instruction stringlengths 15 30k |
|---|
Digicipher and other proprietary systems? |
Don't think you've missed something.
> How do they keep these systems from being broken by someone just looking at the information in the smartcard that houses the key?
Those systems have indeed been (and frequently are) broken via Hardware reverse-engineering. Therefore I would chime in with your "not secure". ... |
What is significance of recovering the chaining value of a compression function, when the message and its output are known? in other words, if a compression function $CF$ takes a chaining value $h_{in}$ and a message $m$ as inputs and outputs $h_{out}$.
$h_{out}=CF(h_{in}, m)$
Is it a bad property if given $m$ an... |
From my point of view, multi-hashing will slow down things, but it won't add the security you are looking for in this case.
> Is cryptography able to solve this problem?
Yes. What you need is a message authentication code (MAC), which is a short piece of information used to authenticate a message and to provide i... |
From my point of view, multi-hashing will slow down things, but it won't add the security you are looking for in this case.
> Is cryptography able to solve this problem?
Yes. What you need is a message authentication code (MAC), which is a short piece of information used to authenticate a message and to provide i... |
From my point of view, multi-hashing will slow down things, but it won't add the security you are looking for in this case.
> Is cryptography able to solve this problem?
Yes. What you need is a message authentication code (MAC), which is a short piece of information used to authenticate a message and to provide i... |
If you want to be sure the value is not altered in transit by an active attacker that is occupying the wire then what you need is an integrity mechanism that will guarantee that nobody has tampered with the message. Such mechanisms are instantiated with the employment of a message authenticated code (MAC) which are bui... |
<h2> Diffie Hellman </h2>
[Diffie Hellman](http://en.wikipedia.org/wiki/Diffie-Hellman_key_exchange) is a key exchange protocol. It is an **interactive** protocol with the aim that two parties can compute a common secret which can then be used to derive a secret key used for some symmetric encryption scheme.
I t... |
What is the main reason (attacks) the appearance of the protocol SSL version 3.0 to replace version 2.0? |
What was the problem in the SSL version 2.0? |
I have a program (whereby people can download and run on their own computers) that will calculate a couple of unknown *values* each day. For simplicity sake, let's assume that the calculation is simply `Rand(0, 1)`. The program will run and the user will get a value e.g. `0.230957203975`.
He will then broadcast this... |
I have a program (whereby people can download and run on their own computers) that will calculate a couple of unknown *values* each day. For simplicity sake, let's assume that the calculation is simply `Rand(0, 1)`. The program will run and the user will get a value e.g. `0.230957203975`.
He will then broadcast this... |
What is the main reason (attacks) the appearance of the protocol SSL version 2.0 to replace version 3.0? |
I have a question which arised by analyzing the one-time pad cipher. I encrypt a binary sequence $a_1,a_2,..,a_N$ using a one-time pad with key sequence $k_1,k_2,k_3,...$, so I send $a_1+k_1, a_2+k_2,...a_n+k_N$.
Now I make mistake and instead of sending the above sequence I transmit $a_1+k_2,...,a_N+k_{N+1}$. Assum... |
Why is it foolish if you decide to use an RSA cipher to encode some message by first converting each letter of the message to an integer? So for exmaple Space=0, a=1, b=2,...
After the conversion I encrypt the integer $k$ as $k^e \mod N$.
I do not see why is there any difference? |
As I interpret it from your question, you suggest that you use RSA to encrypt a message $m$ interpreted as a string of characters?. Then a message $m=12$ could either be $m=ab$ or $m=\ell$? You need an unambiguous encoding.
What is done in practice is quite similar to your idea, but one interprets the entire mes... |
As I interpret it from your question, you suggest that you use RSA to encrypt a message $m$ interpreted as a string of characters? Then, for instance, an encoded message $k=12$ could either be $m=ab$ or $m=\ell$? You need an unambiguous encoding.
What is done in practice is quite similar to your idea, but one in... |
A hash function is a hash function: a deterministic, _public_ function with no secret parameter. Everybody can compute SHA-256, and they all get the same results when applied on the same inputs.
