instruction stringlengths 15 30k |
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Is there any analysis of freebsd's "geli" encrypted geometry provider? |
Can insecure hash algorithms be combined to form a secure hash algorithm, by concatenating their digests? |
Which of the following protocols is susceptible to replay attack :-
1) A -----> B username, password
2) A -----> B username, h(timestamp,password)
3) A -----> B username timestamp, h(password)
4) A -----> B username, h(timestamp), h(password)
I think the answer is 1 and 3
I know 2) is se... |
How do we arrive to the equation for solving D in RSA? |
de mod phi(n)=1
d = 1/(e mod phi(n).
With having e and n, we can calculate the value of d , the private key for cracking.
Why do people worry about factoring d when this technique is available?
I would like to know some real insight into this.
Edit: d = e^-1 mod phi(n) |
Are you asking "given $e$ and $\phi(n)$, how do we find $d$ such that $de \equiv 1 \bmod \phi(n)$"? (which can also be written as $d = e^{-1} \bmod \phi(n)$
The standard way of find such a value is the [Extended Euclidean Method][1]; this is a relatively efficient method that results in $d$ given $e$ and $\phi(n)$ a... |
I have a third-party point-of-sale API that I am trying to communicate with over HTTP, but I have a problem with it.
In a nutshell, a request is encrypted using RSA, and the response is encrypted using RSA followed by Rijndael/AES-128. The RSA keys are provided by the vendor, the AES IV is a vendor-provided guid, a... |
What is "serial concatenation"? |
I have a third-party point-of-sale API (Speedflow Pay-N-Get) that I am trying to communicate with over HTTP, but I have a problem with it.
In a nutshell, a request is encrypted using RSA, and the response is encrypted using RSA followed by Rijndael/AES-128. The RSA keys are provided by the vendor, the AES IV is a v... |
When encryption is done using the AES-CBC algorithm, the encryption can be thought of as chaining the cipher texts with the previous ones and an IV. However, if its on CBC mode, we give our cipher text forward diffusive properties (i.e. if we change but i in our cipher, plaintext is change for all blocks after that). T... |
I'm looking for a slow keyed trapdoor permutation; or in other words a block cipher $E_K: P\in\{0,1\}^b\mapsto C\in\{0,1\}^b$ with moderate block size $b\approx 64$ bits, wide key $K$, indistinguishable from a random permutation for one not knowing $K$, and additional characteristics:
- encryption $E_K$ is controlla... |
Slow keyed trapdoor permutation? |
So if I understand correctly, the following describes your cipher:
- Take letters A-Z to be numbers 0-25.
- Let M<sub>i</sub> represent letter i of the message
- Let C<sub>i</sub> represent letter i of the ciphertext
- Let n be the ceasar shift number
- Let m be the skip number
- Let the key be described as the... |
In RSA encryption as practiced (that is, to encipher a message which is a short symmetric key), the message size after padding is fixed and equal to the modulus size. Thus the size of the message has no impact on performance.
Calculating a modular inverse is performed only during key generation, that is seldom. Also... |
For $d = e^{-1} \operatorname{mod} \phi(n)$
$$de \operatorname{mod} \phi(n)=1$$
$$d = 1/(e \operatorname{mod} \phi(n))$$
With having $e$ and $n$, we can calculate the value of $d$ , the private key for cracking.
Why do people worry about factoring $d$ when this technique is available?
I would like to know some... |
For $d = e^{-1} \mod \phi(n)$
$$d\cdot e \operatorname{mod} \phi(n)=1$$
$$d = 1/(e \operatorname{mod} \phi(n))$$
With having $e$ and $n$, we can calculate the value of $d$ , the private key for cracking.
Why do people worry about factoring $d$ when this technique is available?
I would like to know some real in... |
Given $n=pq$ for $p,q$ known, I can calculate $\phi(n)$.
$e$ is selected such that $\gcd (e,\phi(n)) = 1$.
Using this, how do I calculate the RSA private key?
------------------
Example:
> I have $n = 35$, with $(p,q)=(5,7)$.
> I have also computed $\phi(n)=24$, and selected $e$ such that $\gcd (e,\phi(n)... |
How do I calculate the private key in RSA? |
The main misconception here is, what part of the RSA problem is actually hard to compute.
Your statement is like this:
- We have $e$ and $n$.
- We know $ed=1$ mod $\phi(n)$.
- So we should be able to calculate $d$.
