instruction stringlengths 15 30k |
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From my understanding man-in-the middle attack works as follow:
Alice and Bob agreed to use Diffie-Hellman using $a$ and $q$. Alice sends $Y_A$. Before it reaches Bob,
Charlie intercepts it and sends $Y_{C1}$ instead. Bob believes to have agreed on a key $K_B$ with Alice, but
the key is actually only shared by Bo... |
What is difference between meet in the middle attack and man in the middle attack? |
i would like to know your view about the title, encrypting a plain text with an affine cipher then encrypting that cryptatext once more using the same cipher but of course different keys. Would it be more secure?
for me it won't, it still can be brute force, that's what i think and i have read about a [vigenere over a... |
Book cipher works this way :
1. Choose a reference book.
2. For each word find its position in the book.
3. replace each word by its coordinates (ie: 2,3,4 = page 2, 3rd line, 4th word).
How would somebody go about cracking a book cipher without the knowing what the key [or book used in this case] is?
Find... |
Can a book cipher be cracked without key? |
I would like to know your view about the title, encrypting a plain text with an affine cipher then encrypting that ciphertext once more using the same cipher, but of course different keys. Would it be more secure?
For me it won't, it still can be brute force, that's what I think and I have read about [Vigenere over ... |
This question has many problems in the way it was asked, and clearly did not come after doing some investigation. However, since this seems to be a misconception that is spreading widely, I will relate to it.
It is *not* true that the "crypto community" (whoever that is) believes that the NSA can break RSA. In fact,... |
Book cipher works this way :
1. Choose a reference book.
2. For each word find its position in the book.
3. replace each word by its coordinates (ie: 2,3,4 = page 2, 3rd line, 4th word).
How would somebody go about cracking a book cipher without the knowing what the key [or book used in this case] is?
Find... |
Assume a user U and a server S. User uploads its data and wants later to perform an authenticity check. It also sends a merklee tree to the server. Lets say we would like the user to ask for a specific element in the tree. The server then returns the leaf node and the path to the root that would allow U to verify. This... |
Let us assume the following scenario: I have just found a way to crack AES-128 in a reasonable time (1-2 days).
How do I publish and prove this? I remember reading about lots of people who cracked DES and other ciphers but how did they publish their work? |
I'm reading a paper based on Homomorphic Encryption: “[Fully Homomorphic Encryption over the Integers: From Theory to Practice](https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201407fa5.pdf)” (PDF).
Now, I need a diagram of this algorithm if possible with all the operation that the sender of cyber tex... |
I am reading this paper "Toward Secure Multikeyword Top-k Retrieval over Encrypted Cloud Data" (http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6425381&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F8858%2F4358699%2F06425381.pdf%3Farnumber%3D6425381).
I am trying to work out an example of the FHEI scheme mentio... |
Example of FHEI scheme? |
I am studying about RO model and just got this question that what are the factors that make it not possible to instantiate a RO with a Hash function. To give a reference on how far I have know about them and other specification, I've followed this [series of blog][1] posts, so far. So, e.g. I know that one factor is th... |
I am developing a simple web app that uses asymmetric encryption, but I am not sure whether to chose RSA for the reasons mentioned above.
What are your suggestions? Also if I decided to go with RSA what is the recommended Key Size ?
Also, someone in the comment area mentioned using libraries made by others, but ... |
I am reading this paper [Toward Secure Multikeyword Top-k Retrieval over Encrypted Cloud Data][1].
I am trying to work out an example of the FHEI (Fully homomorphic Encryption over Integers) scheme mentioned on the paper, but unable to prove it. Can anyone explain the scheme with a working example?
[1]: http:... |
I am studying about RO model and just got this question that what are the factors that make it not possible to instantiate a RO with a Hash function. To give a reference on how far I know about them and other specification, I've followed this [series of blog][1] posts, so far. So, e.g. I know that one factor is that a ... |
So ever since I first took a stab at understanding stream Ciphers, not one stood out more than [RC4][1], because it's so fantastically simple. As most people reading this will know, with it's fantastic simplicity comes with easily done cryptanalysis and RC4 has certainly been subject to plenty of it (leading to RC4's t... |
Can somebody help me understand RC4 Spritz? (A few questions) |
Suppose we have a (variable-input size) hash function modeled as a random oracle. Can it be consistent to say that the time to evaluate this function depends on the input size ? |
So ever since I first took a stab at understanding stream Ciphers, not one stood out more than [RC4][1], because it's so fantastically simple. As most people reading this will know, with its fantastic simplicity comes with easily done cryptanalysis and RC4 has certainly been subject to plenty of it (leading to RC4's to... |
Well the idea of a cryptographically secure hash function (and often functions within them), is to mimic the Random Oracle model as closely as we can. Now, short of a little gremlin (perhaps?), some perfectly unbiased dice, a magical orb and a magic way to store all the possible outcomes from each input, we need these ... |
Well the idea of a cryptographically secure hash function (and often functions within them), is to mimic the Random Oracle model as closely as we can. Now, short of a little gremlin (perhaps?), some perfectly unbiased dice, a magical orb and a magic way to store all the possible outcomes from each input, we need these ... |
I'm working on a short story taking place in the near future in which a hacker gains access to the DARPA mainframe and files related to a highly classified DARPA project.
