instruction stringlengths 15 30k |
|---|
I'll take the [(previous version of the) question][1] as: how to implement a secure hash function $H3$ with 3 arguments, from one hash function $H$ with 1 argument, all with argument(s) in $\{0,1\}^*$.
Note: For a concrete $H$ with the destination set $\mathbb Z_p^*$ thought in the question, we could use [SHA3-512][... |
I'll take the [(previous version of the) question][1] as: how to implement a secure hash function $H3$ with 3 arguments, from one hash function $H$ with 1 argument, all with argument(s) in $\{0,1\}^*$.
Note: For a concrete $H$ with the destination set $\mathbb Z_p^*$ thought in the question, we could use [SHA3-512][... |
Alice and Bob meet regularly. They have agreed face-to-face a 128 bit password which they want use to encrypt/decrypt emails written between them.
They decide to use 256-bit AES. Alice wrote her message, but found that every AES 256 application she used to encrypt her text provided a different ciphertext. She could ... |
Why don’t all AES encryption tools used to encrypt an identical message with the same password produce the same ciphertext? |
Alice and Bob meet regularly. They have agreed face-to-face a 128 bit password which they want use to encrypt/decrypt emails written between them.
They decide to use 256-bit AES. Alice wrote her message, but found that every AES 256 application she used to encrypt her text provided a different ciphertext. She could ... |
It depends on the time you want to spend. But most likely, there is nothing with reasonable efficiency. For arithmetic operations, humans are really bad compared to computers, and the difference is at least a factor of $10.000.000$ (very very rough guess, probably even 1+ additional zeros there).
So, since you have ... |
Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group Z_p? |
Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group $\mathbb Z_p$? |
In the event this is a homework question, I'll give an answer that would be improbably correct so you may not use it. ;) But maybe people won't accuse you of asking a homework question if you would source where you got the example?
The password and the key are two different things. Early cryptographic implementation... |
I'm quite new to the topic and read a bit about poodle and padding oracle.
I quite understand the "regular" padding oracle attack, substituting the last byte of block(n-1) to determine the last byte of block(n) - by "myguess" XOR 0x01 for the last byte and so on.
Articles on poodle however state, that the attack ... |
poodle padding multiple blocks? |
I am studying about different operation modes of block ciphers my question isn't something specific to that, but is how these operation modes are used in cryptography?
I have this picture here (OFB-mode):
![enter image description here][1]
([source][2])
I would like to know how these operations are combined w... |
Operation modes of block ciphers how are used? |
Why don’t all AES encryption tools produce the same key from the same password? |
How to decrypt a PGP message with only the two primes and the public exponent? |
What is the difference between **H(M)** and **H3(M, s, IDA)**?
I am aware of Hash function with a Message and a Key, but there are three parameters in:
**H3(M, s, IDA)**.
Here **M** is the message, **s** is the key, and **IDA** is the identity of user A.
I meant that how to implement secure hash **H3(M,s,IDA... |
We are creating a device with a small microcontroller (20 MHz CPU 16 KiB RAM).
We need some way to securely send signed files to device (only signature, no encryption necessary). An external company has come up with an elliptic curve solution but it needs about a minute to verify a signature, without counting the fi... |
There are [modular-root signature systems](http://cr.yp.to/sigs/rwsota-20080131.pdf) other than standard RSA.
Can the device [interact with a party that is allegedly the signer] during verification?
<br>
If no, can it interact with a more powerful computer that does not need to be the signer?
<br>[hardware](http:... |
I have read the paper "Differential Power Analysis of HMAC SHA-2
in the Hamming Weight Model" (http://www.di.ens.fr/~belaid/articleHMAC.pdf) and I want to understand the DPA Attack. In section 3.2.1 Path 1 (page 4) there is written:
" The last remaining parts H$^{(0)}$ and C$^{(0)}$ can be recovered by making subst... |
The specification for OMAC has the following to say about OMAC2:
<blockquote>
For OMAC2, we adopted u<sup>−1</sup> instead of u<sup>2</sup> as Cst<sub>2</sub>. It requires one right shift to compute L· u<sup>−1</sup> instead of one left shift to compute (L· u)· u. This would allow to compute both L · u and L · u<su... |
Why does OMAC2 exist? |
I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers mod n).