Your reasoning is exactly what is happening in the key generation algorithm. Division in modul... |
At the time of answering, the question was *can insecure algorithms be combined to form a secure algorithm?*
-----------
**Yes**: Think of any secure round-based block cipher. The independent rounds are not secure, but put together the overall cipher is. I think my favourite example is (currently) the [Even Manso... |
Due to some platform restrictions our decryption can only handle up to 1 million bytes. The string we receive is larger. Is it possible to somehow split the encrypted data and decrypt the parts? |
Is it possible to split a large AES encrypted string and decrypt the parts one by one? |
The main misconception here is, what part of the RSA problem is actually hard to compute.
Your statement is like this:
- We have $e$ and $n$.
- We know $ed=1$ mod $\phi(n)$.
- So we should be able to calculate $d$.
Your reasoning is exactly what is happening in the key generation algorithm. Division in modul... |
Due to some platform restrictions our decryption algorithm can only handle up to 1 million bytes. The string we receive is larger, having been generated by AES in cipher block chaining (CBC) mode, with PKCS5 padding.
Is it possible to somehow split the encrypted data and decrypt the parts? |
I'm looking for a slow <strike>keyed trapdoor</strike> one-way pseudorandom permutation; or in other words a block cipher $E_K: P\in\{0,1\}^b\mapsto C\in\{0,1\}^b$ with moderate block size $b\approx 64$ bits, wide key $K$, indistinguishable from a random permutation for one not knowing $K$, and additional characteristi... |
Slow one-way pseudorandom permutation? |
Can insecure algorithms be combined to form a secure algorithm? |
This is hypothetical as I can't think of any reason to do this, but out of curiosity..
Could I, **for example**, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite broken, but getting close), to form a secure concatenated digest? Intuitively, I would think the chances of finding a c... |
This is hypothetical as I can't think of any reason to do this, but out of curiosity..
Could I, for example, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite broken, but getting close), to form a secure concatenated digest? Intuitively, I would think the chances of finding a colli... |
For example, how would I calculate or tell how many bits of security a secure hash function with 160 bits output would have? Assuming there are no known weaknesses.
Thanks! |
Well, how resistant to attack would depend on what security properties you would need from it.
There are three standard assumptions we can make about a hash function:
- Given a hash value, it is difficult to find an image that hashes to that value; this is known as *preimage resistance*
- Given a image that ha... |
How can I tell how many bits of security a secure hash function has?
For example, how would I calculate or tell how many bits of security a secure hash function with 160 bits output would have? Assuming there are no known weaknesses… |
How can I tell how many bits of security a secure hash function has? |
I was reading some articles about attacks on RSA system and I wonder about some generalization of the following theorem.
> Theorem (Coppersmith).
>
> Let $N=pq$ be an $n$-bit RSA modulus, where
> $p<q<2p$. Then given the $\frac{n}{4}$ least significant bits of $p$
> (that is $\approx$ half of LSB of $p$) or the... |
There are various different [modes of operation](http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation) for block cipher use, some of which provide "encryption" and some of which provide [authenticated encryption](http://en.wikipedia.org/wiki/Authenticated_encryption).
**Why should I use an [authenticated encr... |
Why should I use Authenticated Encryption instead of just encryption? |
For all $c_0\leftarrow m_0 \oplus k$ there exists a $k'$ such that $c_1 \leftarrow m_1 \oplus k'$, where $m_0 \neq m_1$ and $c_0 = c_1$.
Assuming a truly random $k$, the first assignment is a one-time pad. If we were to repeat the process over all $m \in M$, we would create a Stirling set of the first kind.
To ... |
Certainly you _could_ turn your wordlist into a regexp that matches any string of concatenated words, something like:
^(a|aardvark|aardvarks|abaci|aback|...|zucchinis|zygote|zygotes)*$
There even exist tools to optimize such regexps, such as the [Regexp::Assemble](http://search.cpan.org/perldoc?Regexp::Assemb... |
When we transmit information across an insecure channel, we wish for our data to be secure.
So, what does this mean? To discuss these we'll use the standard cryptographic situation of Alice and Bob.
Alice wants to send something (the *plaintext*) across an insecure channel (what this means will be discussed) to Bo... |
When we transmit information across an insecure channel, we wish for our data to be secure.
So, what does this mean? To discuss these we'll use the standard cryptographic situation of Alice and Bob.
Alice wants to send something (the *plaintext*) across an insecure channel (what this means will be discussed) to Bo... |
When we transmit information across an insecure channel, we wish for our data to be secure.
So, what does this mean? To discuss these we'll use the standard cryptographic situation of Alice and Bob.
Alice wants to send something (the *plaintext*) across an insecure channel (what this means will be discussed) to Bo... |
When we transmit information across an insecure channel, we wish for our data to be secure.