Being ignorant about state of the art cryptanalysis techniques, is it safe to say it would be virtually impossible to decipher encrypted DARPA fi... |
What is the default algorithm used by the MIRACL-Library [1] for elliptic curve cryptography systems to perform scalar-point multiplication with curves of Weierstrass form satisfying the equation : $y^2 \equiv x^3 + a\cdot x + b \pmod p$ defined over a prime Field $\mathbb{F}_p$ ?
I can't find any satisfying inform... |
I'm writing a project on the advantages and disadvantages of symmetric vs asymmetric cryptosystems. At the moment I am trying to define both systems using mathematical notation. Under the heading "Basic Cryptosystems" I have this:
>We can define the cryptogram functionally as
\begin{equation}
\mathit{C=f(M,K)}
\e... |
Well the idea of a cryptographically secure hash function (and often functions within them), is to mimic the Random Oracle model as closely as we can. Now, short of a little gremlin (perhaps?), some perfectly unbiased dice, a magical orb and a magic way to store all the possible outcomes from each input, we need these ... |
Libsodium has some [helpers](https://download.libsodium.org/doc/helpers/index.html), which allow [hexdecimal decoding](https://paragonie.com/book/pecl-libsodium/read/03-utilities-helpers.md#bin2hex), encoding and also constant-time string comparison.
So if you use the php binding `libsodium-php` you obviously also h... |
Are there any disadvantages of using libsodiums helpers for en-/decoding/comparision instead of the native ones? |
I recently discovered the benaloh cryptosystem.
I am working with the system as it is discribed in the following link:
https://en.wikipedia.org/wiki/Benaloh_cryptosystem
However I need some help in order to understand why we need
\begin{equation}
{gcd(r,(p-1)/r)}
\end{equation}
As far as I understand the co... |
I am planning to build temperature sensor nodes for my home heater control. Central device will control the heater using temperature data read by nodes. These nodes will send temperature data to central device over RF communication periodically. There will be no acknowledge from central device to nodes. I want to learn... |
Following scenario:
We are using OTR for communication between Alice and Bob which means after each successfull message exchange a re-keying happens for both parties leading to new AES-keys for the encryption and MAC generation.
Lets say Alice and Bob exchange 1000 message-pairs which leads to 1000 re-keying occurr... |
Does frequent key change weaken encryption? |
My understanding of the cryptanalysis of AES, is based on what I've read on Wikipedia and my intuition, I have nothing but self-taught education on the subject.
So I want you to imagine: I have only TWO blocks of 128-bit cipher text.
The input was 256bits, we did not use any padding, we also ignored IVs and Salt... |
Practical attack on inpractical implementation of Rijndael (AES?) |
What 'container' is used normally to store/transport secret keys (for symmetric algorithms)?
I have come across PKCS12 format where a public key certificate as well as a private key can be bundled together and stored in an archived file format.
Similarly how can an array of random bytes that can be used as a secr... |
I'm reading a paper based on Homomorphic Encryption: “[Fully Homomorphic Encryption over the Integers: From Theory to Practice](https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201407fa5.pdf)” (PDF).
Now, I need a diagram of this algorithm if possible with all the operation that the sender of cyber tex... |
There are many sources presenting the test vectors.
But you can also extract it from sourcecode implementations as [opencores.org](http://opencores.org/websvn,filedetails?repname=present&path=%2Fpresent%2Ftrunk%2FDecode%2Fbench%2Fvhdl%2FPresentFullDecoderTB.vhd) et al offer them…
> Plaintext: 00000000000000... |
So ever since I first took a stab at understanding stream Ciphers, not one stood out more than [RC4][1], because it's so fantastically simple. As most people reading this will know, with its fantastic simplicity comes with easily done cryptanalysis and RC4 has certainly been subject to plenty of it (leading to RC4's to... |
Can somebody help me understand RC4 Spritz? (Three Questions) |
So ever since I first took a stab at understanding stream Ciphers, not one stood out more than [RC4][1], because it's so fantastically simple. As most people reading this will know, with its fantastic simplicity comes with easily done cryptanalysis and RC4 has certainly been subject to plenty of it (leading to RC4's to... |
My understanding of the cryptanalysis of AES, is based on what I've read on Wikipedia and my intuition, I have nothing but self-taught education on the subject.
