instruction stringlengths 15 30k |
|---|
What is the impact of the Goppa code distinguisher on the CFS and McEliece? |
Implementing a XOR cipher with a pseudo-random key equal to the length of plain text, Is there a significant difference in key strength between a character pool of 1000 and 5000? Or is this not likely to be a deciding factor in overall security for a simple XOR? |
Why is this MAC based on secure PRF with ordering and randomization insecure? |
Given:
* The attacker can call PRP() and the inverse function prp() on any message of his choosing.
* PRP is a [pseudorandom permutation][1] indistinguishable to the attacker from a random permutation.
* Assuming R and K are "sufficiently large", perfectly random, and never leaked to the attacker -- in particular,... |
How to pronounce RIPEMD 160? |
Given:
* The attacker can call PRP() and the inverse function prp() on any message of his choosing.
* PRP is a [pseudorandom permutation][1] indistinguishable to the attacker from a random permutation.
* Assuming R and K are "sufficiently large", perfectly random, and never leaked to the attacker -- in particular,... |
I'm reading [Collision-Resistant Hashing: Towards Making. UOWHFs Practical][1]. and here say that its formalization is non-asymptotic. Why the formalization is non-asymptotic?, Which will be a example of hash function with formlization asymtotic?
[1]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.77.2... |
I'm reading [Collision-Resistant Hashing: Towards Making UOWHFs Practical][1], and they
<br>
say that its formalization is non-asymptotic. Why is the formalization non-asymptotic?
<br>
What is an example of hash function with an asymptotic formlization?
[1]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=... |
When implementing a XOR cipher with a pseudo-random key equal in length to the plaintext, Is there a significant difference in potential key strength between keys drawn from a pool of either 1000 or 5000 possible characters? (that is, each character in the key may be any one of up to five thousand possible characters) ... |
From what I can remember, RSA is something like this:
* Generate 2 distinct prime numbers $p$ and $q$ that have similar bit length.
* Compute $n=pq$ and $\phi(n)=(p-1)(q-1)$
* Compute $e$ such that $1<e<\phi(n)$ and $\gcd(\phi(n),e)=1$. It is optimal for $e$ to be prime
* Compute $d$ such that $ed\equ... |
Why does plain RSA not work? |
From what I can remember, RSA is something like this:
* Generate 2 distinct prime numbers $p$ and $q$ that have similar bit length.
* Compute $n=pq$ and $\phi(n)=(p-1)(q-1)$
* Compute $e$ such that $1<e<\phi(n)$ and $\gcd(\phi(n),e)=1$. It is optimal for $e$ to be prime
* Compute $d$ such that $ed\equ... |
Why does plain RSA not work with big messages ($m>n$)? |
The issue is that we use modular arithmetic. In modular arithmetic, you may view $m \bmod n$ as the remainder of $m$ when divided by $n$. So, for example, $7 \bmod 2 = 1$, also written as $7 \equiv 1 \pmod 2$, because $2(3) + 1 = 7$.
Now consider what you're guaranteed by $m \equiv c^d \pmod n$, the decryption form... |
I have two keys **(K1 and K2)** at both the client and the server. I hope to use **HKDF** in both client and server side to concatenate the keys.
