instruction stringlengths 15 30k |
|---|
How exactly was the finalist chosen in the NIST AES competition? |
I am implementing AES 256-bit Algorithm from the Theory given in the book, "Cryptography and Network Security" by Behrouz A. Forouzan.
The Algorithm described in the Book in relation to `Key Expansion`, defines `AddRoundKey` like this:
From the given 32-Bytes Cipher Key, I am supposed to generate `4 * (Nr + 1)` ... |
I am having trouble understanding the prime number theorem.
as part of some revision for an exam, I am trying to answer the following questions (but seeing as I don't understand the concept of the prime number theorem... I'm not doing too well):
q1: *what is the proportion of numbers that are prime up to 1,000,00... |
Are the proofs based on a PRF assumption still valid when using a variable-length input PRF ?
The answer is maybe obvious but I have a doubt.
Thank you. |
The most famous text based steganographic scheme is the acrostic: using the first letters of words / sentences. If the mean sentence length is 15-20 words and mean word length is 5 letters, then efficiency is ~1%. You could use shorter than average sentences and/or words to increase the efficiency to within your bounds... |
I am having trouble understanding the prime number theorem.
as part of some revision for an exam, I am trying to answer the following questions (but seeing as I don't understand the concept of the prime number theorem... I'm not doing too well):
q1: *what is the proportion of numbers that are prime up to 1,000,00... |
is `mac = enc(hash(x))` a secure MAC for hash = sha256 and enc AES in cbc mode o ecb mode. Normally aes-cbc is malleable. But in this case i use a hash function for the one-way property. For example, an attacker can:
Change the iv vector:
In `cbc c[0] = enc(m[0] xor iv)`, than an attacker choose `m'[0]` and com... |
I want to partially encrypt a large block of data using AES. meaning given plaintext[0:1100] ,encrypt plaintext[0:1023]. Does this expose what i encrypted to any realistic challenges in the context of my application(copy protection)?
The plaintext is generally machine code, but might have snippets of text. |
What role plays Quantum Fourier Transformation in Shor's integer factorization algorithm? |
I cannot seem to understand the role or goal of Quantum Fourier Transformation in Shor's integer factorization algorithm. Is it used to collapse all quantum states into one, in which it has a factor of a given input $n$? |
Ok, just jumped into crypto and now struggling with some points...
I read lots of resources, most of them mentions about how important the strength of encryption key is.
However, i could not find much info about, what if encryption key is not generated randomly and somehow its fixed or easy guessed? And what if ... |
What if encryption key is not random? |
Some time ago, I asked how to encrypt small messages like e.g., four decimal digit numbers (banking PINs). I've got my answer, but also a warning like it makes no sense as it's easy to guess: Even having no information at all and bad luck implies 10000 trials only, which is nothing in crypto.
However, at an ATM you ... |
I am having trouble understanding the prime number theorem.
As part of some revision for an exam, I am trying to answer the following questions (but seeing as I don't understand the concept of the prime number theorem, I'm not doing too well):
**Question 1:**
What is the proportion of numbers that are prime up... |
I want to partially encrypt a large block of data using AES. Meaning: given `plaintext[0:1100]`, I would like to encrypt `plaintext[0:1023]`. The plaintext is generally machine code, but might have snippets of text.
Does this expose what I encrypted to any realistic challenges in the context of my application (for ... |
Partial encryption of a file? |
Ok, I just jumped into crypto and now struggling with some points…
I read lots of resources, most of them mention how important the strength of the encryption key is. However, I could not find much info about that.
What if the encryption key is not generated randomly and somehow is fixed or easy to be guessed? A... |
What is the security risk if an encryption key is not random? |
Is $mac = enc(hash(x))$ a secure MAC for hash = SHA256 and enc AES in CBC mode or ECB mode. Normally AES-CBC is malleable. But in this case I use a hash function for the one-way property.