So I want you to imagine: I have only TWO blocks of 128-bit cipher text.
The input was 256bits, we did not use any padding, we also ignored IVs and Salt... |
Practical attack on an impractical implementation of Rijndael (AES?) |
Does there exist any sorts of algebraic relationship between Original and Sub Key of DES? I understand that by solving K-Maps of 64-bit Input/48-bit Output, I can get 16 algebraic relationships relating each sub key with the original key. Has someone done it already? Can this be of any use in exploiting the vulnerabili... |
As far as my understanding goes MACs are used to determine whether the received message comes from a source that has access to a MAC-key which is known by both parties.
Some crypto protocols reveal their used MAC keys after having used them up for message-exchange (e.g. OTR).
Explanations (I read) often say that re... |
Why reveal MAC-keys after using them? |
What you're describing is a ciphertext-only attack on AES.<br>
**No, there's no (known) ciphertext-only attack on AES.**
> **Condition one**: We know none of the weaknesses and similar plain-texts
> in these two blocks, I just mentioned, how easily could we discover
> it?
By the lack of an transmitted IV, an a... |
Are they any advantages in using proprietary encryption? |
I need a PRF for use with PBKDF2, however, the only thing I have is the AES block cipher primitive. I'm attempting to derive a keyed hash function from the block cipher. The design is based on the Merkle–Damgård construction. The inputs are $i$ and $k$, for the input data and key, both are a list a bytes. The byte 0xff... |
Is this a secure keyed hashing construction? |
If your data is a set $S$ of key-value pairs, such that $S = \{(k,v) \vert k \in K, v \in V\}$, you can have non-membership proofs for your data by using a _sorted_ Merkle tree (sorted by the keys in $K$).
This tree can be a binary-search tree, a trie, a sparse Merkle Tree (similar to the one in Micali's Zero Knowl... |
I am implementing a hierarchical key system with a randomly generated master key and many randomly generated data keys that should be encrypted using the master key. I am wondering what the best way to encrypt the data keys using the master key is. I am thinking that if I XOR the master key with the data key, that shou... |
If your data is a set $S$ of key-value pairs, such that $S = \{(k,v) \vert k \in K, v \in V\}$, you can have non-membership proofs for your data by using a _sorted_ Merkle tree (sorted by the keys in $K$).
This tree can be a binary-search tree, a trie, a sparse Merkle Tree (similar to the one in Micali's Zero Knowl... |
Are you implementing this for cryptographic purpose ? If so, you should use True Random Number Generators (TRNGs) to generate your master key.Your key should have following properties:
1. Statistical independence = For a given generated sequence of values, a particular value should not be more likely to appear nex... |
I already know *AES* produces a "random" output.
`5e4e6440826d6afc4535fbf078455f791159701a9df624ddd4e4dda84523b6a7`
Its cipher-text doesn't follow a pattern and is indistinguishable from noise.
Is this common in most cipher-texts?
What are some other (specifically fast) examples of ciphers? |
Which ciphers produce random cipher text? |
I can think of only one answer: DRM.
Or rather, anywhere you have a system in which the consumer *must* be able to decrypt and consume the encrypted data in a controlled fashion, but *at the same time* must not be able to do so freely.
Consider, as an example, a 2D game with user-provided content, where users can... |
I already know *AES* produces a "random" output.
`5e4e6440826d6afc4535fbf078455f791159701a9df624ddd4e4dda84523b6a7`
Its ciphertext doesn't follow a pattern and is indistinguishable from noise.
Is this common in most ciphertexts? |
Which ciphers produce random ciphertext? |
Are there any advantages in using proprietary encryption? |
Assume I want to design a protocol (or data format or similar) including some cryptographic hash, and want it to be as future-proof as possible, i.e. I want to avoid that breakthroughs in cryptography make my old data insecure.
If I use only one hash algorithm, I can have bad luck to pick just the one which will be ... |
What is the currently most efficient (interactive) zero knowledge proof/argument for the subset sum problem?
The most recent relevant paper I have found is [Efficient Modular NIZK Arguments from Shift and Product - Prastudy Fauzi, Helger Lipmaa, Bingsheng Zhang](https://eprint.iacr.org/2012/548), but it considers NI... |
I already know *AES* produces a "random" output.
