text{Pr}(f(A(f(x))) = f(x)) < \frac{1}{p(n)}$
and not
$\text{Pr}(A(f(x)) = x) < \frac{1}{p(n)}$
where $A$ is a randomized algorithm.
Where is the difference? Is the second one weaker? Thank you!
|
When using the parallel version of Pollard's Rho algorithm for discrete logs, each processor performs its own random walk to find distinguished points, and reports the starting point and the distinguished point to the server. If two processors report the same distinguished point, then the server can re-do the random wa... |
In [Groth-Sahai NIZK][1] proof system, they have defined something called Quadratic Equation in $\mathbb{Z}_n$ as shown below. But, my idea of quadratic equation was a second order polynomial equation in a single variable, something of the form $ax^2 + bx + c = 0$. Then how is the below equation a quadratic one?
![e... |
Why is it a quadratic equation? |
Let us say we have three different plaintexts (all alphabets, A-z): *x*, *y* and *z*, each of length 21. Let the key, *a*, be also of length 21.
Now, what we have is *x^a*, *y^a* and *z^a*. How can we find out x, y and z from this?
I have looked around the web and found that the usual way to break this is to do s... |
XOR cipher with three different ciphertexts and repeated key, key length known. How do I find the plaintexts? |
Let us say we have three different plaintexts (all alphabets, A-Z): $x$, $y$ and $z$, each of length $21$. Let the key, $a$, be also of length $21$.
Now, what we have is $x \oplus a$, $y \oplus a$ and $z \oplus a$. How can we find out $x$, $y$ and $z$ from this?
I have looked around the web and found that the usu... |
I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, I'm trying to implement HSM.
The scheme goes as follows:
1. given a secret (e.g. 512 characters long string)
1. generate a public & private key pa... |
Can public key be recovered from ciphertext & encrypted private key? |
Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob.
Bob stores the decrypted message and the digital signature in a database.
However Alice is a bad girl and erases all data from her side, including her private/public keys. She then claims she never sent the message.
Is there a... |
When using the parallel version of Pollard's Rho algorithm for discrete logs, each processor performs its own random walk to find distinguished points, and reports the starting point and the distinguished point to the server. If two processors report the same distinguished point, then the server can re-do the random wa... |
I am trying to implement a cyclic group generator in Java, but I am running into some issues. In many cryptosystems, the following phrase is expressed during the key generation stage.
> Let G be cyclic group of prime order q and with a generator g
I have done some research on this and have been able to implement ... |
The best one i've seen actually uses SOS as a clue. RQ indicates a question, there fore you get "SOS?"
this seems to hint at a pattern, and then you get a few palindromes in the decoded morse, so:
everything that is symmetrical:
ISI (from invisible)
ESe (slightly weak due to the "e" from FORCESe)
From INTERPRETATI... |
One way to do this, if you're working with a multiplicative group $Z^*_p$, is to pick a prime $p$ so that $p-1$ has a large prime factor $q$; once you have this, then to generate a generator of order $q$, you pick a random value $h$, compute $g = h^{(p-1)/q}$, and if that is not 1, then $g$ is a generator of your group... |
Now, if we were to go round by round, you could give a distinct reason for not using a single round since after just one round, the right half of the text comes directly, as-is, to form the left half of the new text after the one round. In this way, if an observer were to notice this, he/she could deduce that DES may b... |
Why does the DES crypto algorithm NOT use 2 rounds? |
I know that encryption decryption happens as per following
Encrypt(PlainTextBytes, KeyBytes){
for(int i = 0;i < PlainTextBytes.length; i++) {
Cipherbytes[i] = PlainTextBytes[i] ^ KeyBytes[i];
}
return Cipherbytes;
}
... |
Getting Source Messages from encrypted Messages , XOR? |
If I got it right, chosen ciphertext security implies also CPA security. In other words, attacker can submit plaintexts to the challenger (along with ciphertexts).
I do not understand why encryption system (E,D) where D(k,0)=0 is considered as ciphertext secure.