Therefore, if you give _H(m)_ to the attacker (who tries to recover _m_: a preimage attack), giving him _H(H(m))_ too does... |
Take a hash function `H()` to be something like SHA-256 and message `m`. If you are given `H(m)` and `H(H(m))`, can you use this info to help derive `m`?
Also interested in knowing how you analyze this problem to come up with your answer. |
Does having multiple hash iterations of the same message weaken your original message security? |
As a first note: No one would use RSA encryption to directly encrypt some plaintext (see below in the "practical advice"). Anyways, lets look at this:
As I interpret it from your question, you suggest that you use RSA to encrypt a message $m$ interpreted as a string of characters? Then, for instance, an encoded mess... |
As a first note: No one would use RSA encryption to directly encrypt some (possibly large) plaintext message (see below in the "practical advice"). Anyways, lets look at this:
As I interpret it from your question, you suggest that you use RSA to encrypt a message $m$ interpreted as a string of characters? Then, for ... |
Yes (guessing you are doing the cypher challenge?)
The "[Beaufort Decoder][1]" is a really good decoding tool (saves you time), then trial and error keywords. Also, the "[Vigenère cracking tool][2] can be used to find the length of the keyword. Paste the texts you're decoding; the number of the column(s) with the m... |
The encryption mode that I am using is CBC. Algorithm is AES and the key size is 128bit.
I will be encrypting a 36 byte string over 1.3 million times with the same key but with a random IV.
My question, as the title states, is it possible to reverse engineer the key for 1.3 million cypher texts without knowing the ... |
AES: Is it safe to encrypt same cleartext with same key but with million diferent IV? |
The encryption mode that I am using is CBC. Algorithm is AES and the key size is 128bit.
I will be encrypting a 36 byte string over 1.3 million times with the same key but with a random IV.
My question, as the title states, is it possible to reverse engineer the key for 1.3 million cypher texts without knowing the ... |
As a first note: No one would use RSA encryption to directly encrypt some (possibly large) plaintext message and RSA must not be used without a secure padding scheme (see below in the "practical advice"). Anyways, lets look at this:
As I interpret it from your question, you suggest that you use RSA to encrypt a mes... |
As a first note: No one would use RSA encryption to directly encrypt some (possibly large) plaintext message and RSA must not be used without a secure padding scheme (see below in the "practical advice"). Anyways, lets look at it:
As I interpret it from your question, you suggest that you use RSA to encrypt a messa... |
I'm writing an application for controlling computers from a client.
I'd very much like it if the connection is secure and only authenticated clients are allowed access.
The workflow will be something like this:
1. A client use decides to add the server
2. The server allows the client
1. Alternative 1; ... |
Java's `SecureRandom` is meant to be cryptographically secure, and I know part of that means that the output should not be usable to predict further output.
Though, admittedly, my knowledge in the area is limited, and I'd like to test the limits to get an idea of how secure Java's `SecureRandom` really is.
So let's... |
Java's SecureRandom & plaintext attack? |
A friend asked me the following, pointing out that the method is not very useful (my problem is I do not see why it is not good): Consider a person A which chooses $n$ as the public key for the Rabin cryptosystem. We want to be sure that we are communicating with person A so we send her a random item $r\equiv m^2 \mod ... |
A friend asked me the following, pointing out that the method is not very useful (my problem is I do not see why it is not good):
- Consider a person A which chooses $n$ as the public key for the Rabin crypto-system.
- We want to be sure that we are communicating with person A so we send her a random item $r\equi... |
Why is this authentication procedure using Rabin crypto not useful? |
It seems to me that what you need is a public-key [tag:signature] scheme like [tag:rsa] signatures.
The process would work something like this:
- A user license $L$ is created by your license generator
- Your system signs it to give $s(L)$ and the licence is $\{L,s(L)\}$.