So, what does this mean? To discuss these we'll use the standard cryptographic situation of Alice and Bob.
Alice wants to send something (the *plaintext*) across an insecure channel (what this means will be discussed) to Bo... |
What I want to do is use asymmetric crypto to guarantee that a file comes from a source. I have software that runs on lots of wireless devices, and each of those has a license file with an encrypted date that they expire. I'd like to be able to encrypt it in the office and have the devices decrypt/read the date. The pu... |
Quite a difficult question. What you seem to need is a one-way permutation $P$. Indeed, suppose you have it of width $d$, then consider the function
$$
F(K,S,R_S) = E_{K_2}(P(E_{K_1}(S,R_S))),
$$
where $E$ is any good 64-bit block cipher (say, [Simon][1]) and $K_1,K_2$ are derived from $K$. This function $F$ shoul... |
Suppose you are running a server with the Diffie-Hellman parameters (so the group `G` and generator `g`) generated once. There are many connections made to the server, all using TLS with an DHE cipher suite.
Now, assume an adversary captures all connections and is able to break one key exchange (find the master key)... |
How well does breaking multiple DH key exchanges over the same group scale? |
What, exactly, are your trying to accomplish with this construction?
Yes, you're correct in that, given a sequence of messages $m_0, m_1, m_2, \dotsc$ and a fixed ciphertext $c$ (assumed to be all of the same length), we can easily calculate a sequence of keys $k_i = c \oplus m_i$ such that $k_i \oplus m_i = c$.
... |
Certainly you _could_ turn your wordlist into a regexp that matches any string of concatenated words, something like:
^(a|aardvark|aardvarks|abaci|aback|...|zucchinis|zygote|zygotes)*$
There even exist tools to optimize such regexps, such as the [Regexp::Assemble](http://search.cpan.org/perldoc?Regexp::Assemb... |
why RSA uses Semiprime numbers? why not just use any big number ??
What is the advantage of the two original numbers being prime?
Because factoring any big number will be difficult |
why RSA uses Semiprime numbers? |
Why does RSA use semiprime numbers? Why not just use any big number ??
<br>
What is the advantage of the two original numbers being prime?
Because factoring any big number will be difficult |
For $d = e^{-1} \mod \phi(n)$
$$d\cdot e \operatorname{mod} \phi(n)=1$$
$$d = (e^{-1} \operatorname{mod} \phi(n))$$
With having $e$ and $n$, we can calculate the value of $d$ , the private key for cracking.
Why do people worry about factoring $d$ when this technique is available?
I would like to know some real... |
I've been given as an exercise to show an encryption scheme that is CCA-secure but is not a secure message transmission scheme.
What is message transmission scheme?
How does it differ from just an encryption scheme? |
What is Message Transmission Scheme? |
I've been given as an exercise to show an encryption scheme that is CCA-secure but is not a secure message transmission scheme.
What is a message transmission scheme, and how does it differ from a regular encryption scheme? |
What is a Message Transmission Scheme? |
The crucial difference between plain encryption and authenticated encryption (AE) is that AE additionally provides authenticity, while plain encryption provides only confidentiality. Let's investigate in detail these two notions.
In the further text, we assume $K$ to be a secret key, which is known to authorized par... |
I'm now studying the DES construction and realized that it uses several small PRPs instead a big one for saving memory.
Why does the PRP with input/output of $n$ bits utilize $log(2^n!)$ memory?
I thought it should utilize $n\cdot2^n$. |
My understanding is crypto researchers tend to prefer solving a problem in software without the need for secure hardware. Why is this? What is the big problem with using secure hardware if the hardware components are cheap and can be easily made? |
Why is it that researchers prefer finding secure software solutions over secure hardware solutions? |
The crucial difference between plain encryption and authenticated encryption (AE) is that AE additionally provides authenticity, while plain encryption provides only confidentiality. Let's investigate in detail these two notions.
In the further text, we assume $K$ to be a secret key, which is known to authorized par... |
I have the following Ciphertext: TXFOXEVXHSFCGAQKZ and the plaintext: It takes two to Tango. is it possible to know the key? if not, what do I need to find it? |
I have the following ciphertext: "TXFOXEVXHSFCGAQKZ" and the plaintext: "It takes two to Tango". Is it possible to know the key? If not, what do I need to find it? |
I have the ciphertext and the plaintext. Is it possible to know the key? If not, what do I need to find it? |
I think this question is setting up a false dichotomy.
