instruction stringlengths 15 30k |
|---|
I'd like to know if using the ECDH shared secret of a static EC Private Key with it's own corresponding static EC Public Key causes a problem / weakness.
###Background:
In this environment, several agents are producing and consuming data, and the streams are being protected with static ECDH keys.
The ECDH Shared... |
Can I use an ECDH Shared Secret from the same Private / Public Key Pair? |
I know how standard HMAC(key,msg) function works, and I want to write a Delphi port of HMAC class that implements Update function. The problem is that I don't understand how this Update function works (for example of Update function, see SSL definition here: https://www.openssl.org/docs/crypto/hmac.html).
If I under... |
No, it's not a problem.
What you've found is known as the *square computational diffie-hellman problem*(SCDH) and it can be shown that this is equivalent to the *computational diffie-hellman problem*(CDH).
For completeness:<br>
**SCDH**:<br>
Given $g$ (your $G$) and $g^x$ (your $Q$), find $g^{x^2}$ (your $d_A^2... |
I was tasked with making an expo about AES and its steps, but I still can't grasp it, especially when it comes to "key schedule".
Does anyone know some good material to start learning? Or can someone give me good explanations about AES? I tried Wikipedia and some random pdfs to no avail.
|
Where can I learn the basics of AES? |
I was tasked with making an expo about AES and its steps, but I still can't grasp it, especially when it comes to "key schedule".
Does anyone know some good material to start learning? Or can someone give me good explanations about AES? I tried Wikipedia and some random PDFs but nothing really fit the bill.
|
I understand that ECB does not hide data patterns well. But my understanding is that it cannot be broken to "know" the underlying message. If that was the case, why can't ECB be used with some obfuscation technique like say XORing with the address? I am talking about data stored in DDR - and assume it is not an image d... |
Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if Bob and Carol can send/receive messages to/from each other. This is what Alice wants to figure out
Bob and Carol are ... |
I'd like to know if using the ECDH shared secret of a static EC Private Key with it's own corresponding static EC Public Key causes a problem / weakness.
(edit) not asking if it's ok to re-use the keys multiple times. Static EC Keys are known to be ok in this usage case.
###Background:
In this environment, seve... |
Here is a relevant question: [enter link description here][1]
Using
openssl s_client -msg -connect google.com:443 -cipher ECDHE-RSA-AES128-SHA
I got something like:
<<< TLS 1.2 Handshake [length 014d], ServerKeyExchange
0c 00 01 49 03 00 17 41 04 1b cf 0c 41 e4 3a b7 ...
I've gone through th... |
Recently, Fujisaki and Okamoto provided a revised version of the Fujisaki-Okamoto transformation [1], a generic transformation for achieving IND-CCA2 security. This new version is slightly different than the original [2] and the security proof does not define a knowledge extractor (the original version actually proved ... |
I think we're all aware of the "classical" Weierstrass (short?) elliptic curve equation: $y^2\equiv x^3 + ax +b \pmod p$. Well known examples of these curves include the NIST's and Brainpool ones.
Now there's also the "Montgomery" representation: $by^2\equiv x^3 + ax^2 + x \pmod p$ where the famous Curve25519 is an ... |
Looking for the number of characters that can be encrypted using the The elliptic curve ElGamal cryptosystem of each block, I found these lines. But I cannot understand them:
> Actually in our case we need to divide into an even number of blocks. If we think in a
character as a number < 256 (its ASCII code) and we ... |
Looking for the number of characters that can be encrypted using the The elliptic curve ElGamal cryptosystem of each block, I found these lines. But I cannot understand them:
> Actually in our case we need to divide into an even number of blocks. If we think in a
character as a number < 256 (its ASCII code) and we ... |
I am trying to calculate an $x$, such that $t = g^x \pmod p$ in order to crack a weak ElGamal encryption for university.
I found GDlog, but I cant figure out how I can use the input to calculate my $x$.
Here is what we got (from gdlogs example code):
p:1000000000000000000000000000057 //prime number, modu... |
What does the acronym "CRT" stand for in the PKCS #1 specification? Does it stand for "Chinese Remainder Theorem"?
Thanks,
Pete |
What does the acronym "CRT" stand for in the PKCS #1 specification? |
I'm trying to get my server to establish trust with a client. Neither is on the Internet, so there are no certificate authorities. The typical way to establish trust in my domain is for a client to "request a seed", the server provides a seed, and the client "provides a key", and the server "verifies the key". (In c... |
I'm trying to get my server to establish trust with a client. Neither is on the Internet, so there are no certificate authorities. The typical way to establish trust in my domain is for a client to "request a seed", the server provides a seed, and the client "provides a key", and the server "verifies the key". (In c... |
We have the voting protocol that is described [here][1].