For example, an attacker can change the iv vector:
In `CBC c[0] = enc(m[0] ^ iv)` an attacker chooses `m'[0]` and computes `... |
Can I consider my MAC to be a secure MAC? |
Some time ago, I asked how to encrypt small messages like e.g., four decimal digit numbers (banking PINs). I've got my answer, but also a warning like it makes no sense as it's easy to guess: Even having no information at all and bad luck implies 10000 trials only, which is nothing in crypto.
However, at an ATM you ... |
AES 128 requires 10 rounds ( http://en.wikipedia.org/wiki/Advanced_Encryption_Standard#Description_of_the_cipher )
However Bruce Schneier has recommended AES 128 use 16 rounds ( https://www.schneier.com/blog/archives/2011/08/new_attack_on_a_1.html )
Could that be implemented as two full encryptions of AES 128 tha... |
AES 128 requires 10 rounds ( http://en.wikipedia.org/wiki/Advanced_Encryption_Standard#Description_of_the_cipher )
However Bruce Schneier has recommended AES 128 use 16 rounds ( https://www.schneier.com/blog/archives/2011/08/new_attack_on_a_1.html )
Could that be implemented as two full encryptions of AES 128 tha... |
The de-facto answer to any question about increasing the AES rounds is that as yet there doesn't appear to be any need, and any time you do so involves implementing at least some of it in custom code, which is inherently risky.
Throughout this post I'll refer to AES-128 as simply AES.
You certainly wouldn't be ab... |
AES-128 requires 10 rounds ( [AES Description, Wikipedia](http://en.wikipedia.org/wiki/Advanced_Encryption_Standard#Description_of_the_cipher) )
However Bruce Schneier has recommended AES-128 use 16 rounds ( [Schneier on Security: New Attack on AES](https://www.schneier.com/blog/archives/2011/08/new_attack_on_a_1.ht... |
The de-facto answer to any question about increasing the AES rounds is that as yet there doesn't appear to be any need, and any time you do so involves implementing at least some of it in custom code, which is inherently risky.
As far as running AES twice goes, have a look at Meet in the Middle ([MITM][1]) attacks. ... |
Alice publishes (n,e) where n is exponential modulus and e is the public key. We have n=80 digit number and e=3. Bob, in correspondence with Alice, asked Alice to prove she is really Alice, by making her signature on the following five numbers: m1, m2, m3, m4, m5. Then Alice sent 6 numbers, y1, y2, y3, y4, y5, y6 where... |
To answer your last question first, [Triple DES](https://en.wikipedia.org/wiki/Triple_DES) does not need a longer key because it has more rounds than plain DES — rather, Triple DES needs more rounds than plain DES because it has a longer key (and because it aims to offer a security level appropriate for that key ... |
I know that length prepending improves security of CBC-MAC. However, wouldn't inserting the length elsewhere (middle, end or any other part of message) be equally good? After all, even the length is processed by the underlying cipher block. |
What is the difference between the term cipher name like RIJNDAEL and mode of operation like ECB ?
Aren't these both terms represent the encryption/ decryption technique ? |
From DrLecter's commant , i know that DDH problem can be effiently solved with this $$e(g^a,g^b)\stackrel{?}{=} e(g,g^z)$$. i have some trouble to understand this map $e:G \times G \to G_T$. Am i right to understand this to be the "multiplication" of two elements in $Z_p^*$ where $p$ is prime. For example, can $e(U=g... |
What's the definition of non-linearity of a boolean function? Roughly saying it is minimum number of times it equals any affine function. But I don't get it mathematically.
Would you mind helping me? |
In Wikipedia article : [Bent functions](http://en.wikipedia.org/wiki/Bent_function)
there are some figures representing bent functions that are shown here:
![enter image description here][1]
![enter image description here][2]
How does these figures represents a boolean function ?
[1]: https://i.stack.i... |
How this figure represent a boolean function? |
What's the definition of non-linearity of a boolean function? Roughly saying it is minimum number of times it equals any affine function. But I don't get it mathematically.