When program tries to open the user... |
Let $p$ be a large public prime. Alice holds a private key $(e_1,d_1) \in Z_{p-1}^*$ such that $e_1 d_1 = 1 \mod {p-1}$. Bob also holds a different private key $(e_2,d_2)$ with the same property.
Let's say Alice wants to send a message $\large m \in Z_p^*$ to Bob:
$1.$ Alice computes and sends $\large m^{e_1} \mo... |
How can I break this encryption scheme? |
I am wondering whether an attacker can gain any useful information from having several hashes of an unknown plaintext that differs in relatively few bits. For example, if provided with:
H1 = SHA-256(TXT | 1)
H2 = SHA-256(TXT | 2)
...
HN = SHA-256(TXT | N)
Can an attacker recover `TXT` more easi... |
Is SHA-256 safe when used in this way? |
This answer has been updated a lot, again, after being accepted. I now base my analysis on simple functional equivalent source code to the deterministic PRNG used.
**The cryptosystem proposed works, in the sense that it allows decryption. The best cryptanalytic method there is to predict further output is enumeratin... |
This answer has been updated a lot, again, after being accepted. I now base my analysis on simple functional equivalent source code to the deterministic PRNG used.
**The cryptosystem proposed works, in the sense that it allows decryption. The best cryptanalytic method there is to predict further output is enumeratin... |
This answer has been updated a lot, again, after being accepted. I now base my analysis on simple functional equivalent source code to the deterministic PRNG used.
**The cryptosystem proposed works, in the sense that it allows decryption. The best cryptanalytic method there is to predict further output is enumeratin... |
I have a question which is related BB84 cryptosystem.
We are not able to send single photons so instead we send $K$ photons at a time all with the same polarization. An enemy can separate one of these from the remaining $K-1$.
If the enemy can detect the polarisation by only looking at one of the photons, the ot... |
I have a question which is related to [the BB84 cryptosystem](http://en.wikipedia.org/wiki/BB84).
We are not able to send single photons so instead we send $K$ photons at a time all with the same polarization. An enemy can separate one of these from the remaining $K-1$.
If the enemy can detect the polarisation b... |
Attack on BB84 algorithm for quantum key exchange? |
I am by no means a security expert but I am curious whether functions that don't produce different outputs when raised to the power of N (without any psuedorandomness) that are as strong as bcrypt or scrypt exist? |
This answer has been updated a lot, again, after being accepted. I now base my analysis on simple functional equivalent source code to the deterministic PRNG used.
**The cryptosystem proposed works, in the sense that it allows decryption. The best cryptanalytic method there is to predict further output is enumeratin... |
This answer has been updated a lot, again, after being accepted. I now base my analysis on simple functional equivalent source code to the deterministic PRNG used.
**The cryptosystem proposed works, in the sense that it allows decryption. The best cryptanalytic method there is to predict further output is enumeratin... |
I am by no means a security expert, but I am curious whether functions that don't produce different outputs when raised to the power of N (without any psuedo-randomness) exist, that are as strong as *"bcrypt"* or *"scrypt"*? |
This answer has been updated a lot, again, after being accepted. I now base my analysis on simple functional equivalent source code to the deterministic PRNG used.
**The cryptosystem proposed works, in the sense that it allows decryption. The best cryptanalytic method there is to predict further output is enumeratin... |
I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight.
The purpose is to encrypt my WiFi hotspot name with a key so that only my friends holding the key can decrypt a message from... |
One-time pad mistake in the transmission? |
I have a question which arised by analyzing the one-time pad cipher. I encrypt a binary sequence $a_1,a_2,..,a_N$ using a one-time pad with key sequence $k_1,k_2,k_3,...$, so I send $a_1+k_1, a_2+k_2,\dotsc,a_n+k_N$.