It's not that a researcher has an opinion as to whether they prefer software or hardware implementations. The choice of implementation depends on the requirements of the specific cryptosystem you're building.
For example, if you're designing a system to encr... |
Each one of your first two sentences has a mistaken premise: you're starting from some assumptions that aren't actually true.
DES does not use small PRPs for saving memory. It doesn't use small PRPs at all. The DES S-boxes are not PRPs. The DES F-function is not a PRP.
A PRP does not necessarily require $\lg(2... |
I'm now studying the block cipher - SPN construction and realized that it uses several small PRPs instead a big one for saving memory (or that is one of the reasons).
Why does the PRP with input/output of $n$ bits utilize $log(2^n!)$ memory? (When saving a full table of $domain->range$)
I thought it should utiliz... |
I'm struggling some DES variant that I got as an exercise (exercise taken from Katz-Lindell Ex5.14).
The variant is as follows:
The left half of the master key is used to derive all the sub-keys in rounds 1-8, while the right half of the master key is used to derive all the sub-keys in rounds 9-16.
**My direc... |
I'm struggling with some DES variant that I got as an exercise (exercise taken from Katz-Lindell Ex5.14).
**The variant is as follows:**
The left half of the master key is used to derive all the sub-keys in rounds 1-8, while the right half of the master key is used to derive all the sub-keys in rounds 9-16.
*... |
Can you help me with this DES variant analysis? |
Each one of your first two sentences has a mistaken premise: you're starting from some assumptions that aren't actually true.
DES does not use small PRPs for saving memory. It doesn't use small PRPs at all. The DES S-boxes are not PRPs. The DES F-function is not a PRP. A SPN does not use several small PRPs for s... |
First time using LaTeX, apologies if a bit of a mess!
Encryption : $\ f_{N,e} : Z^{*}_{N} \rightarrow QR(N)^{*}; x \rightarrow x ^{2e} mod N$
I need to show that for $\ x_{0} \in Z^{*}_{N} $ there are four elements$\ x \in Z^{*}_{N}$ such that $\ f_{N,e}(x) = f_{N,e}(x_{0})$
This seems like a cross between R... |
Rabin/RSA four possible messages? |
I once asked a question ["Would RSA make sense if we used no computers?"][1]. The answer was negative, because finding primes that would make secure keys would prove too hard. Assuming that we had found another way of finding primes without computers, would RSA be usable in, for example, medieval times?
[1]: http:... |
Assuming that we had a way of finding primes, could RSA be used without computers? |
Given this encryption method:
$$f_{N,e} : Z^{*}_{N} \to QR(N)^{*};\quad f_{N,e}(x) = x ^{2e} \bmod N$$
I need to show that, for any $x_{0} \in Z^{*}_{N}$, there are four elements $x \in Z^{*}_{N}$ such that $f_{N,e}(x) = f_{N,e}(x_{0})$.
This seems like a cross between RSA ($x \mapsto x^{e} \bmod N$) and Rabin... |
I read [Cryptographic sponge functions][1] paper, but I'm still confused.
Is ciphertext absorbed or plaintext?
[1]: http://sponge.noekeon.org/CSF-0.1.pdf |
How does this happen in RSA malleability? |
I don't understand how the E(m) turns into (mt). I mean, I don't know how does that transformation happen and how does the equation occur.
![enter image description here][1]
[1]: https://i.stack.imgur.com/k5Rvi.png
See, E(m) is m^e mod n, so if you plug in real values, it won't work.
For example, c1 = ... |
I don't understand how the E(m) turns into (mt). I mean, I don't know how does that transformation happen and how does the equation occur.
![enter image description here][1]
[1]: https://i.stack.imgur.com/k5Rvi.png
See, E(m) is m^e mod n, so if you plug in real values, it won't work.
For example, c1 = ... |
I don't understand how the $E(m)$ turns into $(mt)$. I mean, I don't know how does that transformation happen and how does the equation occur.
$E(m) • t^e \mod n = (mt)^e \mod n = E(mt)$
See, $E(m)$ is $m^e \mod n$, so if you plug in real values, it won't work.
For example:
c1 = 17^23 mod 35
c2 = ... |
I have been reading the [Cryptographic sponge functions][1] paper, but I'm still confused.
Is ciphertext absorbed or plaintext?
[1]: http://sponge.noekeon.org/CSF-0.1.pdf |
Does Keccak absorb ciphertext or plaintext? |
Can you explain “weak keys” for DES? |
Did you try [Wikipedia](https://en.wikipedia.org/wiki/Weak_key#Weak_keys_in_DES)?
