instruction stringlengths 15 30k |
|---|
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
A video camera *can* obtain entropy, but only at a fairly low rate and only if allowed to see "unusual" scenes… like someone making funny faces, unusual movements, etc. Of course, this only works in a room with no video bugs.
**Theoretical explanations…**
Depending on your knowledge-range, the following sources ... |
I'm having a rough time understanding the math behind elliptic curves.<br>
I want to implement **ECDH** where user can define **a, b,** and **p** parameters of elliptic curve.
How can I calculate generator base point **G**? Is it any point that satisfies elliptic curve equation $ y^2 \equiv x^3 + ax + b \pmod p$?
... |
as you know occur some successful attacks again mifare classic tags(manufactured by NXP ) & therefor NXP recommendations to altering these tags with some newer products like mifare pro desfire &...
my question is why we don't encrypt data (with AES & ...)& then translate & store these data to the mifare classic's bloc... |
As you know there occured some successful attacks again mifare classic tags (manufactured by NXP) and therefore NXP recommends to replace these tags with some newer products like mifare pro desfire and others.
My question is why don't we encrypt data (with AES, ...) and then translate and store this data to the mifa... |
Say I want to encrypt something using RSA / KEM and an authenticated cipher. I encrypt using the following scheme:
1. generate random seed `z` using `n - 1` bits - where `n` is the size of the modulus `N`
2. interpret the seed `z` as unsigned number and encrypt using the public key `e`: `w = RSA(e, z)`
3. deriv... |
This may sound weird:
What if I don't let others know my public key, then use my private key to encrypt, and the public key to decrypt? Is this secure?
Let me explain a little bit:
----------
**Common usuage**: use private key to sign and disclose public key, then others can vefriy the data signature use pu... |
You can safely use ECB if all of the following conditions are met:
* Your messages can be unambiguously encoded in a form with a fixed size which is equal to the cipher's block size. For example, your messages all have the same size which is smaller than the block size, or they're all smaller than the block size and... |
I've written a C# Library that I hope will be used for security purposes in a commercial application. The application will communicate through the internet and not on an internal network. I am using RSA for Asymmetric Encryption and Rijndael for Symmetric Encryption. Currently the process I am using is as follows:
... |
Is it safe to reuse a symmetric key when using asymmetric encryption? |
Why not use the mature, analysed, and successful pattern of PGP communications?
First each party exchange the public keys of both the Client and Server.
Even better out of band verify them depending on your threat model (i.e. phone call or some other independent method of verification of each side's identity) whi... |
Why not use the mature, analysed, and successful pattern of PGP communications?
First each party exchange the public keys of both the Client and Server.
Even better out of band verify them depending on your threat model (i.e. phone call or some other independent method of verification of each side's identity and ... |
Why not use the mature, analysed, and successful pattern of PGP communications?
First each party exchange the public keys of both the Client and Server.
Even better out of band verify them depending on your threat model (i.e. phone call or some other independent method of verification of each side's identity and ... |
Why not use the mature, analysed, and successful pattern of PGP communications?
First each party exchange the public keys of both the Client and Server.
Even better out of band verify them depending on your threat model (i.e. phone call or some other independent method of verification of each side's identity and ... |
Why not use the mature, analysed, and successful pattern of PGP communications?
First each party exchange the public keys of both the Client and Server.
Even better out of band verify them depending on your threat model (i.e. phone call or some other independent method of verification of each side's identity and ... |
Enciphering data using AES and moving that to a card without effective security is not enough to solve some very real security issues; including most preeminently the possibility of
- returning a prepaid card to its original state, re-crediting it after use (an adversary can copy the original enciphered data, and sa... |
I have high performance nodes communicating with each other sending logs and data over network.
The communication is heavy and over public network.
I would like to know how to know which is the best encryption algorithm to be used to encrypt and decrypt the data so that it has minimal affect over performance simalt... |
Which data encryption mechanism to use for data transfer? |
I have high performance nodes communicating with each other sending logs and data over network.
The communication is heavy and over public network.
I would like to know how to know which is the best encryption algorithm to be used to encrypt and decrypt the data so that it has minimal affect over performance simult... |
I can find [descriptions][1] of using CFB mode to create a MAC and even [implementations][2], but cannot find any standard or papers analyzing its security bounds.