I will use the same salt value at both the client ad the server. Then will I be able to arrive at the same key by applying HKDF at both the client and the server to K1 and K... |
Is this new server API authentication protocol secure? |
**Assume:**
- $O$ be a reversible random permutation oracle on a finite set and $O^{-1}$ the inverse permutation *(pretty much equivalent to a random permutation: http://crypto.stackexchange.com/questions/11881)*. Here, the attacker can call both $O$ and $O^{-1}$ on any input
- $M$ be a fixed-length message to encr... |
In the paper [On the Security of the TLS Protocol: A Systematic Analysis](http://eprint.iacr.org/2013/339.pdf), the authors define the notion of a *stateful length-hiding authenticated encryption scheme* (sLHAE). For the purpose of this question you can just ignore the length-hiding part of sLHAE, since my question dea... |
Flaw in the security definition of Stateful Length-Hiding Authenticated Encryption (sLHAE)? |
Let's say A wants to send a message, so everyone who gets the message, can be assured that it's from A. A then sends a message :
`message|timestamp|E(A_private_key, Hash(message|timestamp))`
What are the benefits of timestamp? How can a person who gets the message know that it's the correct timestamp? Why just no... |
Why use a timestamp and how can someone know it's the correct one? |
In the paper [On the Security of the TLS Protocol: A Systematic Analysis](http://eprint.iacr.org/2013/339.pdf), the authors define the notion of a *stateful length-hiding authenticated encryption scheme* (sLHAE). For the purpose of this question you can just ignore the length-hiding part of sLHAE, since my question dea... |
What is adaptive zero-knowledge? |
Suppose E_k(a, b, c) is encryption of values a, b and c with key k through encryption algorithm AES (AES-128) and each a, b and c are 300 bits integer values.
now if V1= E_k(a, b, c) and V2= E_k(c, a, b)
my questions is:
The two values V1 and V2 are equals or not?
|
Does any of you know what is the difference between the Pedersen commitment and the commitment that uses the ElGamal encryption scheme?
For the sake of completeness, I recall what both of them look like.
Given two public and large primes $p$ and $q$ such that $q∣(p−1)$, and a (also public) generator $g$ of the o... |
Suppose $E_k$$(a, b, c)$ is encryption of values $a, b$ and $c$ with key $k$ through encryption algorithm AES (AES-128) and each $a, b$ and $c$ are 300 bits integer values. Also Suppose this algorithm in my question situation work in CBC mode.
now if $V_1= E_k(a, b, c)$ and $V_2= E_k(c, a, b)$
my questions is:
... |
Can you help me to finding some papers that shows AES is secure against known-plaintext attack? |
First let me apologize if this is an ill posed question. Let me also note that I do not in any way seek a comprehensive answer, simply your thoughts on what makes for a valuable asset to a company like the NSA. I am a Maths student in the US, and I realize that a problem-solving mind is at minimum required for said que... |
Suppose $E_k$$(a, b, c)$ is encryption of values $a, b$ and $c$ with key $k$ through encryption algorithm AES (AES-128) and each $a, b$ and $c$ are 300 bits integer values.
Also Suppose this algorithm in my question situation work in CBC mode.
If $V_1= E_k(a, b, c)$ and $V_2= E_k(c, a, b)$, my questions is: a... |
Given:
* The attacker can call PRP() and the inverse function prp() on any message of his choosing.
* PRP is a [pseudorandom permutation][1] indistinguishable to the attacker from a random permutation.
* Assuming R and K are "sufficiently large", perfectly random, and never leaked to the attacker -- in particular,... |
In SSSS, if you recreate the original secret with one of the decoder inputs being slightly damaged (e.g. one or two chars incorrect), you receive a slightly damaged version of the original secret. So if the original secret was "Abraham Lincoln", decoding using a slightly damaged input might still get you "Ab%aham Linco... |
I am wondering if it's possible to have a scheme as follows.
Here is the scenario:
- we have a set of objects (e.g. strings) {O1, O2, ..., On}
- we have a set of users {U1, U2, ..., Um}
- each user asks to compute a function over a subset of the objects
- we have an intermediate (trusted) component A that ... |
I am wondering if it's possible to have a scheme as follows.
Here is the scenario:
- we have a set of objects (e.g. strings) {O1, O2, ..., On}
- we have a set of users {U1, U2, ..., Um}
- each user asks to compute a special function f over a subset of the objects
- we have an intermediate (trusted) compone... |
I'm going to assume that the comma $,$ operator used in your question means 'concatenate' (normally written $a||b||c$). Moreover, I'm assuming that $a,b,c$ are distinct.
In that case, With incredibly high probability, No: $V_1$ and $V_2$ will not be equal.
Think of it this way: if they were equal, then what would... |
Simple question: we have AES 128 encryption and a key. How can we calculate the key check value (KCV)?
One example: key is 48C3B4286FF421A4A328E68AD9E542A4 and KCV should be 77DC84.