For example if $f = x_1x_2$ then all affine functions are $g_1 = 0$, $g_1 = x_1$, $g_1 = x_2$ and $g_1 = x_1+x_2$, then non-linearity of $f$ is ... |
Linear functions when expressed as polynomials only have terms of degree 1 or 0. Non-linear functions have at least one term of degree 2 or higher. For example, here is a linear boolean function: $y = ax + bz + c$, where $y$ is the output bit, $x$ and $y$ are input variables, and $a$, $b$, and $c$ are constants. Noti... |
i found a theorem that:
Let $\ MAC = (S,V)$ be a mac for short messages over $\ (K,M,T)$
Let $\ H: M^{big} → M$
Def. $\ MAC^{big} = (S^{big},V^{big})$ over $\ (K,M^{big},T)$ as:
$\ S^{big}(k,m) = S(k,H(m))$ and $\ V^{big}(k,m,t) = V(k,H(m),t)$
**Theorem**. If $\ MAC$ is a secure mac and $\ H$ is collisio... |
Your misunderstanding comes from the fact that often in pairing based crypto there is a "slight" abuse of notation. I will use symmetric pairings in the following for simplicity.
Often one finds $e: G\times G\rightarrow G_T$ be a pairing, the groups $G,G_T$ are of prime order $p$ and $G$ is generated by $g$. This ma... |
In the Wikipedia article "[Bent functions](http://en.wikipedia.org/wiki/Bent_function)",
there are some figures representing those Bent functions:
![image 1 showing the figures][1]
![image 2 showing the figures][2]
How do these figures represent a boolean function ?
[1]: https://i.stack.imgur.com/iqnQt... |
How do these figures represent a boolean function? |
What is the difference between the term cipher name like RIJNDAEL and mode of operation like ECB?
Aren't these both terms represent the encryption/decryption technique ? |
What is the difference between cipher and mode of operation? |
As the topic says, since when can ECC cryptography be freely used?
Isn't it widely used because of patents? There is no alternative to it on embedded devices and smart cards.
Just to mention: I am not from the USA. I'm a simple user who wants ECC to be wide supported. |
What are the advantages of using *"static-ephemeral ECDH"* over *"ephemeral-ephemeral ECDH"*? |
What are the advantages of a static ECDH key? |
I found a theorem that:
Let $\ MAC = (S,V)$ be a mac for short messages over $\ (K,M,T)$
Let $\ H: M^{big} → M$
Def. $\ MAC^{big} = (S^{big},V^{big})$ over $\ (K,M^{big},T)$ as:
$\ S^{big}(k,m) = S(k,H(m))$ and $\ V^{big}(k,m,t) = V(k,H(m),t)$
**Theorem**: If $\ MAC$ is a secure mac and $\ H$ is collisio... |
Proof of secure MAC by hashing a PRF? |
Alice publishes $(n,e)$ where $n$ is exponential modulus and $e$ is the public key. We have $n=80$ digit number and $e=3$. Bob, in correspondence with Alice, asked Alice to prove she is really Alice, by making her signature on the following five numbers: $m1, m2, m3, m4, m5$. Then Alice sent 6 numbers $y1, y2, y3, y4, ... |
I am presently implementing the serpent block cipher in C++ following the specifications. It's important to mention that I'm implementing the cipher in bitslice mode. You'll need the [The full submission package of Serpent][1] which contains the specification of the algorithm and the source code in C and Java.
Lets... |
I know the basic differences between Symmetric vs. Asymmetric cryptography, but I'd love to know more details:
1. Exactly why is the asymmetric approach slower than the symmetric?
2. Why does it make use of longer keys?
3. Why does it require more processing power, etc, etc?
4. In what ways does it trump t... |
I have been reading [Bleichenbacher's 1998 paper][1] on a forged message attack on RSA. The paper assumes access to an Oracle that takes a ciphertext $c$ and will check the decrypted text for valid PKCS #1 padding and returns the validity of the padding. This side-channel can be used for an attack since we can send a f... |
So let any **secure** MAC (message authentication code) be given.