I am looking at the following exercise:
Determine how many dishonest tallying centres the protocol can cope with before the following properties no longer hold.
1. Only authorized voters will be able to vote.
2. No one will be able to vote more th... |
Voting protocol - How many dishonest tallying centres can the protocol cope with? |
I have been studying data compression for a while. For educational purposes, after a lot of reading, I managed to create a software that performs encryption and authentication using AES256-GCM. However, I have now reached a point after which I cannot find a possible answer and this is confusing me.
My software allow... |
How can complexity be increased or decreased in AES? |
This begs the question, why would you in *any* real-world circumstance wish to reduce the difficulty for an attacker to break your cryptosystem?
To answer your question practically, the only reasonable way I can think of to accomplish this is to simply reduce the entropy in the key. At 100%, all 128 bits of the key ... |
Edward curves were considered initially because it provides a unified formula for both doubling and addition, thus having inherent side-channel resistance. But a lot of work has been done recently involving construction of different class of addition an doubling formula(eg- differential addition formula, w-coordinate f... |
Why recently Edward curve formulas being developed that deviates from unification? |
###My understanding of Rabin
We have $p$ and $q$ which are distinct primes congruent to $3 \pmod 4$. Then we have $n = pq$.
Encryption is done as $e(m) = m^2 \pmod n$, where $m$ is our message.
Decryption is done by evaluating $d(c) = \sqrt{m} \pmod n$, where $c$ is our ciphertext. This can be accomplished ... |
###My understanding of Rabin
We have $p$ and $q$ which are distinct primes congruent to $3 \pmod 4$. Then we have $n = pq$.
Encryption is done as $e(m) = m^2 \pmod n$, where $m$ is our message.
Decryption is done by evaluating $d(c) = \sqrt{m} \pmod n$, where $c$ is our ciphertext. This can be accomplished ... |
I'm configuring a PKI infrastructure with an offline root CA and several issuing CAs. Among other topics, I'm struggling to decide how the revokation of an Issuing CA certificate works.
My Root CA will issue CRL once a year, and as far as I know, a machine with a CRL cached won't download a new CRL until the current... |
I want to send/receive messages with A (an peer) using TCP socket.<br>
I want to encrypt messages using AES CBC.<br>
Only I and A know a symmetric key K1 used in AES CBC, and K2 used in HMAC.<br>
The size of each message is small( < 100 bytes). <br>
Low latency is needed.<br>
(verification per message is needed.)<... |
Idea 1 is similar to what TLS actually does (and begs the question "why aren't you using TLS?"). Modern thought is that it'd be generally better if you first encrypt, and then perform the MAC, as in:
> E := AES(M)
> Send Encrypted, HMAC(Encrypted)
But no radical problem is known with your idea (unless you s... |
I am using a java jwt library [jose4j][1].
There is a list of digital signatures algorithms which can be used.
* HMAC using SHA-2
* RSASSA-PKCS1-V1_5 Digital Signatures with with SHA-2
* Elliptic Curve Digital Signatures (ECDSA) with SHA-2
* RSASSA-PSS Digital Signatures with SHA-2
I tried to understand... |
what are the advatanges and disatvantages of the digital signature algorithms for jwt? |
I am using a Java JWT library [jose4j][1].
There is a list of digital signatures algorithms which can be used.
* HMAC using SHA-2
* RSASSA-PKCS1-V1_5 Digital Signatures with with SHA-2
* Elliptic Curve Digital Signatures (ECDSA) with SHA-2
* RSASSA-PSS Digital Signatures with SHA-2
I tried to understand... |
what are the advatanges and disavantages of the digital signature algorithms for JWT? |
From my understanding both types of attack, collision and birthday are based on the principle of two randomly/pseudo-randomly chosen plain text to hash to the same value. I don't want to launch any biased supposition, but aren't they the same?
From the https://en.wikipedia.org/wiki/Collision_attack I found that _ev... |
What are the differences between collision attack and birthday attack? |
Idea 1 is similar to what TLS actually does (and begs the question "why aren't you using TLS?"). Modern thought is that it'd be generally better if you first encrypt, and then perform the MAC, as in:
> E := AES(M)
> Send IV, Encrypted HMAC(IV | Encrypted)
But no radical problem is known with your idea (unle... |
Here is the pseudocode for a routine I am designing:
encrypt(password, string):
nonce1 := generate_random_nonce()
nonce2 := generate_random_nonce()
key := derive_key(nonce1, password)
encrypted := cipher(nonce2, key, string)
return (nonce1 || nonce2 || encrypted || mac(key, enc... |
From my understanding both types of attack, collision and birthday are based on the principle of two randomly/pseudo-randomly chosen plain text to hash to the same value. I don't want to launch any biased supposition, but aren't they the same?