In some crypto papers and documents I've read that 'g' needs to be a primitive root mod n ('g' order in G = phi(p)), but we actually use g as a generator of a large subgroup of q order, where q is a large prime extracte... |
I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers mod n).
In some crypto papers and documents I've read that 'g' needs to be a primitive root mod n ('g' order in G = phi(p)), but we actually use g as a generator of a large subgroup of q order, where q is a large prime extracte... |
The algorithm for mental poker that I saw on Wikipedia and everywhere else relies on an encryption algorithm such that $E_k(E_j(P)) = E_j(E_k(P))$, but I can't find a modern and secure algorithm for which this is true. The only algorithm I found with this property is SRA (I believe that's what it's called) but it relie... |
Is there a mental poker algorithm that does not rely on commutative encryption? |
It seems that several file encryption systems do NOT use authenticated encryption. (E.g. gpg --symmetric and boxcryptor as far as I can determine). I understand that this is generally considered [insecure][1], but is not demanded of full disk encryption. But for individual file encryption, for example where one is sto... |
What is the right notion of security to use for file encryption? |
I am studying about the AES encryption standard, and as I know from the theory there is no known weaknesses today about this block-cipher.
I would like to find out or at least to understand what "classification" of secureness is AES.
As I know there are several classifications:
1. Perfectly secure. Which is n... |
Can AES be considered as Perfectly Secure? |
I think you meant brute force when you mention, it would take trillions(?) years to break AES. So your "provably secure" category boils downs to brute forcing the algorithm which is not considered "breaking" the algorithm.
AES is kind of a successor to DES (at least for an initial understanding) which had been in us... |
I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers mod n).
In some crypto papers and documents I've read that 'g' needs to be a primitive root mod n ('g' order in G = phi(p)), but we actually use g as a generator of a large subgroup of q order, where q is a large prime extracte... |
I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers mod n).
In some crypto papers and documents I've read that 'g' needs to be a primitive root mod n ('g' order in G = phi(p)), but we actually use g as a generator of a large subgroup of q order, where q is a large prime extracte... |
Given that the bottleneck on the embedded device is public-key signature verification, the best industry standard is RSA (with a standard signature padding, such as [PKCS#1 RSASSA-PSS][1], [PKCS#1 RSASSA-PKCS1-v1_5][2]), which is significantly faster than ECDSA for signature verification, including for the common $e=65... |
Given that the bottleneck on the embedded device is public-key signature verification, the best industry standard is RSA (with a standard signature padding, such as [PKCS#1 RSASSA-PSS][1], [PKCS#1 RSASSA-PKCS1-v1_5][2]), which is significantly faster than ECDSA for signature verification, including for the common $e=65... |
Given that the bottleneck on the embedded device is local (non-interactive) public-key signature verification, the best industry standard is RSA (with a standard signature padding, such as [PKCS#1 RSASSA-PSS][1], [PKCS#1 RSASSA-PKCS1-v1_5][2]), which is significantly faster than ECDSA for signature verification, includ... |
In format preserving encryption an attacker knows the format and data type of the plain text. The format of the plain text and cipher text are same. usually cipher text are unreadable form. then how FPE is secure?what are all the possible attacks on FPE cipher? |
I have read the paper "Differential Power Analysis of HMAC SHA-2
in the Hamming Weight Model" (http://www.di.ens.fr/~belaid/articleHMAC.pdf) and I want to understand the DPA Attack. In section 3.2.1 Path 1 (page 4) there is written:
" The last remaining parts H$^{(0)}$ and C$^{(0)}$ can be recovered by making subst... |
Given that the bottleneck on the embedded device is local (non-interactive) public-key signature verification, the best industry standard is RSA (with a standard signature padding, such as [PKCS#1 RSASSA-PSS][1], [PKCS#1 RSASSA-PKCS1-v1_5][2]), which is significantly faster than ECDSA for signature verification, includ... |
Given that the bottleneck on the embedded device is local non-interactive public-key signature verification, the best industry standard for that is RSA (with a standard signature padding, such as [PKCS#1 RSASSA-PSS][1], [PKCS#1 RSASSA-PKCS1-v1_5][2]), which is usually significantly faster than ECDSA for signature verif... |
I want to use a key derivation function to derive a key to another one.