Imagine CPA security game where an attacker just su... |
If I got it right, chosen ciphertext security implies also CPA security. In other words, attacker can submit plaintexts to the challenger (along with ciphertexts).
![enter image description here][1]
I do not understand why encryption system (E,D) where D(k,0)=0 is considered as ciphertext secure.
Imagine CPA s... |
I know that encryption decryption happens as per following
Encrypt(PlainTextBytes, KeyBytes){
for(int i = 0;i < PlainTextBytes.length; i++) {
Cipherbytes[i] = PlainTextBytes[i] ^ KeyBytes[i];
}
return Cipherbytes;
}
... |
Is there any security risk in encrypting parts of blocks twice? I'd like to get around block sizes and make encrypted messages just as long as the unencrypted ones:
<Blockquote>
**Block 1**: Byte 0 - 7<br>
**Block 2**: Byte 8 - 15<br>
**Block 3**: Byte 16 - 23<br>
**Block 4**: Byte **21** - 29<br>
</blockquote>... |
Decrypt a message which is encrypted using XOR and block-cipher? |
This is puzzle asked in a contest given that encryption , decryption happens as per following rule/code
Encrypt(PlainTextBytes, KeyBytes){
for(int i = 0;i < PlainTextBytes.length; i++) {
Cipherbytes[i] = PlainTextBytes[i] ^ KeyBytes[i];
}
... |
This is a puzzle asked in a contest.Given that encryption , decryption happens as per following rule/code .
Encrypt(PlainTextBytes, KeyBytes){
for(int i = 0;i < PlainTextBytes.length; i++) {
Cipherbytes[i] = PlainTextBytes[i] ^ KeyBytes[i];
}
re... |
This is a puzzle asked in a contest. Given that encryption , decryption happens as per following rule/code:
Encrypt(PlainTextBytes, KeyBytes){
for(int i = 0;i < PlainTextBytes.length; i++) {
Cipherbytes[i] = PlainTextBytes[i] ^ KeyBytes[i];
}
re... |
Decrypt a message which is encrypted using XOR? |
This is a puzzle asked in a contest. Given that encryption , decryption happens as per following rule/code:
Encrypt(PlainTextBytes, KeyBytes){
for(int i = 0;i < PlainTextBytes.length; i++) {
Cipherbytes[i] = PlainTextBytes[i] ^ KeyBytes[i];
}
re... |
Why no stateless and deterministic encryption system can be CPA-secure?
Is there a formal proof for it? |
Read the title. I've seen in RFCs that some MAC functions are called "pseudorandom functions". What are those? How are they different than hash functions? Why can't a hash function be used instead? |
What is the difference between a hash function and a pseudorandom function? |
Posted on bitcoin.stackexchange.com, but they referred me here.
You can see a little background about this on this [bitcointalk post](https://bitcointalk.org/index.php?topic=3238.0) by the late Hal Finney.
Beta and lambda are the values on the secp256k1 curve where:
λ^3 (mod N) = 1
β^3 (mod P) = 1
As see... |
How do you derive the lambda and beta values for endomorphism on the secp256k1 curve? |
RSA seems a bit creepy after the Snowden revelations and i'm looking for a simple python based blind signature library to fiddle around with. So far i've been unable to find anything. What am i missing? |
In fact, I want to implement a pseudorandom function based on GGM's construction at http://crypto.cs.uiuc.edu/wiki/index.php/GGM_PRF, but I need to get a doubling length PRG first while I cannot find any effective ways to do this. Can anybody help me or give me another way to implement a pseudorandom function? Any answ... |
What's the differences between the concept "pseudorandom generator" & "pseudorandom number generator"? |
You can see a little background about this on this [bitcointalk post](https://bitcointalk.org/index.php?topic=3238.0) by the late Hal Finney.
$\beta$ and $\lambda$ are the values on the secp256k1 curve such that:
$$\begin{align}
\lambda^3 &= 1 \mod N \\
\beta^3 &= 1 \mod P \\
\end{align}$$
As seen [here](http... |
What's the differences between the concepts “pseudorandom generator” and “pseudorandom number generator”?