From [Collision attack wikipedia article](https://en.wikipedia.org/wiki/C... |
From my understanding both types of attack, collision and birthday, are based on the principle of two randomly/pseudo-randomly chosen plaintext to hash to the same value. I don't want to launch any biased supposition, but aren't they the same?
From [Collision attack wikipedia article](https://en.wikipedia.org/wiki/C... |
Here is a relevant question: [With OpenSSL and ECDHE, how to show the actual curve being used?][1]
Using
openssl s_client -msg -connect google.com:443 -cipher ECDHE-RSA-AES128-SHA
I got something like:
<<< TLS 1.2 Handshake [length 014d], ServerKeyExchange
0c 00 01 49 03 00 17 41 04 1b cf 0c 41... |
I understand that ECB does not hide data patterns well. But my understanding is that it cannot be broken to "know" the underlying message. If that was the case, why can't ECB be used with some obfuscation technique like say XORing with the address? I am talking about data stored in DRAM modules - and assume it is not a... |
Why can't I use ECB with some obfuscation for transient RAM? |
first af all sorry for my bad english.
I have to find a solution to this problem: i've a network composed by 1 server and some client. The server has a couple of key(public and private) and it share a secret key with each client. My goal is to exchange a session key between the server and the clients.
I've evalua... |
This begs the question, why would you in *any* real-world circumstance wish to reduce the difficulty for an attacker to break your cryptosystem?
To answer your question practically, the only reasonable way I can think of to accomplish this is to simply reduce the entropy in the key. At 100%, all 128 bits of the key ... |
I want to create a smart house project, and in that I bought some simple
RF modules. Those modules don't support crypto out of the box but I want to connect them to a device that I would program to use crypto (for example AES).
Now the question is since I would be sending a lot of same messages (digital I/O Pins... |
I thought a problem and want to ask if there's a more elegant solution.
**The scenario:**<br>
A company with a fileserver, which hosts encrypted documents.<br>
The files need to be accessible by about a dozen employees.<br>
Now the condition is, that each employee has different key material but all the employees ... |
Encrypt a file for multiple persons with different keys? |
Is it possible to use DES or 3DES over Galois Counter Mode (GCM) to provide authenticated encryption?
I haven't seen any implementation yet. |
There are quite a few block cipher modes of operation that require 128 bits. There are also modes of operation where a higher block size would even be practical. Is there a generic method of combining two blocks together in such a way that two 64 bit blocks can be seen as one 128 block? Is there an efficient method tha... |
There are quite a few block cipher modes of operation that require 128 bits. There are also modes of operation where a higher block size than 128, e.g. a block size of 256 bit would even be practical.
Is there a generic method of combining two blocks together in such a way that two 64 bit blocks can be seen as one 1... |
I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My goal is to exchange a session key between the server and the clients.
I've evaluated some solutions, but I am unsure i... |
I want to create a smart house project, and in that I bought some simple
RF modules. Those modules don't support crypto out of the box but I want to connect them to a device that I would program to use crypto (for example AES).
Now the question is since I would be sending a lot of same messages (digital I/O Pins... |
How can I use these properties to attack the DHKE? I know that the order of $a$ is always $2$ for $a = P - 1$ in $Z_p$. The subgroups generated by a will be $\{1,a\}$. |
I am struggling to understand how to calculate non-linearty of an s-box, could someone show me a detailed example? I found [“How to calculate non linearity of AES S-box?”][1] which helped a little, but I still don't really get it. If someone could show me an example I would appreciate it.
[1]: https://crypto.sta... |
How to calculate the non-linearity of an s-box? |
I recently skimmed over [two][1] [papers][2] on time-lock encryption and to get the data released on a specific point in time they'd extract some information from the blockchain, which can only be obtained if the blockchain has reached a certain size) and use this as a witness for witness encryption.
Now my question... |
What is "witness encryption"? |
In very short:
Assume you have an NP problem, stated as some condition to be met. Since it is a NP condition, the computational complexity to find a satisfying input (called the witness for the language) grows quite fast.