Now I make mistake and instead of sending the above sequence I transmit $a_1+k_2,...,a_N+k_{N+1}$. A... |
ASCII to same-length ASCII encryption? |
I know that there are elliptic curve groups, used in pairing-based cryptography, where the decisional Diffie Hellman problem (ie. given g, g^a, g^b and c, determine if c = g^ab) is easy but the computational Diffie Hellman problem (given g, g^a and g^b, find g^ab) is hard, and I know that if you can solve the discrete ... |
Are there groups where the computational Diffie Hellman problem is easy but the discrete log problem is hard? |
I know that there are elliptic curve groups, used in pairing-based cryptography, where the decisional Diffie Hellman problem (ie. given $g$, $g^a$, $g^b$ and $c$, determine if $c = g^{ab}$ is easy but the computational Diffie Hellman problem (given $g$, $g^a$ and $g^b$, find $g^{ab}$) is hard, and I know that if you ca... |
I use Rabin code with modulus $N$. Now assume that Alice sends me a message $m$ $(1\le m\le N)$ encoded by Rabin code. Unfortunately after Alice sent me the text I lose the information about the factorization of $N$ and therefore I cant decipher the message. I take new primes and construct a $\bar{N}>N$ and tell Alice ... |
I'm using SHA256 to hash the output of an entropy generator to generate random numbers. Is it generally better to treat the output of the entropy generator as single messages and hash each of those separately (internal state is reset), or as a message of unknown length (internal state is preserved)?
|
I use Rabin code with modulus $N$. Now assume that Alice sends me a message $m$ $(1\le m\le N)$ encoded by Rabin code. Unfortunately after Alice sent me the text I lose the information about the factorization of $N$ and therefore I cant decipher the message. I take new primes and construct a $\bar{N}>N$ and tell Alice ... |
This is hypothetical as I can't think of any reason to do this, but out of curiosity...
Could I, for example, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite broken, but getting close), to form a secure concatenated digest? Intuitively, I would think the chances of finding a coll... |
In a "Simple Power Analyse Attack", the difference in power consumption during multiply or square operation is used.
In the RSA decryption process with the "Square and Multiply" algorithm, both square and multiply operations are executed if bit value in key is $1$ and only square operation is executed if bit value ... |
I use Rabin code with modulus $N$. Now assume that Alice sends me a message $m$ $(1\le m\le N)$ encoded by Rabin code. Unfortunately after Alice sent me the text I lose the information about the factorization of $N$ and therefore I cant decipher the message. I take new primes and construct a $\bar{N}>N$ and tell Alice ... |
I'm working on software that should eventually result in a crypto file system similar to encfs. So far, i have a user password that goes through PBKDF2 using
PKCS5_PBKDF2_HMAC
with SHA-512 and a couple of thousand rounds to generate the Key Encryption Key. The Data Encryption Key and IV are random on a per-fi... |
I read the summary of deniable encryption on wikipedia:<br>
https://en.wikipedia.org/wiki/Deniable_encryption
Then I read a question, by `doom123` on security.SE:<br>
https://security.stackexchange.com/questions/34684/truly-deniable-encryption
But I had a subtly different problem which can be stated as follows:... |
I'm confused by your question.
I'm assuming you meant something like the following:
> Alice sends Bob a twice-encrypted message.
> Alice generates a fresh new symmetric key Ks,
> encrypts a plaintext message once with Ks,
> then encrypts the resulting data again using Bob's public key.
>
> Alice also "encrypts... |
I read the summary of deniable encryption on wikipedia:<br>
https://en.wikipedia.org/wiki/Deniable_encryption
Then I read a question, by `doom123` on security.SE:<br>
https://security.stackexchange.com/questions/34684/truly-deniable-encryption
But I had a subtly different problem which can be stated as follows:... |
Let $BW_N$ be a function such that $BW_N:\mathbb{QR}_{N} \mapsto \mathbb{QR}_{N}$ and let if be defined as follow: $BW_N(x) = x^2 \pmod N$ where $N=pq$ and p and q are primes and $p=q=3 \pmod 4$. I am reading on a set of lecture notes that, "$BW_N$ is a permutation over the squares mod N". Does someone know what that m... |
What does it mean that $BW_N$ is a permutation over the squares mod N? |
> "$BW_N$ is a permutation over the squares $\mod N$". Does someone know what that means?