I think HKDF is the easiest solution in my case.
The following picture gives a clear definition of it :
http://webee.technion.ac.il/~hugo/kdf/hkdf-fig.jpg
In the case where the number of key bits request from the KDF is equal to the hash ... |
We are attempting to integrate our application in to a third party system. To do this we need to pass encrypted passwords in to this system. I have decompiled the assembly and looking at the code it seems that they are using something similar to XOR encryption (In a production system...) From what I can see from the de... |
Can you identify this algorithm? |
1. Look up the OpenPGP secret key format (some kind of ASN.1 I think?).
2. Use your favourite bignum implementation to multiply p by q and store this as the modulus n (in the correct format).
3. To calculate the decryption exponent, you need $d$ such that $ed=1 \pmod{(p-1)(q-1)}$. This can be found with the extend... |
We are attempting to integrate our application in to a third party system. To do this we need to pass encrypted passwords in to this system. I have decompiled the assembly and looking at the code it seems that they are using something similar to XOR encryption (In a production system...) From what I can see from the de... |
I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'm posting it here:
1. Alice and Bob have a pair of numbers, the generator g and the modulus P, these numbers are si... |
My attempt of solving socialist millionaire. Is it good? |
Is it possible to construct a set membership proof to show $\delta \in \Psi$ where $\delta$ is publicly known and $\Psi$ should stay only known to the prover?
It seems rather impossible but I would like some confirmation. |
I am reading the page 39 in this ["Post Quantum Cryptography"](http://www.e-reading-lib.org/bookreader.php/135832/Post_Quantum_Cryptography.pdf") book. Why does equation 15 hold? There is no further knowledge about f and you definitely cannot use any power laws. So, why is $f^{2^w-1-b_i}(f^{b_i}(x_i)) = f^{2^w-1} $ val... |
I am reading page 39 in this ["Post Quantum Cryptography"](http://www.e-reading-lib.org/bookreader.php/135832/Post_Quantum_Cryptography.pdf") book. Why does equation 15 hold? There is no further knowledge about f and you definitely cannot use any power laws. So, why is $f^{2^w-1-b_i}(f^{b_i}(x_i)) = f^{2^w-1} $ valid?
... |
I have this curve in E(F131) : $$Y^2 = X^3 + X + 2 $$
I want calculate the sum P + Q considering that $$P= (5,1)$$ and $$ Q = (60, 49)$$
For calculate the result i use these formulas:
$$ xr = ((y2 - y1) / (x2-x1)) ^2 - x1 - x2$$
$$ yr= -y1 + ((y2 - y1) / (x2 - x1)) * (x1 - xr)$$
I need to obtain as re... |
I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers $\mod n$).
In some crypto papers and documents I've read that 'g' needs to be a primitive root mod n ('g' order in G = phi(p)), but we actually use g as a generator of a large subgroup of q order, where q is a large prime extra... |
I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers $\mod n$).
In some crypto papers and documents I've read that $g$ needs to be a primitive root mod $n$ ($g$ order in $G = \phi(p)$), but we actually use $g$ as a generator of a large subgroup of order $q$, where $q$ is a large ... |
**Reductionist security**
In a reductionist security proof for some cryptographic protocol $\Pi$
to some alleged hard problem $P$ means, that we can build an algorithm
$\cal B$ for solving $P$ if we have access to a hypothetical algorithm
$\cal A$ that efficiently breaks the security definition for the
protocol ... |
I intend to authenticate small packets of data, between 16 and 256 bytes each. For some of them encryption will also be required. This will be used on small micro controllers, with RAM sizes ranging in 1 KB to a 64 KB.
My initial approach was to use AES-128 as the base cipher for a block cipher mode with MAC (GCM fo... |
> how do we obtain the original message if we XOR the ciphertext with some other key stream, different from the one that we used to encrypt the message in Secure Channel: Sending a Message?
Answer: we don't use different keystreams. When Alice sends Bob a message, she uses the 'Enc Alice to Bob' keystream, When Bo... |
Having an ElGamal encryption scheme with p=19 which value can not be assigned to
g?