The setup of such an encryption scheme is based on a multilinear map (a generalization of a ... |
I want to implement a secure chat on mobile. I like to know if the following protocol for key agreement that use any asymmetric encryption exists:
Suppose Alice and Bob are two clients of the app. For this they have to register their public keys in a server, i.e,:
1. Alice generates her public and private keys (`... |
If we read the Google line information about how the cypher the https communication, it reads:
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
I understand it's using ECDHE to exchange keys, using ECDSA as digital signature and making the symmetric encryption with AES algorithm, using 128 bit keys. I don't know thoug... |
What's the GCM-SHA 256 of a TLS protocol? |
Imagine we have a scheme whose key length can be anything from $m$ to $n$ where $m<n$ and n $\leftarrow \{0,1\}^{10}$.
My question is: What is the size of key space for this scheme? |
I am trying to use the [Baby Step Giant Step](http://en.wikipedia.org/wiki/Baby-step_giant-step) algorithm to find discrete logarithm in:
$$a^x= B \pmod p$$
with using BSGS:
$$x = im+j$$
$$a^j = B a^{-im}$$ where
$m = \sqrt{p}$
Wikipedia says:
> A cyclic group of order $p$, having a generator $\alpha$ an... |
I have come up with the following rudimentary example of how ECC relates to asymmetric keys.
Is this a valid explanation of ECC and its relationship to asymmetry?
To only be deciphered by the person with the private key, it is necessary to use methods nontrivial in cryptography. To randomize the key, a set woul... |
We all know about public key cryptosystems, and we know some of these are computationally secure (for the time being, of course).
My question is, is there any algorithms out there which allow safe communication between peers in a non public/private key fashion?
If so, I would like to know some of these. If not, d... |
Is secure communication without public-key crytography feasible? |
We all know about public key cryptosystems, and we know some
<br>
of these are computationally secure (for the time being, of course).
My question is, are there any algorithms out there which allow safe
<br>
communication between peers in a non public/private key fashion?
If so, I would like to know some of t... |
We all know about public key cryptosystems, and we know some of these are computationally secure (for the time being, of course).
Are there any algorithms out there which allow safe communication between peers in a non public/private key fashion? If so, I would like to know some of these. If not, does any kind of fo... |
So studying double encryption (double DES) and understanding why it is subject to a Meet-in-the-middle attack, I tried to see if the same attack could be applied to a triple encryption with only two different keys and no decryption operation. I.e.:
c=E<sub>k2</sub>(E<sub>k1</sub>(E<sub>k1</sub>(m)))
,where c i... |
I'm bit confused about the subkeys that are used in Feistel ciphers. I know that all the subkeys k<sub>i</sub> are derived from the main key K, but how?
Say I have a simplified Feistel block cipher of i rounds, is it then correct to say that each key k<sub>i</sub> is the K/i part of the key?
So if the key is 4 by... |
How are subkeys, in Feistel block ciphers, derived for each round? |
Creating a 2048bits RSA keypair I figured that doing this using
- `openssl` takes as an input 32bytes of "randomness" from `/dev/urandom`
- `pgp` (openPGP) takes as input 300 bytes of "randomness" from `/dev/random`
My questions is. Does the number of randomness influence the cryptographic qualities of the r... |
Theoretically – is CBC mode harder to bruteforce when compared with ECB when assuming:
1. we ignore computational cost for the XOR operations, and
2. the IV is made public? |
> I know that all the subkeys $k_i$ are derived from the main key $K$, but how?
However the cipher designer feel like. The Feistel design gives guidance as to how the block is processed (and in a way to make inverting the cipher easy), however it gives no guidance as to actually generate the subkeys. The designers... |
We know block cipher algorithms. In the block cipher algorithms, Key Scheduling is the one crucial part. I see that in some simulation programs of the AES,DES,TripleDES encryption algorithms. In those, some programs are asking for the key dynamically or statically.
Now this time, I need to know clearly how to gener... |
I have downloaded and built [Cryptdb][1] and it works well. Most of queries on encrypted database run without any issue but, the query with `LIKE` key word receives an error.
mysql> select * from pptbl;
+------+-------+
| id | name |
+------+-------+
| 1 | ali |
| 2 | arbab |
... |
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 subs... |
What is Polymorphic encryption? |
Well i have downloaded some cryptographic algorithm. Do there are those I didn't understand so this is my question: What is polymorphic RC4 or Polymorphic xor encryption? |
Well i have downloaded some cryptographic algorithm. Do there are those I didn't understand so this is my question: What is polymorphic RC4 or Polymorphic xor encryption?