Is there a standard for CFB-MAC?
Where can I find an analysis of its security bounds?
[1]: http://crypto.stackexchange.com/questions/21167/why-... |
Enciphering data using AES and moving that to a card without effective security is not enough to solve some very real security issues; including most preeminently the possibility of
- returning a prepaid card to its original state, re-crediting it after use (an adversary can copy the original enciphered data, and sa... |
>...the standard javax.crypto package does not offer a PBKDF2WithHmacSHA512 implementation, how is that so?
[Starting with Java8](https://docs.oracle.com/javase/8/docs/technotes/guides/security/StandardNames.html), there is support for *PBKDF2With<prf>* where <prf> can be any number pseudo-random functio... |
Enciphering data using AES and moving that to a card without effective security is not enough to solve some very real security issues; including most preeminently the possibility of
1. returning a prepaid card to its original state, re-crediting it after use (an adversary can copy the original enciphered data, and s... |
I have a client which does the following:
salt = randomBytes(15)
iv = randomBytes(16)
// secret is a user-specified passphrase
key = pbkdf2(secret, salt)
message[0] = [salt, iv]
message[1..n] = encrypt('message content', key, iv)
// to notify server that message stream is ende... |
Is it safe to exchange cryptographic salt and initialization vector in messages? |
By definition of the notation $a\equiv b\pmod c$, this means $a-b$ is a multiple of $c>0$. Therefore, $17\cdot-7\equiv1\pmod{\varphi(N)}$ means that $(17\cdot-7)-1$ is a multiple of $\varphi(N)$.
Thus the answer to: "_how come_ $17\cdot-7\equiv1\pmod{\varphi(N)}$" is just: because $(17\cdot-7)-1$ is $-120$, which is... |
I went to a payment page on a site recently, and chrome was warning me that the page is possibly not secure, I have a very basic understanding of crypto but not enough to fully understand why this page is possibly not secure.
The cert comes from Thawte, which from what I found on google is a well trusted CA, howeve... |
Is the warning given by chrome warranted ? |
I have a client which does the following:
salt = randomBytes(16)
iv = randomBytes(16)
// secret is a user-specified passphrase
key = pbkdf2(secret, salt)
message[0] = salt.toHex() + iv.toHex()
message[1..n] = encrypt('message content', key, iv)
// to notify server that message... |
I have a client which does the following:
salt = randomBytes(16)
iv = randomBytes(16)
// secret is a user-specified passphrase
key = pbkdf2(secret, salt)
message[0] = salt.toHex() + iv.toHex()
message[1..n] = encrypt('message content', key, iv)
// to notify server that message... |
Client and server have given generator 3 and modulus which is 256 bit prime same all the time for all clients and server (simply hardcoded).
They both generate a private exponent and send result to each other and generate secure key. This all is done over insecure channel. That's all simple Diffie-Hellman exchange.
... |
Is simple XOR with secret key using DHE secure? |
> After this step every sent packet is encrypted over simple XOR block cipher by secure key's bytes, in this case 256bit long block.
Does this mean "divide the message into 256-bit blocks, and XOR each block with the key"? If so, this is very insecure. If any part of the message is predictable, the attacker can re... |
Suppose we have some Fibonacci LFSR, and it outputs some sequence.
How to change starting LFSR so, that it outputs exactly same sequence, but in reverse order? |
I went to a payment page on a site recently, and chrome was warning me that the page is possibly not secure, I have a very basic understanding of crypto but not enough to fully understand why this page is possibly not secure.
The cert comes from Thawte, which from what I found on google is a well trusted CA, howeve... |
Is the warning given by chrome warranted? |
I have a follow-up question about the extended Euclidean algorithm, as applied to RSA key generation, described in [this answer](http://crypto.stackexchange.com/questions/5889/calculating-rsa-private-exponent-when-given-public-exponent-and-the-modulus-fact/5894#5894).
Let us say we have $p=5$, $q=11$ and $e=17$, so ... |
Why can we ignore $y$ when using the extended Euclidean algorithm to calculate an RSA decryption exponent? |
Let's say I have generated a private and a public key. I create a message and encrypt it with the public key. I deliver this encrypted message and a private key to multiple recipients.
Why would I do this?