DES consists of 16 rounds of the form:
$$L_{i+1} = R_{i}, \quad R_{i+1} = L_i \oplus F(R_i, K_i),$$
which are identical except for the round subkeys $K_i$. (The last round is slightly different, in that the half-blocks $L$ and $... |
Did you try [Wikipedia](https://en.wikipedia.org/wiki/Weak_key#Weak_keys_in_DES)?
DES consists of 16 rounds of the form:
$$L_{i+1} = R_{i}, \quad R_{i+1} = L_i \oplus F(R_i, K_i),$$
which are identical except for the round subkeys $K_i$. (The last round is slightly different, in that the half-blocks $L$ and $... |
I have a third-party point-of-sale API (Speedflow Pay-N-Get) that I am trying to communicate with over HTTP, but I have a problem with it.
In a nutshell, a request is encrypted using RSA, and the response is encrypted using RSA followed by Rijndael/AES-128. The RSA keys are provided by the vendor, the AES IV is a v... |
I don't understand how the $E(m)$ turns into $(mt)$. I mean, I don't know how does that transformation happen and how does the equation occur.
$$E(m) \cdot t^e \bmod n = (mt)^e \bmod n = E(mt)$$
See, $E(m)$ is $m^e \bmod n$, so if you plug in real values, it won't work.
For example:
* $c_1 = 17^{23} \bmod ... |
I am considering the FNV1a 32 bit hash as part of a simple software security and authentication system. I am aware that FNV1a is NOT ideal but it may suit my needs.
I am aware that FNV1a has rather poor collision behavior, but I would like to know if it may be implemented in such a way as to minimize problems. Assum... |
First of all, _"Is collision less likely for individual characters than for strings?"_
The answer to this is __yes__. In fact, experimentally verifying shows that for 8-bit ASCII characters the collision chance with FNV1a is 0. This is however not an impressive feat, seeing that the output is 4 times as large as the... |
I think this question is setting up a false dichotomy.
It's not that a researcher has an opinion as to whether they prefer software or hardware implementations. The choice of implementation depends on the requirements of the specific cryptosystem you're building.
For example, if you're designing a system to encr... |
I have been reading the [Cryptographic sponge functions][1] paper, but I'm still confused.
Does Keccak in authenticated encryption mode absorb ciphertext or plaintext?
**Edit:** Are there any test vectors to verify implementation of Keccak authenticated encryption?
[1]: http://sponge.noekeon.org/CSF-0.1.pd... |
I don't understand how the $E(m)$ turns into $E(mt)$. I mean, I don't know how does that transformation happen and how does the equation occur.
$$E(m) \cdot t^e \bmod n = (mt)^e \bmod n = E(mt)$$
See, $E(m)$ is $m^e \bmod n$, so if you plug in real values, it won't work.
For example:
* $c_1 = 17^{23} \bmod... |
Does SpongeWrap (from the Keccak team) absorb ciphertext or plaintext? |
I just find this pencil and paper cipher 'Felix' and I want to know how secure it is?
**EDIT**
From http://web.archive.org/web/20110825142054/http://topcat.hypermart.net/papers/felix.txt
> Felix a pencil-and-paper cipher
> I. Synopsis
> Felix is a `pencil-and-paper cipher' offering relatively good se... |
This is probably not secure enough for a proof of work. I'll outline some attacks, of increasing sophistication/complexity and increasing effectiveness (decreasing runtime).
## Brute force ##
The obvious attack is brute force: enumerate all $2^{32}$ possible inputs and check to find the first that produces the d... |
Is there a best practice for Diffie-Hellman parameters (p, g, and q) used on a web server?
The server is using ephemeral keys, but should the parameters be rotated on a regular basis? Is it OK for the server to keep them fixed for years (in the source code)? Or should they be generated uniquely for each site?
Thi... |
The main difficulty in designing what I asked, is coming up with a permutation over a relatively small set, that is easy to compute in the forward direction, but convincingly much more difficult to invert. The least unsatisfactory I have so far is based on the discrete logarithm problem in $\mathbb Z_p$. If $p$ and $(p... |
I'm now studying the block cipher [substitution-permutation network](http://en.wikipedia.org/wiki/Substitution-permutation_network) construction and realized that it uses several small pseudo-random permutations instead a big one for saving memory (or that is one of the reasons).
Why does the PRP with input/output o... |
Many of the beginner explanations use very simple examples:
[like this](http://pajhome.org.uk/crypt/rsa/rsa.html)
It is still hard to factorize a small number by hand, compared to other operations. There is definitely a size of prime numbers where hand computation is still feasible, but hand factorizing isn't. Woul... |
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