`5e4e6440826d6afc4535fbf078455f791159701a9df624ddd4e4dda84523b6a7`
Its ciphertext doesn't follow a pattern and is indistinguishable from noise.
Is this common for most ciphers? |
Simple question, what are the limitations of ECC, both in terms of application and how secure it is?
I heard that the NSA were able to read emails a few years back due to a backdoor they had discovered on a particular NIST elliptic curve. Is this something we can continue to expect, and what other potential drawback... |
Limitations of Elliptic Curve Cryptography? |
Consider the following function:
$f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e~mod~n$,
where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public RSA exponent) with $\varphi(n) = (p-1)\cdot (q-1)$.
How can the cardinality of $Y$ be computed or estimated (in terms... |
Consider the following function:
$f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e \bmod n$,
where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public RSA exponent) with $\varphi(n) = (p-1)\cdot (q-1)$.
How can the cardinality of $Y$ be computed or estimated (in ter... |
This is a rather open ended question, but I'll try to answer:
Limitations:
- ECDSA requires a secure random generator - if the same random value is reused (for different plaintext) then the private key parameter can simply be calculated;
- ECDSA requires a hash function and cannot be (easily?) used for signatu... |
This is a rather open ended question, but I'll try to answer:
Limitations:
- most ECDSA implementations require a secure random generator - if the same random value is reused (for different plaintext) then the private key parameter can simply be calculated;
- ECDSA requires a hash function and cannot be (easil... |
This is a rather open ended question, but I'll try to answer:
Limitations:
- most ECDSA implementations require a secure random generator - if the same random value is reused (for different plaintext) then the private key parameter can simply be calculated;
- ECDSA requires a hash function and cannot be (easil... |
> Consider the following function:
> $f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e \bmod n$,
> where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public RSA exponent) with $\varphi(n) = (p-1)\cdot (q-1)$.
> How can the cardinality of $Y$ be computed or estimated... |
Consider the following function:
$f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e \bmod n$,
where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public RSA exponent) with $\varphi(n) = (p-1)\cdot (q-1)$.
How can the cardinality of $Y$ be computed or estimated (in ter... |
On the section 4.2, page 10, of the paper [Order-Preserving Symmetric Encryption][1], the authors define two subroutines: the first one is called $HGD$ and the second one is $GetCoins$.
I have doubts about both, but I am mainly interested on the first.
It is said that
> The first, denoted $HGD$, takes inputs ... |
> $p$ is a large prime number. Consider the following function $F:\mathbb Z^*_p \times \mathbb D\rightarrow\mathbb Z^*_p$ where $\mathbb D=2,....,p-1$.
> $F_k(x)=x^k \bmod p$
> Proof that it's not a secure pseudorandom function.
**What I‘ve tried:**
I give a value to $x_1$ and obtein $y_1$, then I set $x_2... |
I want to calculate the hamming weight of a S-Box using this formula:
$\text{hw}(f) = \sum_{x=0}^{2^n-1} f(x)$.
Where $f: \{0, 1\}^n \rightarrow \{0, 1\}$
My problem is that I don't know how to geht the $f$-function.
I found a helpful paper at:
https://sdsu-dspace.calstate.edu/bitstream/handle/10211.10/448/C... |
I think the keyword equality can be done with FHE, but, as you pointed out, the server will not know the result of the test since it will be encrypted.
Considering this, the answer to your question "Does this mean server does not know whether the string matches the document?" should be *yes, it does. The server does... |
I want to calculate the hamming weight of a S-Box using this formula:
$\text{hw}(f) = \sum_{x=0}^{2^n-1} f(x)$.
Where $f: \{0, 1\}^n \rightarrow \{0, 1\}$
My problem is that I don't know how to get the $f$-function.
I found that helpful paper: [THE DESIGN OF S-BOXES][1]. At Page 9 (18) boolean functions are d... |
I would like to learn more about a specific set of invertible functions:
The function should accept 2 inputs: one hidden and the other visible.
The output and the function should also be visible.
The hidden input will not change, the visible will.
The function should be deterministic. Collisions are acceptabl... |
I would like to learn more about a specific set of non invertible functions:
The function should accept 2 inputs: one hidden and the other visible.
The output and the function should also be visible.
The hidden input will not change, the visible will.
The function should be deterministic. Collisions are accep... |
I want to calculate the hamming weight of a S-Box using this formula:
$\text{hw}(f) = \sum_{x=0}^{2^n-1} f(x)$.