Intuitively, I think it is clear that the probability of getting the same tag on two *different* messages is very small, i.e. negligible. I want to prove this statement mathematically.
How can we
1. formulate this in an exact manner (because, n... |
Moving the conversation further from [here][1] (I couldn't post a comment there because I have no reputation...), I don't think that the question is really answered in depth. I don't really think that encrypting twice with RSA is a waste of time. I think it depends on what is placed in-between the two encryptions (as C... |
Well, let's try it, and see how hard it is to forge a message.
Let's say for illustrative purposes that each character is a block, and that numbers represent the length indicator section. And let's start by putting the length indicator at the end. So,
XXXXXXX7
represents a 7-block message, with the '7' indic... |
What's the definition of non-linearity of a boolean function? Roughly saying it is minimum number of times it equals any affine function. But I don't get it mathematically.
For example, if $f = x_1x_2$, then all the affine functions are $g_1 = 0$, $g_2 = x_1$, $g_3 = x_2$ and $g_4 = x_1+x_2$, then the non-linearity ... |
NIST temporarily closed — will that have a negative impact on the future of cryptography? |
On page 14 of ["Keccak and the SHA-3 Standardization" (February 6, 2013)](http://csrc.nist.gov/groups/ST/hash/sha-3/documents/Keccak-slides-at-NIST.pdf) it says:
> - Instantiation of a sponge function
- the permutation KECCAK-f
- 7 permutations: b → {25,50,100,200,400,800,1600}
- Security-speed trade-of... |
The traditional authenticated DH protocol with PFS against active adversary , ensures that the compromise of both party's long-term private key after the session completed will do no help to the adversary to compute session key, even adversary gets involved in the generation of message. A ID-based key-exchange has some... |
I have been reading [Bleichenbacher's 1998 paper][1] on a forged message attack on RSA. The paper assumes access to an Oracle that takes a ciphertext $c$ and will check the decrypted text for valid PKCS #1 padding and returns the validity of the padding. This side-channel can be used for an attack since we can send a f... |
When implementing cryptographic/coding theory algorithms one need to use data like big prime numbers, numbers in $Z_n$ and their inverses, irreducible polynomials in $Z_n[x]$ and so on...
While sometimes it is easy to write a simple program to get simple examples of these it's handy to have a list with some non-tri... |
I cannot see it having a negative effect, only a positive effect.
Let's look at the [Reddit AMA][1] of Glenn Greenwald and the relevant comment:
> There are **hundreds of encryption standards compromised** by the program the Guardian, NYT and PP all reported on. I have never seen any list of those standards and d... |
My understanding is that a KDF is a function that takes a master secret and generates multiple keys. It is secure as long as the keys are "independent". If this is true, the following definition would generate a secure KDF, right?
> Assuming we have access to a completely random function, $R:
\mathcal{K} \rightarro... |
I do think that in the fullness of time the choice to forcibly migrate people to RC4 will be considered a folly.
We recently had a PCI auditor command that we use RC4 to avoid the BEAST attack. We had no option but to comply or face losing our PCI certification. Across the industry, people are fleeing from AES-CBC ... |
I do think that in the fullness of time the choice to forcibly migrate people to RC4 will be considered a folly.
We recently had a PCI auditor command that we use RC4 to avoid the BEAST attack. We had no option but to comply or face losing our PCI certification. Across the industry, people are fleeing from AES-CBC ... |
I do think that in the fullness of time the choice to forcibly migrate people to RC4 will be considered a folly.