In fact, I want to implement a pseudorandom function based on GGM's construction at http://crypto.cs.uiuc.edu/wiki/index.php/GGM_PRF, but I need to get a doubling length PRG first. I cannot find any effective wa... |
I'm studying the paper [*Fully Homomorphic Encryption over the Integers*](https://eprint.iacr.org/2009/616.pdf) by Marten van Dijk, Craig Gentry, Shai Halevi and Vinod Vaikuntanathan.
I have questions about the proof of Lemma A.1.
In page 6, the element of public key is in the form of $x=pq+r$
and the encryp... |
What's the differences between the concepts “pseudorandom generator” and “pseudorandom number generator”?
In fact, I want to implement a pseudorandom function based on GGM's construction at http://crypto.cs.uiuc.edu/wiki/index.php/GGM_PRF, but I need to get a doubling length PRG first. I cannot find any effective wa... |
Is the following MAC secure?
For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:f(k,i) \cdot g^{y_i \cdot r_i} \bmod p$.
Where $p$ is a prime number, $g \in \mathbb{G}$,$f(k,i)$ is a pseudorandom function whose output is distributed uniformly random over $\mathbb{G}$, $k$ is a $l$ bit key, and $i$ i... |
Is the following MAC secure?
For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$.
Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is a pseudorandom function whose output is distributed uniformly random over $\mathbb{G}$, $k$ is a $l$ bit key, and $... |
Is the following MAC secure?
For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$.
Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is a pseudorandom function whose output is distributed uniformly random over $\mathbb{G}$, $k$ is a $l$ bit key, and $... |
Is the following MAC secure?
For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$.
Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is a pseudorandom function whose output is distributed uniformly random over $\mathbb{G}$, $k$ is a $l$ bit key, and $... |
Is the following MAC secure?
For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$.
Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is a pseudorandom function whose output is distributed uniformly random over $\mathbb{G}$, $k$ is a $l$ bit key, and $... |
Why can no stateless and deterministic encryption system be IND-CPA secure?
Is there a formal proof for it? |
In the paper [Ring Signatures of Sub-linear Size Without Random Oracles][1], authors have remarked that the scheme is instantiable in composite order setting, too. I am attaching the following reference below. Can anyone please help me in understanding the argument I have highlighted?
![enter image description here]... |
I'm working on a web site for a private company that should allow them to upload files, which will be later retrieved by their affiliates. The site will be available from a public Internet using private URLs for each uploaded file. All files uploaded will be encrypted-and-MAC'ed using AES-256 encryption. Files could be... |
I had a quiz last week in computer security course. There was a confusing question that I am still looking for a good and clear answer.
First, I know that counter mode with a good block cipher is widely accepted and most likely unbreakable as long as the counter (IV) is not being reused.
The question was about u... |
Counter Mode with a sequence of zeros bits plaintext, is it secure? |
Multi-prime RSA is now a well known technique: it uses $k>2$ distinct secret prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed boost in private-key operation, with little (conjectured) reduction in security for small-enough $k$; the speedup factor relative to 2-pr... |
I had a quiz last week in computer security course. There was a confusing question that I am still looking for a good and clear answer.
First, I know that counter mode with a good block cipher is widely accepted and most likely unbreakable as long as the counter (IV) is not being reused.
The question was about u... |
I know factoring is the chief means of breaking RSA keys. I know an algorithm that runs in polynomial time would be able to break an RSA key pair "quickly". But how quickly is "quickly"? Note, I'm not talking about any quantum computing at all here. |
How fast would a polynomial time factoring algorithm compute? |
> I know an algorithm that runs in polynomial time would be able to break an RSA key pair "quickly". But how quickly is "quickly"?
No way to say, it might be microseconds, and it might be large multiplies of the age of the universe.