The answers were : 1,7,11,2
I think you can't assign value 1 to g. |
I would like to better understand the operation of the LED algorithm, especially the process of substitution and permutation of the blocks and especially the use of the keys in each round.
The keys in each round are expansions of a single key or keys are different?
Already consulted sources:
https://www.crypto... |
I've done some research into this, but I'm still not sure why this cannot be implemented. Provided we share an initial OTP, possibly via USB or some other physically secure method, surely we can include the next one in the messages that follow.
More specifically, if I were to take a pad of double length, splitting i... |
Why is it impossible to implement an “infinite” one time pad algorithm over a computer network? |
Having shared a pad of length double the length of your anticipated message, splitting it into x and y.
Then using x to encrypt the message, and using y twice to encrypt the next pad, would that be insecure (seeing as the data I'm encrypting would still be random)? |
Is this adaptation of one-time-pad still secure? |
My name is Sofu Rizky, I am from Indonesia.
I am researching about Lightweight Hash Function, I want to ask you about Lightweight Hash Function.
1. Why The PHOTON can be said Lightweight?
2. What The standard or requirement a hash function algorithm can be said to be lightweight ?
Thank you. |
I am researching about lightweight hash functions and I've got two related questions:
1. What is the standard or requirement for a hash function in general to be considered lightweight ?
2. Why can it be said that the PHOTON hash function is lightweight?
|
Your questions are 1) is there any research in this area? and 2) is this worth researching? which are still mostly unanswered. Even though there is an accepted answer, i'll take a shot at answering your questions.
1) Yes, there is a lot of research in this area. Here are the talks I'd recommend:
- Blackhat 2010... |
Is there any way to parallelize AES running in CBC mode? (The plan is to parallelize it using OpenMP) |
Can AES in CBC mode be parallelized? |
Why using AES in CBC mode a bad idea? is CTR mode better? Given only these two can be used for parallelization. |
Why using AES in CBC mode a bad idea? |
Why using AES in EBC mode a bad idea? is CTR mode better? Given only these two can be used for parallelization. |
Why using AES in ECB (Electronic Code Book) mode a bad idea? is CTR mode better? Given only these two can be used for parallelization. |
I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'm posting it here. Here's how it would work together with Diffie Hellman to prevent man in the middle attacks:
1. A... |
Why using AES in ECB (Electronic Code Book) mode a bad idea? |
GM is a cryptosystem with a modulus $N = pq$ ($p$, $q$ prime) and quadratic nonresidue $r \in (\Bbb Z / N\Bbb Z)^*$ as the public key. You can see the details on Wikipedia.
Anyway, let's say that $N < 2^{1024}-1$. Then the ciphertext can be represented as a $1024$-bit string regardless of $N$. In which case, you can... |
GM is a cryptosystem with a modulus $N = pq$ ($p$, $q$ prime) and quadratic nonresidue $r \in (\Bbb Z / N\Bbb Z)^*$ as the public key. You can see the details on Wikipedia.
Anyway, let's say that $N < 2^{1024}$. Then the ciphertext can be represented as a $1024$-bit string regardless of $N$. In which case, you can t... |
GM is a cryptosystem with a modulus $N = pq$ ($p$, $q$ prime) and quadratic nonresidue $r \in (\Bbb Z / N\Bbb Z)^*$ as the public key. You can see the details on Wikipedia.
Anyway, let's say that $N < 2^{1024}$. Then the ciphertext can be represented as a $1024$-bit string regardless of $N$. In which case, you can t... |
I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'm posting it here. Here's how it would work together with Diffie Hellman to prevent man in the middle attacks:
1. Al... |
I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'm posting it here. Here's how it would work together with Diffie Hellman to prevent man in the middle attacks:
1. Al... |
2 3 1 1
1 2 3 1
1 1 2 3
3 1 1 2
In the above MDS matrix, used in AES encryption, why the number 2,3 and 1 is chosen/calculated, why not any other number ? |
My attempt of combining socialist millionaire and Diffie-Hellman. Is it any good? |
$$\begin{pmatrix}2&3&1&1\\
1&2&3&1\\
1&1&2&3\\
3&1&1&2\end{pmatrix}$$
In the above MDS matrix used in AES encryption, why are the numbers $2$,$3$ and $1$ chosen? Why not any other number? |
How was the MDS matrix used in AES chosen? |
Daniel J. Bernstein (and others) [have expressed concern](http://safecurves.cr.yp.to/bada55.html) over how "verifiably random" curve parameters are generated. He points out that hashing a public seed doesn't prevent, say, the US government (NIST/NSA) from choosing a seed that produces parameters with a one-in-a-millio... |
Would key stretching help mitigate concerns with "verifiably random"? |
No, not really. The problem is that these kind of parameters may themselves be chosen deliberately. In other words, NIST/NSA may have performed pre-calculation that still puts a value that opens the algorithm up to some kind of attack.