You define your map $BW_N:\mathbb{QR}_N\rightarrow \mathbb{QR}_N$. Note that $$\mathbb{QR}_N:=\{r\in Z_N: r\equiv y^2 \pmod{N}, y\in Z_N\}$$ and a permutation is a one-to-one mapping (bijection).
Basically, this map is ... |
> "$BW_N$ is a permutation over the squares $\mod N$". Does someone know what that means?
You define your map $BW_N:\mathbb{QR}_N\rightarrow \mathbb{QR}_N$. Note that $$\mathbb{QR}_N:=\{r\in Z_N: r\equiv y^2 \pmod{N}, y\in Z_N\}$$ and a permutation is a one-to-one mapping from a set into the same set (bijection... |
> "$BW_N$ is a permutation over the squares $\mod N$". Does someone know what that means?
You define your map $BW_N:\mathbb{QR}_N\rightarrow \mathbb{QR}_N$. Note that $$\mathbb{QR}_N:=\{r\in Z_N: r\equiv y^2 \pmod{N}, y\in Z_N\}$$ and a permutation is a one-to-one mapping (bijection) from a set into the same se... |
In specific implementation we're using TLS 1.0, open ssl 0.9.8 but i'm referring to RFC 5246.
For performance reasons, I'm being asked if we can use TLS without encryption. The hope is that the perfomance cost of using TLS will be less. The implementation will retain authentication and integrity of communication... |
How can i accurately predict the next random number between 1 and 999, given past results. I have no knowledge of the prng or algorithm used. Is there a software that can find patterns from long strings of data? |
So my question is whether anyone knows of an efficient way to compute the neutral element (I'm gonna call it 1, but the operation doesn't have to be multiplication) in an abstract ring? More specifically, the scenario is this:
Suppose we have a ring $ (R,+,\cdot)$ (here, the operations are addition and multiplicatio... |
Efficiently computing the neutral element in a ring? |
does it make sense to hash a 22 byte secret (which may not have full entropy since it is chosen by the user) into a 512 bit hash (using Keccak-512)? Or to ask more precisely: Will the 512 bit hash still have full entropy even though the input is only 22 byte?
Best regards
|
Hash 22 byte secret into 512 bit hash: Full entropy? |
Does it make sense to hash a 22 byte secret (which may not have full entropy since it is chosen by the user) into a 512 bit hash (using Keccak-512)?
More precisely, will the 512 bit hash have full entropy even though the input is only 22 bytes? |
So my question is whether anyone knows of an efficient way to compute the neutral element (I'm gonna call it 1, but the operation doesn't have to be multiplication) in an abstract ring? More specifically, the scenario is this:
Suppose we have a ring $ (R,+,\cdot)$ (here, the operations are addition and multiplicatio... |
Would something like password hash verification work for this application?
* Assume you know long ahead of time the possible plaintext messages -- perhaps a selected set of [FourCC][1] codes or integers from 0000 to 9999.
* Assume you have enough storage in each consumer device to store ~20 bytes for each possible ... |
> "$BW_N$ is a permutation over the squares $\mod N$". Does someone know what that means?
You define your map $BW_N:\mathbb{QR}_N\rightarrow \mathbb{QR}_N$. Note that $$\mathbb{QR}_N:=\{r\in Z_N: r\equiv y^2 \pmod{N}, y\in Z_N\}$$ and a permutation is a one-to-one mapping (bijection) from a set into the same se... |
How can I accurately predict the next random number between 1 and 999, given past results. I have no knowledge of the PRNG or algorithm used.