Where $f: \{0, 1\}^n \rightarrow \{0, 1\}$
My problem is that I don't know how to get the $f$-function.
I found that helpful paper: [THE DESIGN OF S-BOXES][1]. At Page 9 (18) boolean functions are d... |
I would like to learn more about a specific set of non invertible functions:
- The function should accept 2 inputs: one hidden and the other visible.
The output and the function should also be visible.
- The hidden input will not change, the visible will.
- The function should be deterministic. Collisions are acc... |
Name and security of these non-invertible functions? |
I have some hash function representations, which I find it hard to understand.
I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations given below:
Choose cryptographic hash functions
H1:{0, 1}∗×Z ∗p → Z ∗q ,
H2:{0, 1}∗×Z ∗p ×Z ∗p → Z ∗q ,
H3:{... |
In the context of SSL/TLS protocol and [SLOTH][1] vulnerability. I want to find out if certain websites(webservers) or applications that use TLS are vulnerable. I need some guidance for this.
My idea is to develop/find a tool(maybe openssl) that connects to the servers and in the client hello asks for RSA-MD5 Signa... |
While looking at the different versions of OTR protocol I discovered a strange thing: there is no trace of the patch for the weaknesses that were noted in [this][1] research.
It sounds very strange to me that authors of [OTRv2][2] and [OTRv3][3] did not managed to patch up the weaknesses and did not even bother to m... |
I have some hash function representations, which I find it hard to understand.
I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations given below:
Choose cryptographic hash functions
<tex>
$H_1:\{0, 1\}^*× Z^∗_p → Z^∗_q$,
$H_2:\{0, 1\}^∗×Z^∗_p ×... |
I have some hash function representations, which I find it hard to understand.
I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations given below:
> Choose cryptographic hash functions
$H_1:\{0, 1\}^*× Z^∗_p → Z^∗_q$,
$H_2:\{0, 1\}^∗×Z^∗_p ×Z^∗_p... |
I have some hash function representations, which I find it hard to understand.
I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations given below:
> Choose cryptographic hash functions<br>
$H_1:\{0, 1\}^*× Z^∗_p → Z^∗_q$,
$H_2:\{0, 1\}^∗×Z^∗_p ×Z^... |
I have some hash function representations, which I find it hard to understand.
I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations given below:
> Choose cryptographic hash functions<br>
$H_1:\{0, 1\}^*\times\mathbb Z^∗_p\to\mathbb Z^∗_q$<br>
$H_2... |
[![4 x E = D in Simplified AES how it's possible ??][1]][1]
Can anyone explain how it's possible through hexadecimal or Binary 4 x E= D
[1]: https://i.stack.imgur.com/ZH0hb.png |
4 x E = D in Simplified AES how it's possible ?? |
Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different primitives)?
For instance, Whit Diffie is on record as saying that he originally much preferred RSA because it provided signa... |
Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different primitives)?
For instance, Whit Diffie is on record as saying that he originally much preferred RSA because it provided signa... |
I have a hardware engine for SHA256,which can process 64K of data but the input data size,i am getting is around 1MB. what should i do to process 1MB size.
what should be my input after 1st 64KB and what will be my IV(initial vector)??
Can anyone give any idea?
Thanks in advance |
I have a hardware engine for SHA256 which can process 64K of data, but the input data size I am getting is around 1MB. What should I do to process 1MB size.
What should be my input after 1st 64KB and what will be my IV (initial vector)?
Can anyone give any idea? |
I have a hardware engine for SHA256 which can process 64K of data, but the input data size I am getting is around 1MB. What should I do to process 1MB size.
What should be my input after 1st 64KB and what will be my IV (initial vector)?
Can anyone provide any idea? |
While looking at the different versions of OTR protocol I discovered a strange thing: there is no trace of the patch for the weaknesses that were noted in “[Finite-State Security Analysis of OTR Version 2][1]”.
It sounds very strange to me that authors of [OTRv2][2] and [OTRv3][3] did not manage to patch up the weak... |
In RSA, it is basically equivalent to use the private key $d$ to encrypt as it is to use the public key $e$ to encrypt. They are exactly inverses: $e=d^{-1}$.
I need to know, are there other public key schemes like this? Eg., I do not think Diffie-Hellman is like this.
Many thanks! |
I am trying to use AES as cipher for an application i am building.
I am using a JavaScript library (https://code.google.com/p/crypto-js/) to perform encryption and decryption with AES.
When i perform decryption, this happens:
AES.decrypt(msg, right_key) == 'message decrypted !' //true
AES.decrypt... |
Should AES.descrypt(msg, wrong_key) return blank or wrong result ? |
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