Lets take an example, would you trust: `SHA-256^40("Trust me, I'm an innocent str... |
I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'm posting it here. Here's how it would work together with Diffie Hellman to prevent man in the middle attacks:
1. Al... |
The biggest problem with using MtE with a mode where it's known to be secure (CBC) is with the padding, where you can't retrieve the authentication until you know where it is by looking at the padding bytes.
Instead, why not just place the MAC at the very end of the last block, and include the padding bytes in the c... |
Why not put MAC in fixed position and cover padding for MAC-then-encrypt? |
How can you both
"include the padding bytes in the calculation of the MAC? Verify the MAC before even looking at the padding"
It sounds like your construction is trying to be
Encryption:
m0 || m1 || m2 || padding || padding of padding || MAC of m0+m1+m2+first padding --CBC--> ciphertext
Decryptio... |
The biggest problem with using MtE with a mode where it's known to be secure (CBC) is with the padding, where you can't retrieve the authentication until you know where it is by looking at the padding bytes.
Instead, why not just place the MAC at the very end of the last block, and include the padding bytes in the c... |
Test vectors for PRESENT algorithm? |
I want to split a message using sss by splitting each byte of it so the field i'm using is 2^8.
Assume (2,2) scheme, i.e., splitting it into 2 shares and both of them are needed for reconstruction.
By having one share, i can guess the second (i have max 256 options) and try to build the polynomial to reveal the secre... |
Yesterday I finished programming my own encryption program. It is using an input and a key. Here are all the steps it is going through. For an example, let say the `input is "Hello"` and the `key is "Hi"`
1. You take the input and convert it into binary:
`01001000 01100101 01101100 01101100 01101111`
2. You ... |
Made my own encryption-program, can someone tell me how safe it is? |
Yesterday I finished programming my own encryption program. It is using an input and a key. Here are all the steps it is going through. For an example, let say the `input is "Hello"` and the `key is "Hi"`
1. You take the input and convert it into binary:
`01001000 01100101 01101100 01101100 01101111`
2. You ... |
I want to split a message using sss by splitting each byte of it so the field i'm using is $2^8$.
Assume $(2,2)$ scheme, i.e., splitting it into $2$ shares and both of them are needed for reconstruction.
By having one share, i can guess the second (i have max $256$ options) and try to build the polynomial to reveal t... |
I want to split a message using Shamir's Secret Sharing by splitting each byte of it so the field I'm using is $2^8$.
Assume $(2,2)$ scheme, i.e., splitting it into $2$ shares and both of them are needed for reconstruction.
By having one share, can I guess the second (I have max $256$ options) and try to build the po... |
The definition of an unconditionally secure cryptosystem states that the cryptosystem cannot be broken even with infinitely computational ressources and time.
However, since most books define the keyspace $\mathcal K$ to be finite, then with infinite time any computational device can perform an **exhaustive keysearch*... |
How can a cryptosystem be unconditionally secure? |
No, not really. The problem is that these kind of parameters may themselves be chosen deliberately. In other words, NIST/NSA may have performed a pre-calculation to make sure that the key stretching outputs a value that opens the algorithm up to some kind of attack.
Lets take an example, would you trust: `SHA-256^40... |
I have noticed, during the period I spent studying RSA, that Euler's Totient function can be calculated in another way than $ϕ(N) =(p-1).(q-1)$
Let me explain myself by pointing to a brief example:
$p = 131$
$q = 11953$
$N= p*q = 1565843$
The totient defines the quantity of positive integers less or equa... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.