How can I predict the next number of a long sequence of seemingly random numbers? Can I do it by hand, or should I use some kind of software to help find patterns from long s... |
How can i predict the next number of a long sequence of seemingly random numbers? |
Assume the following scheme for a PRNG generating decimals in [0,100)
Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag and convert to decimal notation. If the result is larger than 1,000,000, divide it by 10,000 and return it, other wise take the s... |
Assume the following scheme for a PRNG generating decimals in [0,100)
Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag and convert to decimal notation. If the result is smaller than 1,000,000, divide it by 10,000 and return it, other wise take the ... |
Assume the following scheme for a PRNG generating decimals in [0,100)
Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag and convert to decimal notation. If the result is smaller than 1,000,000, divide it by 10,000 and return it, other wise take the ... |
Assume the following scheme for a PRNG generating decimals in [0,100)
Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag and convert to decimal notation. If the result is smaller than 1,000,000, divide it by 10,000 and return it, other wise take the ... |
Assume the following scheme for a PRNG generating decimals in [0,100)
Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag and convert to decimal notation. If the result is smaller than 1,000,000, divide it by 10,000 and return it, other wise take the ... |
Assume the following scheme for a PRNG generating decimals in [0,100)
Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag. If the result is smaller than 1,000,000 in decimal, divide it by 10,000 and return it, otherwise take the subsequent 5 hexadecim... |
I am learning to use ECC. i get into situation where i have Q=abG, where G is the generator of the finite field formed on EC using a prime p modulus and a , b are random numbers.
now suppose i know Q, G and a , calculating bG=inverse(a)Q is efficient ? i know the order of the group too. i want to know whether this inv... |
I am learning to use ECC. i got into situation where i have Q=abG, where G is the generator of the finite field formed on EC using a prime p modulus and a , b are random numbers.
now suppose i know Q, G and a , calculating bG=inverse(a)Q is efficient ? i know the order of the group too. i want to know whether this inv... |
I am learning to use ECC. i got into situation where i have Q=abG, where G is the generator of the finite field formed on EC using a prime p modulus and a , b are random numbers.
now suppose i know Q, G and a , calculating bG=inverse(a)Q is efficient ? i know the order of the group too. i want to know whether this inv... |
Let's assume I've encrypted some text with some 24-byte key using 3DES ECB. Question: is it possible to regain the key if I have both encrypted and decrypted text? Excluding bruteforce. |
I am learning to use ECC. i got into situation where i have $Q=abG$, where $G$ is the generator of the finite field formed on EC using a prime $p$ modulus and $a$ , $b$ are random numbers.
now suppose i know $Q$, $G$ and $a$ , calculating $bG=\text{inverse}(a)Q$ is efficient ? i know the order of the group too. i want... |
Let be $C$ a code over the finite field $GF(2)$ with generator matrix $G$ and $H$ parity matrix. Let be $e+C=C'$ a coset of code $C$. Let be $S$ a non-singular matrix and $H'=H\times S$. Finally, let be $C''\subset C'$. Is posible find in efficient way any other element of the coset $C'$ **only** using $C''$ and $H'$ (... |
It is not practically possible. There are [several attacks][1] that are slightly faster than bruteforcing $2^{112}$ key candidates, but this is only a small factor. In some sense, they are bruteforce-like, since they require $2^{113}$ *smaller* steps.
[1]: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1... |
*Note that this question is somewhat similar to http://crypto.stackexchange.com/questions/5440/can-i-use-my-random-iv-for-aes-as-a-salt-for-pbkdf2/5441#5441*
My [current encryption format](https://github.com/RNCryptor/RNCryptor-Spec/blob/master/RNCryptor-Spec-v3.md) computes two random PBKDF2 salts (encryption and H... |
I am currently revising an [AES data format][1]. I would like to determine whether a provided password/key is incorrect. Previously this was done by validating the HMAC, but this makes it impossible to distinguish between data corruption and a bad password. It also requires reading the entire stream before validating t... |
I've discovered for myself that java's `BigInteger` is very slow, so I'm trying to weakly optimize [this java implementation of ed25519][1] which I will fork and post if successful by substituting `BigInteger` with jscience's [`LargeInteger`][2].
I'm almost done converting all of the `BigInteger`s to `LargeInteger`s... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.