I heard this in malware encryption. |
Good blinding requires good randomness. Randomness is a hard requirement, especially for embedded systems. In a similar vein, the DSA and ECDSA signature algorithms require a strongly random integer (called _k_) for each signature, and several implementations have failed to use random enough values, with hilarious cons... |
We all know about public-key cryptosystems, and we know some of these are computationally secure (for the time being, of course).
Are there any algorithms out there which allow safe communication between peers in a non “public/private” key fashion? If so, I would like to know some of these. If not, does any kind of ... |
I am extremely new to cryptography, still trying to learn basics. I got stuck in the following example of an evesdropping experiment with private key.
$$\begin{array} {|r|r r r|r|}
\hline
C & & & & A \\
\hline
k & \leftarrow & Gen(1^{n}) & & \ \\
b & \leftarrow & {0, 1} & \leftarrow [m_0,m_1] \leftarrow & input... |
Perhaps you are referring to a polymorphic virus? This is a virus which consists of a decryption program along with the actual virus code which is encrypted. When the virus runs and subsequently spreads, it re-encrypts itself with a different key, thereby appearing to be different each time it propagates.
|
I'm facing to a project that is build a rainbow table to cracking DES.
I've already collected information about Hellman, DP, rainbow table method. Finally, I choose rainbow table. I've read topic [Rainbow table for DES with all-zero plaintext][1].
Now, my consideration how to choose good parameter to obtain highest ... |
I'm facing to a project that is build a rainbow table to cracking DES.
I've already collected information about Hellman, DP, rainbow table method. Finally, I choose rainbow table. I've read topic [Rainbow table for DES with all-zero plaintext][1].
Now, my consideration how to choose good parameter to obtain highest ... |
In MD5, there are four rounds. After every round, why do we need to add the computed $Q$ values to the initial values and then take this value as input to the next round. For example after the first round, we compute
$$Q^{\text{new}}_1=Q_{60}+Q_{-4}, \ Q^{\text{new}}_2=Q_{61}+Q_{-3}, \ Q^{\text{new}}_3=Q_{62}+Q_{-2}... |
I'm facing a project where I need to build a rainbow table to break DES.
I've already collected information about Hellman, DP, rainbow table method. Finally, I chose the rainbow table approach. I've read about the topic [“Rainbow table for DES with all-zero plaintext”][1].
Now, my consideration how to choose good pa... |
the worst-case one way function is defined as follows
$$\forall A \exists x : pr(A(f(x))\in f^{-1}(f(x)))\neq 1$$
can you give any example of such function? |
I understand how to implement a Meet-in-the-Middle attack on 2DES/3DES, by computing for one half all possible keys and storing the outcome and then subsequently do the same for the other half but compare with the previously stored outcome to see if there is a match somewhere. Very unprecise description I know but just... |
I understand how to implement a Meet-in-the-Middle attack on 2DES/3DES, by computing for one half all possible keys and storing the outcome and then subsequently do the same for the other half but compare with the previously stored outcome to see if there is a match somewhere. Very unprecise description I know but just... |
I am extremely new to cryptography, still trying to learn basics. I got stuck in the following example of an eavesdropping experiment with a private key.
$$\begin{array} {|r|r r r|r|}
\hline
C & & & & A \\
\hline
k & \leftarrow & Gen(1^{n}) & & \ \\
b & \leftarrow & {0, 1} & \leftarrow [m_0,m_1] \leftarrow & in... |
Daniel J. Bernstein's [ChaCha][1] core is an evolution of the [Salsa20][2] core. Both are functions over the set of 512-bit bitstrings, partitioned as sixteen 32-bit words.
Can we exhibit collisions, or second-preimages (with implies the former), for the ChaCha core?
The Salsa20 core has the easily verified prope... |
Collision or second preimage for the Chacha core? |
http://crypto.stackexchange.com/questions/10526/how-broken-is-a-xor-of-two-lcgs
http://crypto.stackexchange.com/questions/20495/how-brittle-are-lcg-cracking-techniques
Based on the above two questions, I have simply one additional question: how broken is a XOR of two 64-bit multiply with carry generators, with one ... |
How broken is a xor of two multiply with carry generators? |
Daniel J. Bernstein's [ChaCha][1] core is an evolution of the [Salsa20][2] core. Both are functions over the set of 512-bit bitstrings, partitioned as sixteen 32-bit words.
Can we exhibit collisions, or second-preimages (with implies the former), for the ChaCha core?
The Salsa20 core has the easily verified prope... |
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