I am trying it out in C#, but there are just to many 'unknowns' for a newbie in cryptography...
Edit: there was a question why... |
How is the MD2 hash function S-table constructed from Pi? |
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 f... |
I have blinded m = 16 with r= 13, e = 7 and n = 209.
This resulted in m' = 464, which led to a s' = 8.
Now, I want to unblind this s' by using s = s' * r$^{-1}$ but im stuck at filling in the r$^{-1}$? |
Question. I present an algorithm that can find a prime factor of an n-bit binary number in polynomial time (actually factoring the number is just a refinement of this idea). Does this mean that the RSA protocol (and similar protocols) are not secure?
We consider a large n-bit number N written in binary. We want to... |
Is the RSA protocol secure? |
Question. I present an algorithm that can find a prime factor of an n-bit binary number in polynomial time (actually factoring the number is just a refinement of this idea). Does this mean that the RSA protocol (and similar protocols) are not secure?
We consider a large n-bit number N written in binary. We want to f... |
It is clear that when we have any output stream $x_0,x_1,...$ produced by linear feedback shift register than this output has to be periodic.
Now I was wondering if we can find an upper bound for the period of the output sequence from a linear feedback shift register with $R$ registers over $\mathbb F_q$?
|
In short: Is it cryptographically stronger to have a known length password of the maximum length allowed, or a random length password somewhere in the range of the longest length possible. Does the answer change depending on the max length? For instance my credit union (still!) forces a maximum length of 10 character... |
Yes, RSA is secure as we know it — although recommended key sizes are ever-increasing, as expected. Any seemingly-simple result that suggests a long-studied, well battle-hardened cryptosystem is insecure should throw up red flags.
As an exercise, I wrote up your algorithm in simple C code:
<!-- lang: c -->
... |
Having a random length makes very little total difference in the entropy of your password compared to the entropy you would get using just the maximum length allowed. This is because there are a lot more passwords of, say, length 10 than any smaller length (in fact, there are more 10-character passwords than any other ... |
Having a random length makes very little total difference in the entropy of your password compared to the entropy you would get using just the maximum length allowed. This is because there are a lot more passwords of, say, length 10 than any smaller length (in fact, there are more 10-character passwords than any other ... |
It is known that computing $a^x \bmod N$ takes $O(|x| + \mathrm{pop}(x))$ multiplications modulo $N$, where $|x|$ is the number of bits of $x$ and $\mathrm{pop}(x)$ is the number of $1$ bits (Hamming weight). This suggests a side channel attack by measuring the run time of the exponentiation.
Can the number of $1$ ... |
It is known that computing $a^x \bmod N$ takes $O(|x| + \mathrm{pop}(x))$ multiplications modulo $N$, where $|x|$ is the number of bits of $x$ and $\mathrm{pop}(x)$ is the number of $1$ bits (Hamming weight). This suggests a side channel attack by measuring the run time of the exponentiation.
Can the number of $1$ ... |
Between them, [K.G.](http://crypto.stackexchange.com/users/7863/k-g) and [Dilip Sarwate](http://crypto.stackexchange.com/users/819/dilip-sarwate) have pretty much answered your question. That is, you can derive *an* upper bound using the [method described](http://crypto.stackexchange.com/questions/11950/upper-bound-lin... |
Having a random length makes very little total difference in the entropy of your password compared to the entropy you would get using just the maximum length allowed. This is because there are a lot more passwords of, say, length 10 than any shorter length (in fact, there are more 10-character passwords than any other ... |
In short:
**Is it cryptographically stronger to have a known length password of the maximum length allowed, or a random length password somewhere in the range of the longest length possible?**
Does the answer change depending on the max length? For instance my credit union (still!) forces a maximum length of 10 ... |
Between them, [K.G.](http://crypto.stackexchange.com/users/7863/k-g) and [Dilip Sarwate](http://crypto.stackexchange.com/users/819/dilip-sarwate) have pretty much answered your question. That is, you can derive *an* upper bound using the [method described](http://crypto.stackexchange.com/questions/11950/upper-bound-lin... |
Between them, [K.G.](http://crypto.stackexchange.com/users/7863/k-g) and [Dilip Sarwate](http://crypto.stackexchange.com/users/819/dilip-sarwate) have pretty much answered your question. That is, you can derive *an* upper bound using the [method described](http://crypto.stackexchange.com/questions/11950/upper-bound-lin... |
How can I derive formulas for adding 2 points and multiplication by a scalar in Jacobian coordinates $(x,y) = (\frac{X}{Z^2},\frac{Y}{Z^3})$ over an elliptic curve? |
I don't seem to grasp why is the handshake for PTK in WPA2-PSK 4-way and not 2-way. Isn't it enough to just have these two steps:
1. First party sends Nonce1 to the other party
2. Second party sends to first party Nonce2 and the HMAC(Nonce1, Nonce2, other parameters) using KCK.
I don't understand why does first ... |
I want to be able to detect tampering in a log file that is under the control of an untrusted party. I am not interested in secrecy, only the integrity of the contents in the file - so I want to detect if entries have been removed/changed. The solution that I seem to have found from a short google search is to use hash... |
I've been reading about bcrypt and scrypt, and it seems that the general consensus is that bcrypt is more "tried and true", but scrypt is better in theory.
Couldn't you just hash something with bcrypt, then with scrypt? If it has a layer of scrypt to use resources, and a layer of bcrypt, shouldn't that give you the ... |
scrypt and bcrypt for benefits of both? |
Can someone explain, how a^x mod N can be speeded up, when a and N are known constants? And how big is the gain and what ressources are needed?
https://www.imperialviolet.org/2013/05/10/fastercurve25519.html |
I'm not quite sure at what level this question is set, so sorry if I start "too low" (or indeed don't reach an efficient enough goal!).
Let $x=x_n\dots x_1x_0=\sum_{i=0}^n x_i 2^i$ be the binary expansion of $x$, and let $a_j=a^{2^j}$.
**Very naively:**
$$
a^x \pmod N = \overbrace{a*(a*(a*\dots*(a))\dots))}^{\tex... |
I'm reading a notion Any Collision Resistance for Hash Functions. In the lecture define a collision finder CF.
> CF is said to $(t,\epsilon)$-break the family of hash functions $F_K$
> if the running time is at most $t$, and the probability that CF, on
> input K, outputs a collision $M,M'$ for $F_K$ is at least $... |
I'm not quite sure at what level this question is set, so sorry if I start "too low" (or indeed don't reach an efficient enough goal!).
Let $x=x_n\dots x_1x_0=\sum_{i=0}^n x_i 2^i$ be the binary expansion of $x$, and let $a_j=a^{2^j}\pmod N$.
**Very naively:**
$$
a^x \pmod N = \overbrace{a*(a*(a*\dots*(a))\dots))... |
*In brief: If you know $(a,N)$, you can speed the computation up by precomputing some of the powers of $a$.*
----------
Let $x=x_n\dots x_1x_0=\sum_{i=0}^n x_i 2^i$ be the binary expansion of $x$, and let $a_j=a^{2^j}\pmod N$.
**Very naively:**
$$
a^x \pmod N = \overbrace{a*(a*(a*\dots*(a))\dots))}^{\text{... |
Can someone explain, how $a^x \mod N$ can be speeded up, when $a$ and $N$ are known constants? How big is the gain and what resources are needed?
https://www.imperialviolet.org/2013/05/10/fastercurve25519.html |
Can someone explain, how $a^x \mod N$ can be speeded up, when $a$ and $N$ are known constants? How big is the gain and what resources are needed?
https://www.imperialviolet.org/2013/05/10/fastercurve25519.html
---
Just to mention: it can speed up SRP hashes bruteforce, which is calculated as $v = a^x \mod N$ wh... |
How can Shamir's method for secret sharing work in the GF(256)? |
Suppose one is implementing a cryptographic scheme over a group where one needs the discrete logarithm to be hard - what is the recommended group to use? I'm looking for a group where calculations are simple but it doesn't need to be extremely efficient. I would therefore prefer some type of multiplicative group mod n.... |
Best group if one wants the discrete log problem to be hard? |
I'm reading a notion Any Collision Resistance for Hash Functions. In the lecture define a collision finder CF.