When we say that an algorithm runs in polynomial time, we're not saying anything ... |
I'm writing a small script that generates random non-signed decimal integers within a certain range of values. I'm using GNU "od", with the following command:
od /dev/hwrng --address-radix=n --read-bytes=4 --format=u4
/dev/hwrng is linked to a SoC thermal noise sensor (bcm2708 on Raspberry Pi), so it would re... |
Does using modulo (%) affect quality of randomness? |
Let me begin by saying that if you have a hardware source of randomness, you don't need to be stingy with it.
**1) Does modulo affect the quality of randomness, faking in some way the distribution of values?**
Yes, it does. Or at any rate, it can --- see my answer to (3) below for more details. (I'm assuming by "... |
It was from frequency analysis lecture and the professor mentioned but I cannot recall.
The K value for English was .067, German was .076. The lowest K was Russian which was .056. When the frequency is uniform among 26 letters, then K is .038.
What is the complete word that K stands for? |
I've been looking into the difference between PRNGs and proper RNG techniques. One that I particularly like is the idea of tuning a radio to a certain frequency and bandwidth and just listening to the noise. Every so often (or continuously) pick a sample out of the noise and build a random number out of the samples.
... |
Is Sage a better alternative to C++(with NTL), for programming that involves math objects like polynomial rings in cryptosystems? I hear that Sage is an open source alternative to Magma. I have used Magma before for such programming and it was easier than using C++ because it had built in keywords for defining such str... |
I am doing Project under the topic CP-ABE.I need to generate a symmetric bilinear group Go of prime order p and with generator g...Then how to choose random elements from Zp....kindly anyone help me...Is it possible to do this with Java? |
Is there a encryption scheme in literature, where I can do something like
$$F_{k_1}^{-1} \big( F_{k_2}(A) + R \big) = A + O(R)$$
where, $A$ is a $m \times n$ real matrix, $R$ is a $m \times n$ real matrix that contains some random noise, and (preferably, $k_1 \neq k_2$)
essentially what I want is a scheme whe... |
Let me begin by saying that if you have a hardware source of randomness, you don't need to be stingy with it.
**1) Does modulo affect the quality of randomness, faking in some way the distribution of values?**
Yes, it does. Or at any rate, it can --- see my answer to (3) below for more details. (I'm assuming by "... |
Let me begin by saying that if you have a hardware source of randomness, you don't need to be stingy with it.
**1) Does modulo affect the quality of randomness, faking in some way the distribution of values?**
Yes, it does. Or at any rate, it can --- see my answer to (3) below for more details. (I'm assuming by "... |
Imagine that P=NP, and one way functions don't exist. Can two people end up with a random shared key of arbitrary length, if every exchange is public? They have true RNGs, and know who they are talking to (we're not worried about mitm attacks).
There is also someone else sharing the channel, who has one time pads wi... |
Can you exchange a shared key without any hardness assumptions? |
I was being argued that stream cipher's key that is the length of the message must be sent to the destination for them to be able to decrypt the message.
My point is don't you only have to send the seed of the PRG let's say the 128 bits key for RC4 128 and then the destination can recreate the full length key from t... |
I'm writing a small script that generates random non-signed decimal integers within a certain range of values. I'm using GNU `od`, with the following command:
od /dev/hwrng --address-radix=n --read-bytes=4 --format=u4
`/dev/hwrng` is linked to a SoC thermal noise sensor (bcm2708 on Raspberry Pi), so it would ... |
I'm reading a protocol specification where the procedure is to generate a CMAC, take the first 4 bytes of it, appending it to the message and then encrypt the message + CMAC together with another key.
So there is a key for integrity, and a key for encryption.
Does that add any extra security really? I thought CM... |
Is there any advantage on encrypting the CMAC together with the message? |
I'm reading a protocol specification where the procedure is to generate an AES-128 CMAC, take the first 4 bytes of it, appending it to the message and then encrypt the message + CMAC together with another key using AES-128-CTR.
So there is a key for integrity, and a key for encryption.