I want to be able to deliver a message that can only be decrypted. I don't want anyone to be able to encrypt... |
> the cert's signature algorithm and hash algorithm are `sha1RSA` and `sha1` respectively. I was under the impression that these were obsolete and have been for quite some time?
Yup, and that is indeed the problem. You're right that HMAC-SHA1 is still safe. RSA signatures, however, do not use HMAC: they just use a... |
> Also, if I give people the private key, and I keep the public key safe, am I right in believing that it's possible to generate a new public key just using the private key itself?
Correct. The private key contains the modulus, one or more of the primes, the private exponent and often some other relevant things. The... |
There are *four* issues (basically all you *can* get at once I think) going on with your connection to this site which is why Chrome warns you.
The first one is quite easy to spot: The usage of SHA-1 for the certificate signature. SHA-1 is generally considered deprecated and should not be used for scenarios where co... |
As you know there occured some successful attacks again mifare classic tags (manufactured by NXP) and therefore NXP recommends to replace these tags with some newer products like mifare pro desfire and others.
My question is why don't we encrypt data (with AES, ...) and then translate and store this data to the mifa... |
There are *four* issues (basically all you *can* get at once I think) going on with your connection to this site which is why Chrome warns you.
The first one is quite easy to spot: The usage of SHA-1 for the certificate signature. [SHA-1 is generally considered deprecated and should not be used for scenarios where c... |
I'm trying to design a serial key system, but it's too easy to crack as it is. To alleviate this, I'm trying to encrypt the serial key, but I have not yet found an encryption method that does what I want:
* Take *n* characters in, and spit out *n* characters.
* Symmetrical and requires a key
* Only outputs alphanu... |
Is there an encryption format that preserves length and only outputs alphanumerics? |
I'm trying to design a serial key system, but it's too easy to crack as it is. To alleviate this, I'm trying to encrypt the serial key, but I have not yet found an encryption method that does what I want:
* Take *n* characters in, and spit out *n* characters.
* Symmetrical and requires a key
* Only outputs alphanu... |
I'm trying to design a serial key system, but it's too easy to crack as it is. To alleviate this, I'm trying to encrypt the serial key, but I have not yet found an encryption method that does what I want:
* Take 20 characters in, and spit out 20 characters.
* Symmetrical and requires a key
* Only outputs alphanume... |
I'm trying to design a promo code system for a server app I'm designing. Basically, I generate a promo code for a certain item and give the code out to someone, who then types it into the server.
Currently, the generator I wrote gives out a 20-character alphanumeric code, but the codes are too easy to manipulate. To... |
Can we implement AES with **16 bit block size** ?if so what are its advantages and disadvantages?Is there **any rule AES** has to be implemented with 128,192,256 ?Can we use AES for **odd number of bits**(17,33,37..) ? |
Implement AES with 16 bit block size? |
I am wondering about the crypto-period for keys used in pseudo-random functions.
For example, let's say I am using HMAC-SHA256 with a secret key $K$.
After how many computes do I have to update $K$? |
Has there ever been more then a theoretical difference between preimage resistance and second preimage resistance? |
I have an application that needs a fast 128-bit MAC to guarantee message authenticity in a protocol. I would like to reuse this MAC value as a binding identifier, so that even those who know the key cannot later generate another message with the same MAC value for that key.
"Second preimage resistance", or whatever ... |
Fast 128-bit MAC with second preimage resistance? |
By definition of the notation $a\equiv b\pmod c$, this means $a-b$ is a multiple of $c>0$. Therefore, $17\cdot-7\equiv1\pmod{\varphi(N)}$ means that $(17\cdot-7)-1$ is a multiple of $\varphi(N)$.
Thus the answer to: "_how come_ $17\cdot-7\equiv1\pmod{\varphi(N)}$" is just: because $(17\cdot-7)-1$ is $-120$, which is... |
I have high performance nodes communicating with each other sending logs and data over network.
The communication is heavy and over public network.
I would like to know how to know which is the best encryption algorithm to be used to encrypt and decrypt the data so that it has minimal affect over performance simult... |
I have an RSA signature of 1024 bit where i know the following:
1. Public modulus N
2. Public exponent (0x03)
3. Cypher message
Summary:
--------
An MD5 hash is calculated from a collection of byte and is used as message (M).