> CF is said to $(t,\epsilon)$-break the family of hash functions $F_K$
> if the running time is at most $t$, and the probability that CF, on
> input K, outputs a collision $M,M'$ for $F_K$ is at least $... |
I am actually preparing for a cryptography exam, and I found a question asked by the professor in the class, below are the lines that I copied from the slide :
"
Example: Let Ek be the encryption transformation of one-key cipher and
h be a hash function. Then hk := Ek ◦ h is a keyed hash function, where ◦
denotes... |
Design requirements for a keyed hash function? |
I am actually preparing for a cryptography exam, and I found a question asked by the professor in the class, below are the lines that I copied from the slide :
> **Example:** Let $Ek$ be the encryption transformation of one-key cipher and
$h$ be a hash function. Then $hk := Ek ◦ h$ is a keyed hash function, where $... |
In this [paper][1] on pg. 1248 in the "preprocessing phase" section the authors say:
> In the preprocessing phase, the parties run a (standard) MPC to
> collectively generate a key pair (pk,sk) for the FHE scheme, and to
> secret share sk in such a way that (a) learning the shares of
> corrupted parties, and lea... |
How do you prevent the risk of damage to the security of Fully Homomorphic Encryption? |
In this [paper][1] on pg. 1239 the footnote at the bottom points out the difference between $joint$ leakage and $disjoint$ leakage. The authors say the weakly leakage resilient protocol of BGG+11 cannot be directly used because it only applies to $joint$ leakage.
My understanding is the adversary has been made mo... |
Why does a joint leakage MPC protocol not directly apply to a disjoint leakage requirement? |
We consider a large $n$-bit number $N$. We want to find a factor, if it admits any.
For $m$ taking values from $1$ to $n$, perform the following three steps (actually, for each $m$, perform many cycles, as described below).
1. Generate a random $m$-bit $x$.
2. If $x$ is a divisor of $N$, return $x$. Otherwise ... |
Is it possible to attack RSA with a WalkSat derivative? |
Does it make sense to reuse some of the keys from my PGP (gnupg, gpg) keyblock when generating my own SSL Certificate Authority?
In an ideal world people would have one keypair in a trustworthy hardware device, and they could use it to certify everything, e.g. their own SSL Certificate Authority (as opposed to gener... |
Reusing PGP key when generating SSL Certificate Authority? |
>Part (a) above makes me believe there is a risk with FHE security being damaged. Is it possible to use another encryption scheme where this risk is mitigated ?
I'm not sure what you mean by that. In what way is security damaged? All ciphers risk security being damaged by leakage. For example if the key leaks, secur... |
In continuation to [this][1] question: which else operations are used in symmetric cryptography and why?
What is the difference between addition modulo 2 (xor) and addition modulo 2 ^ register size (addition with overflow)?
Some similar questions:
- http://crypto.stackexchange.com/questions/2608/why-addition-m... |
No, two messages is not sufficient to achieve what the WPA2-PSK 4WHS is supposed to do: [mutual authenticated key-exchange](http://crypto.stackexchange.com/q/10644/1772).
The key term here is *mutual authentication*. Remember, at the start of the WPA2-PSK handshake we have two entities, the access point and the cli... |
I have doubts for the definition of the decryption algorithm $D(.)$. I think I've already seen that the decryption returns a plaintext $M$ on input the key $K$ and $C=E_K(M)$.
I have also seen thet the decryption algorithm returns either $M$ or the special symbol $\bot$.