Does that add any extra se... |
where $g$ is a group element in bilinear group $\mathbb{G}$. I understand it is very similar to the conventional DBDH problem, but $g^{1/b}$ is also known, possibly making it easier? Does anyone know the answer or suggest some material for reference? Thanks. |
Given $g^a, g^b, g^c, g^{1/b}$, is it hard to compute $e(g, g)^{abc}$ or $e(g, g)^{ac/b}$? |
Given $g^a, g^b, g^c, g^{1/b}$, is it hard to distinguish $e(g, g)^{abc}$ or $e(g, g)^{ac/b}$ from a random value? |
Given $g^a, g^b, g^c, g^{1/b}$, is it hard to distinguish $e(g, g)^{abc}$ from a random value? |
In Blum Blum Shub, the generator is $x_{n+1}={x_n}^2 \mod M$ where $M=p \cdot q$, $p \in \mathbb P$, and $q \in \mathbb P$. Supposedly, knowing $p$ and $q$ is enough to break the system. But if I know M, I can calculate the next number in the sequence, so there is no need to know the two factors. Why isn't that suffici... |
Why is knowing M not enough to break Blum Blum Shub? |
Your questions:
> if all the clients leave the group (at which moment they delete K from their local store), all the information on the server will be useless as nobody has K anymore
> if Client2 comes online for the first time and another group member is not online it will not be able to obtain K and will not be a... |
I have a secret message which I want to encrypt such that any of several different keys can open it independently. The keys can't know about each other and it has to be able to work completely locally without a network. In short I want two functions
encrypt(message, key1, key2, key3, ...) -> code
decrypt(... |
I'm reading a protocol specification where the procedure is to generate a CMAC, take the first 4 bytes of it, append this authentication tag to the message and then encrypt the message + CMAC together with another key using CTR mode encryption.
Both CMAC and CTR mode are defined to use the AES-128 block cipher.
A s... |
Given that $f$ is a OWF and $|f(x)|=|x|$ for all $x$, is $g(x)=f(x)\oplus x$ necessarily also a OWF? |
Is $f(x)\oplus x$ a one-way function? |
I have recently been playing with Chacha20-Poly1305 with libsodium, and all of the examples state the additional data portion of the tag is stored in plaintext when encrypted. But from what I can tell the AD tag never actually gets put anywhere in the ciphertext. So if I were to simply transfer the ciphertext I would n... |
I have recently been playing with Chacha20-Poly1305 with libsodium, and all of the examples state the additional data portion of the tag is stored in plaintext when encrypted. But from what I can tell the AD tag never actually gets put anywhere in the ciphertext. So if I were to simply transfer the ciphertext I would n... |
[Full Boneh-Boyen signature scheme][1] defines a pair of secret keys (SK) $a \in \mathbb{Z}_n$ and $b \in \mathbb{Z}_n$ and a pair of public keys (PK) $A = G^a \in \mathbb{G}$ and $B = G^b \in \mathbb{G}$. Can anybody point me out to some similar signature scheme where $SK \in \mathbb{Z}_n$ and $PK \in \mathbb{G}$?
... |
In Blum Blum Shub, the generator is $x_{n+1}={x_n}^2 \mod M$ where $M=p \cdot q$, $p \in \mathbb P$, and $q \in \mathbb P$. Supposedly, knowing $p$ and $q$ is enough to break the system. But if I know M, I can calculate the next number in the sequence, so there is no need to know the two factors. Why isn't that suffici... |
We know that the one-time pad is provably secure as a cipher to encrypt some data. Is there an algorithm which does the same just as a hash function? Can we get a provably secure hash function? Maybe with some ridiculous properties like the one-time pad got them (really big key length, fully random key)? |
Hash function as secure as one-time pad? |
Openssl block ciphers return length of the text as output of the encryption (`envelope_seal()`), and If I have to send the `length` over network, I append the length with the `ciphertext` as I can transmit only one field and `envelope_open()` needs the `length` of the `ciphertext`. Is there any other way that I can cal... |
There was a time when I wondered about multiplication as an encryption operation. That was when I was thinking in terms of modular multiplication. But how about based around simple multiplication.
Pretend $M$ is a message represented as a number. $K$ is the secret key. Encryption is $C=M \times K$ and decryption is ... |
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