Having an hash that is a perfect cube forge a signature accepted as valid will... |
I really like this question, and have two things to say.
First note that CBC-MAC is no good since given the key it's easy to find a collision. Let $t$ be a tag for a message $m=m_1,m_2$ of length $\ell$ bits. Then, in CBC-MAC the input to AES first is $\ell$ and then the output is XORed with $m_1$ and input to AES, ... |
Wouldn't encrypting a message with AES, then encrypting the (randomly generated) AES key and IV with the EC public key suffice?
What attack vectors does ECIES protect against, that an AES-then-EC-encrypt wouldn't? |
Why is ECIES complex? |
Many AES-encrypted things (files, strings, database entries, etc.) start with ` "Salted__"` (`"U2FsdGVkX1"` in base64).
I hear it's some sort of OpenSSL interoperability thing: [a][1] [b][2] [c][3].
Is there some standard reference somewhere (perhaps an RFC?) that explains how such OpenSSL-inter-operable AES-encryp... |
So, here is the scheme of how this will look graphically:
[![GOST2 graphic model][1]][1]
The deal is to present distinguisher for this cipher.
First of all here is my drafts:
**Way 1**
Assume that distinguisher displays in constant time two plaintexts of _P_ and $\widehat{P}$ both consist of $P_1$ and $P_... |
Data is being encrypted in a database. A message digest is being created for deduplication purposes. Is it ok to use the message digest that will be the key of the table that houses the encrypted data as the initialization vector? Since the data is not being transmitted, just archived and retrieved locally, is this ... |
Is it bad practice to use the message digest of the plaintext as the initialization vector? |
Suppose $f=x_0x_2(x_1+1)+x_1x_3(x_0+1)$, annihilator is such function $g$, so that $gf=0$ for all $x$
Intuitively solution(for some reason) is obvious - $g=x_0x_1$, [which holds true][1]. (Cloud sagemath online script)
It bugs me, that I can't explain this "intuitively". How to arrive at solution properly, not gu... |
> Wouldn't encrypting a message with AES, then encrypting the (randomly
> generated) AES key and IV with the EC public key suffice?
Yes it would suffice and is what is usally done. However for this to work you'd have to have a way to relieably convert a random integer to a curve point and back which isn't trivially... |
I recently installed an android app called Secret Space Encryptor and think I found a serious flaw in it.
Let me explain: This app provides a variety of different ciphers to use and I used Threefish 1024 to encrypt a test message with "Your Key" as the key.
I then saved the ciphertext to a text file using the export ... |
Encrypt with one cipher and decrypt with a different cipher? |
[I have an idea for a new kind of mobile phone lock screen.][1] When you first create your pattern, you put together a series of colors and compass directions from the following choices: Red, Blue, Yellow, Green, North, South, East, and West. They can be referred to by their first letter. This pattern is the secret I w... |
Is there a system where I can securely store a secret value and compare a semi-ambiguous input to it? |
Ok, here's my scenario. I do research with people about their illegal drug use, and for one project I'm doing surveys with them when they visit a needle exchange. So over time the same people get repeatedly surveyed as they visit the exchange many times over. In order to link together multiple surveys from the same ... |
One way matchable hash? |
> Wouldn't encrypting a message with AES, then encrypting the (randomly
> generated) AES key and IV with the EC public key suffice?
Yes it would suffice and is what is usually done. However for this to work you'd have to have a way to reliably convert a random integer to a curve point and back which isn't trivially... |
when we generate DH parameters file in PEM format, like this:
```
-----BEGIN DH PARAMETERS-----
MCYCIQDyl7rfGI2GywHp7JC7juWhv3VL+skipzl/329sQCEBQwIBAg==
-----END DH PARAMETERS-----
```
or
```
-----BEGIN DH PARAMETERS-----
MIGHAoGBAdilyft4T5FJO0xga8hzoBcUmAZRTlxE930Dfda4LaC8TFsQkibgUYPJ
AuFWuAnKgjWjLH80Pt1shil... |
What are the first 4 and last 2 bytes in DH parameter files? |
I recently started studying cryptography and got interested in the subject. But I got this doubt when I was studying the encryption scheme. Even though we encrypt our message and change it into ciphertext, this ciphertext is still available to the attacker. So, what if the attacker modifies this ciphertext and sends it... |
> So, what if the attacker modifies this ciphertext and sends it to the receiver?