We recently had a PCI auditor command that we use RC4 to avoid the BEAST attack. We had no option but to comply or face losing our PCI certification. Across the industry, people are fleeing from AES-CBC ... |
In my application, I am generating a big random number and publishing a SHA256 hash of it. After the hash it published (but not the secret), anyone can submit any number, and the system will calculate and present them a SHA256 hash of the number derived by concatenating their number at the end of the secret number from... |
How can someone estimate the number of years needed to factor an RSA key based on the advancement of technology if followed Moor's law? |
How can one calculate the estimated RSA key life based on Moor's law? |
I found a theorem that says:
Let $MAC = (S,V)$ be a MAC for short messages over $(K,M,T)$.
Let $H: M^{big} → M$.
Define $MAC^{big} = (S^{big},V^{big})$ over $(K,M^{big},T)$ as:
$S^{big}(k,m) = S(k,H(m))$ and $V^{big}(k,m,t) = V(k,H(m),t)$.
**Theorem**: If $MAC$ is a secure mac and $H$ is a collision-resi... |
Is $mac = enc(hash(x))$ a secure MAC for hash = SHA256 and enc AES in CBC mode or ECB mode. Normally AES-CBC is malleable. But in this case I use a hash function for the one-way property.
For example, an attacker can change the iv vector:
In `CBC c[0] = enc(m[0] ^ iv)` an attacker chooses `m'[0]` and computes `... |
Does encrypting a hash of the message yield a secure MAC? |
Yes, your MAC is secure. It's probably not quite as secure as you're expecting it to be, and it's not a construction I would recommend to anyone, but it should be secure.
----
Let's start with a simpler variant: $F_K(M) = E_K(H(M))$ where $H(\cdot)$ is a 128-bit collision-resistant hash (say, the first 128 bits ... |
It's clear that, as a first pass, Hashcash is in FNP.
For instance, say that R(x,y) is a binary relation, where x is a "maximum" target hash, and y is an input string (working block + nonce), R(x,y) is true iff hash(y) < x. Since SHA256 can be computed in polynomial time, proposed solutions can be checked in polynom... |
What complexity class is Bitcoin's proof-of-work (hashcash) in? |
How can someone estimate the number of years needed to factor an RSA key based on the advancement of technology if followed Moore's law? |
How can one calculate the estimated RSA key life based on Moore's law? |
Let's assume Bob and Alice has a secret key for MAC. If MAC is constructed by the key and the message, that means that both Alice and Bob can construct the exact same message and MAC. So, Bob can claim Alice created certain message, not him. What's the point to use MAC then? Why not just use symmetric encryption? |
Does MAC provide origin authentication? Why not just use symmetric encryption? |
i know that this is not the best use case for RSA, but for a customer of mine i have to encode user data on the server in a way so that it can be decoded/downloaded by the customer through a "secure" webpage.
**Workflow**
Users can register on the page and leave some sensitive data (no credit card data, but age, ... |
How vulnerable is RSA when using it to encode ~1000s of datasets with 500bytes each? How easy can the private key passphrase be hacked? |
Is there a scheme that allows for both of the above? I've tried digging around on the Internet but haven't found anything conclusive on the topic. |
Is there an encyption scheme that combines additive homomorphism with ability to proxy re-encrypt? |
The traditional authenticated DH protocol with PFS against active adversaries, ensures that the compromise of both party's long-term private keys after the session is completed will not help the adversary to compute session key, even adversary gets involved in the generation of messages.
<br>
An ID-based key-exchange... |
i know that this is not the best use case for RSA, but for a customer of mine i have to encode user data on the server in a way so that it can be decoded/downloaded by the customer through a "secure" webpage.
**Workflow**
Users can register on the page and leave some sensitive data (no credit card data, but age, ... |
I know that this is not the best use case for RSA, but for a customer of mine I have to encode user data on the server in a way so that it can be decoded/downloaded by the customer through a "secure" webpage.
**Workflow**
Users can register on the page and leave some sensitive data (no credit card data, but age, ... |
Is there an encyption scheme that combines additive homomorphism with ability to proxy re-encrypt? I've tried digging around on the Internet but haven't found anything conclusive on the topic. |
I'm looking at two curves: Secp 256K1 and P-256. Is there any relationship between the curves such that I can consistently "map" or "project" values from one curve to another?