Is the first definition valid in the case ... |
Evaluating, we have that
Sha_1(38607310235)=6502c8f9f5c222b9598d4e074fd3431f506948bc
So, I'm guessing the question you're actually asking is:
> Given an 11 digit number $x$, find $y$ such that $L[H(y)]=x$, where $L(\cdot)$ takes the last 11 hexadecimal characters, and $H(\cdot)$ is the SHA-1 hash function
... |
EDIT: Proposed this as an edit for the original poster, and so deleting this post
--------------------------------------------
Evaluating, we have that
Sha_1(38607310235)=6502c8f9f5c222b9598d4e074fd3431f506948bc
So, I'm guessing the question you're actually asking is:
> Given an 11 digit number $x$, find $... |
Evaluating, we have that
Sha_1(38607310235)=6502c8f9f5c222b9598d4e074fd3431f506948bc
So, I'm guessing the question you're actually asking is:
> Given an 11 digit number $x$, find $y$ such that $L[H(y)]=x$, where $L(\cdot)$ takes the last 11 hexadecimal characters, and $H(\cdot)$ is the SHA-1 hash function
... |
I have a task to find a the message for which the SHA-1 hash's last 11 symbols in hexadecimal presentation corresponds to an 11-digit number.
I have been given the following example solution:
> For the code `38607310235`, a solution is `a513b8c4507ea2891fb34cd4612e038607301235`, which is the hash of $y$
How can... |
Evaluating, we have that
Sha_1(38607310235)=6502c8f9f5c222b9598d4e074fd3431f506948bc
So, I'm guessing the question you're actually asking is:
> Given an 11 digit number $x$, find $y$ such that $L[H(y)]=x$, where $L(\cdot)$ takes the last 11 hexadecimal characters, and $H(\cdot)$ is the SHA-1 hash function
... |
Evaluating, we have that
Sha_1(38607310235)=6502c8f9f5c222b9598d4e074fd3431f506948bc
So, I'm guessing the question you're actually asking is:
> Given an 11 digit number $x$, find $y$ such that $L[H(y)]=x$, where $L(\cdot)$ takes the last 11 hexadecimal characters, and $H(\cdot)$ is the SHA-1 hash function
... |
In continuation to http://crypto.stackexchange.com/questions/8533/why-are-bitwise-rotations-used-in-cryptography: what other operations are commonly used in symmetric cryptography? Are there particular operations on numbers that are good for building ciphers? Do common ciphers tend to use the same basic building blocks... |
What operations are used in symmetric cryptography and why? |
I [sometimes][1] [see][2], in [discussions][3] of symmetric ciphers, reference to the 'key agility' of a particular algorithm. It seems to be related to the difficulty of switching encryption keys, but I don't understand more than that. Can anyone give a good explanation of 'key agility' and some contexts in which it i... |
What is 'key agility' in relation to symmetric-key encryption? |
after studying philosophy and being a philosophy teacher, I took back studies 4 years ago and I did a bachelor in maths. I'm in maths grad school now (I'm 32), and I would like to work in cryptography. (I took as many algebra and arithmetic and logic courses as I could, and I'm studying Galois theory this semester.)
I... |
I've been reading Brakerski and Vaikuntanathan's [Efficient Fully Homomorphic Encryption from (Standard) LWE][1] and I'm still digesting pieces at a time.
Under section 1.1, *Re-Linearization: Somewhat Homomorphic Encryption without Ideals*, they state they mask the plain text with noise. The noise is created with m... |
I've been reading Brakerski and Vaikuntanathan's [Efficient Fully Homomorphic Encryption from (Standard) LWE][1] and I'm still digesting pieces at a time.
Under section 1.1, *Re-Linearization: Somewhat Homomorphic Encryption without Ideals*, they state they mask the plain text with noise. The noise is created with m... |
I've been reading Brakerski and Vaikuntanathan's "[Efficient Fully Homomorphic Encryption from (Standard) LWE][1]" and I'm still digesting pieces at a time.
Under section 1.1, *"Re-Linearization: Somewhat Homomorphic Encryption without Ideals"*, they state they mask the plain text with noise. The noise is created wi... |
Homomorphic Encryption and Semantic Security using Lattices? |
I just find this pencil and paper cipher 'Felix' <del>on this [site][1]</del>
and I want to know how secure it is?
[1]: http://topcat.hypermart.net/felix.html |
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