This is a real possibility considered by most encryption schemes.
> Then the receiver cannot decrypt the message right..?
Possibly, it depends on what exactly they changed. They could easily send something that decrypted as rand... |
> So, what if the attacker modifies this ciphertext and sends it to the receiver?
This is a real possibility considered by most encryption schemes.
> Then the receiver cannot decrypt the message right..?
Possibly, it depends on what exactly they changed. The attacker could easily send something that decrypted... |
For a block cipher
---
A block cipher is a PRP, a Pseudo Random Permutation. That is: given a key it generates a permutation of all possible plaintext blocks to all possible ciphertext blocks. So there is a bijection between each plaintext block and each ciphertext block, i.e. each possible plaintext block is assig... |
For a block cipher
---
A block cipher is a PRP, a Pseudo Random Permutation. That is: given a key it generates a permutation of all possible plaintext blocks to all possible ciphertext blocks. So there is a bijection between each plaintext block and each ciphertext block, i.e. each possible plaintext block is assig... |
I saw the key, create by OpenSSL, contains the following HEX string,
> 2a 86 48 86 f7 0d 01 01 01
Then the HEX string is interpreted as Object ID:
> 1.2.840.113549.1.1.1
It is obvious 01 01 01 is 1.1.1, but how does 2a 86 48 86 f7 0d be interpreted(parsed) as 1.2.840.113549?
|
How does 2a 86 48 86 f7 0d be interpreted as 1.2.840.113549? |
> So, what if the attacker modifies this ciphertext and sends it to the receiver?
This is a real possibility considered by most secure messaging schemes.
> Then the receiver cannot decrypt the message right..?
Possibly, it depends on what exactly they changed. The attacker could easily send something that dec... |
For a block cipher
---
A block cipher is a PRP, a Pseudo Random Permutation. That is: given a key it generates a permutation of all possible plaintext blocks to all possible ciphertext blocks. So there is a bijection between each plaintext block and each ciphertext block, i.e. each possible plaintext block is assig... |
I saw that an RSA key, created by OpenSSL, contains the following HEX string:
> 2a 86 48 86 f7 0d 01 01 01
that HEX string gets interpreted as Object ID:
> 1.2.840.113549.1.1.1
It is obvious 01 01 01 is 1.1.1, but how does 2a 86 48 86 f7 0d get interpreted (parsed) as 1.2.840.113549?
|
How is OID 2a 86 48 86 f7 0d parsed as 1.2.840.113549? |
At the moment I'm designing a crytosystem for a VPN server. One of the requirements is Perfect Forward Security, but I'n not sure how to implement authentication on the ephemeral key exchange.
If both parties possess a signed public key (signed by a CA or common trusted party) and exchange this, they can verify the ... |
At the moment I'm designing a crytosystem for a VPN server. One of the requirements is Perfect Forward Security, but I'n not sure how to implement authentication on the ephemeral key exchange.
If both parties possess a signed public key (signed by a CA or common trusted party) and exchange this, they can verify the ... |
**Question**: How to determine the RSA Private key size from the Public.key file? Just roughly, how big it could be?
$ ls -la Public.key
-rw-r--r--. 1 user user 498 Sep 4 15:31 Public.key
$
|
How to determine the RSA Private key size from the Public.key file? |
I want to design a scheme to encrypt a variable-length (but often short) message with a secret key, to provide confidentiality. The message is a human-readable text string with byte granularity. I prefer that the ciphertext is the same length as the plaintext (avoid padding).
Along the way, I also want to support in... |
How to propagate error in variable-sized message? |
I want to design a scheme to encrypt a variable-length message with a secret key, to provide confidentiality. The message is a short human-readable text string with byte granularity, let's say under 300 bytes. I prefer that the ciphertext is the same length as the plaintext (avoid padding).
Along the way, I also wan... |
I want to design a scheme to encrypt a variable-length message with a secret key, to provide confidentiality. The message is a short human-readable text string with byte granularity, let's say under 300 bytes. I prefer that the ciphertext is the same length as the plaintext (avoid padding).
Along the way, I also wan... |
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