Is this a good idea? (What faults could crop up when doing so?
My goal is to allow for two independent crypto systems based on ECDSA to ... |
Can Secp 256 K1 curves "map" to a value on P-256? Is that a (un)wise idea? |
Assuming a random number generation process outputs lots of numbers between 0-9. First I gathered up a bunch of the numbers, converted them to binary and created a bitmap.
![enter image description here][1]
Not so random as you can see! That must be why you shouldn't just use raw integers as random numbers in a ... |
Alice has two secret numbers, a and b. She provides c1=E(a), c2=E(b) and c3=E(a+b) to Bob. Is there an encryption system E such that Bob would be able to prove that the c3 as supplied by Alice is actually E(a+b)?
Note that this is different from homomorphic encryption. In case of homomorphic encryption Bob is able t... |
If I've got an LFSR, let's say a 16-bit Fibonacci LFSR as shown in the corresponding [wikipedia article](http://en.wikipedia.org/wiki/Linear_feedback_shift_register), which generates maximum length sequences, could I use it to create word sequences instead of bit sequences?
Staying with the wiki example, let's say I... |
RSA was there first. That's actually enough for explaining its preeminence. RSA was first published in 1978 and the [PKCS#1][1] standard (which explains exactly how RSA should be used, with unambiguous specification of which byte goes where) has been publicly and freely available since 1993. The idea of using elliptic ... |
Alice has two secret numbers, a and b. She publishes c1=E(a), c2=E(b) and c3=E(a+b). Is there an encryption system E such that anyone would be able to prove that the c3 as supplied by Alice is actually E(a+b)?
Note that this is different from homomorphic encryption. In case of homomorphic encryption Bob is able to c... |
Alice has two secret numbers, a and b. She publishes c1=E(a), c2=E(b) and c3=E(a+b). Is there an encryption system E such that anyone would be able to prove that the c3 as published by Alice is actually E(a+b)?
EDIT: Modified the question to use "anyone" instead of "Bob".
Note that this is different from homomorp... |
I'm currently examining the [NaCl library written by Daniel J. Bernstein][1] and I noticed that the library hard codes the sigma:
static const unsigned char sigma[16] = "expand 32-byte k";
In all the salsa stream implementations:
crypto_stream_xsalsa20
crypto_stream_salsa20
crypto_stream_sals... |
I'm currently examining the [NaCl library written by Daniel J. Bernstein][1] and I noticed that the library hard codes the sigma:
static const unsigned char sigma[16] = "expand 32-byte k";
In all the salsa stream implementations:
crypto_stream_xsalsa20
crypto_stream_salsa20
crypto_stream_sals... |
From DrLecter's comment , i know that DDH problem can be effiently solved with this $$e(g^a,g^b)\stackrel{?}{=} e(g,g^z).$$
I have some trouble to understand this map $e:G \times G \to G_T$. Am i right to understand this to be the "multiplication" of two elements in $Z_p^*$ where $p$ is prime. For example, can $e... |
From DrLecter's comment, I know that DDH problem can be efficiently solved with this $$e(g^a,g^b)\stackrel{?}{=} e(g,g^z).$$
I have some trouble to understand this map $e:G \times G \to G_T$. Am I right to understand this to be the "multiplication" of two elements in $Z_p^*$ where $p$ is prime. For example, can $... |
I'm currently examining the [NaCl library written by Daniel J. Bernstein][1] and I noticed that the library hard codes the sigma:
static const unsigned char sigma[16] = "expand 32-byte k";
In all the salsa stream implementations:
crypto_stream_xsalsa20
crypto_stream_salsa20
crypto_stream_sals... |
Why did the MARS cipher receive such a high number of negative votes in the AES competition? As I understand only MARS and Serpent inplement mesures to couter future cryptoanalitic atacs, so it would seem that it is one of the most secure ciphers in the competition. Am I missing something?
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.