instruction stringlengths 15 30k |
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We do not have the specification of `prv_key_enc`, thus we can not answer with some level of certainty anything more than: the maximum size of its output, in bytes, is **at least 128**.
On thing is sure: **the term `prv_key_enc` is grossly non-standard**. Problem is _not_ that [Googling it][1] is circular. The main ... |
I'm not sure if I get your question correctly. Do you like to use a 256 bit curve to generate a (secret) key of this size and later drop 64 bits? If this is the case your 64 bits will be useless because you secret key will not have any relation with the public. Furthermore, in a magic case that this works, your field o... |
We <strike>do</strike> initially did not have the specification of `prv_key_enc`, thus we <strike>can</strike> could not answer with some level of certainty anything more than: the maximum size of its output, in bytes, is **at least 128**. Looks like the answer now is: **exactly 171** after Base64 encoding.
On thing... |
We <strike>do</strike> initially did not have the specification of `prv_key_enc`, thus we <strike>can</strike> could not answer with some level of certainty anything more than: the maximum size of its output, in bytes, is **at least 128**. Looks like the answer now is: **exactly 172** assuming standard Base64 encoding.... |
We <strike>do</strike> initially did not have the specification of `prv_key_enc`, thus we <strike>can</strike> could not answer with some level of certainty anything more than: the maximum size of its output, in bytes, is **at least 128**. Looks like the answer now is: **exactly 172** assuming standard Base64 encoding.... |
I'm not sure if I get your question correctly. Do you like to use a 256 bit curve to generate a (secret) key of this size and later drop 192 bits? If this is the case your 64 bits will be useless because you secret key will not have any relation with the public. Furthermore, in a magic case that this works, your field ... |
Some general categories that come to mind:
- Same functionalities from less extreme assumptions; in particular, from *falsifiable* ones. For example, the FE for Turing machines in GKPVZ requires SNARKs and extractable witness encryption, both of require less plausible "knowledge-type assumptions." See [Gentry/Wichs... |
Some general categories that come to mind:
- Same functionalities from less extreme assumptions; in particular, from *falsifiable* ones. For example, the FE for Turing machines in GKPVZ requires SNARKs and extractable witness encryption, both of require less plausible "knowledge-type assumptions." See [Gentry/Wichs... |
Some general categories that come to mind:
- Same functionalities from less extreme assumptions; in particular, from *falsifiable* ones. For example, the FE for Turing machines in GKPVZ requires SNARKs and extractable witness encryption, both of require less plausible "knowledge-type assumptions." See [Gentry/Wichs... |
We <strike>do</strike> initially did not have the specification of `prv_key_enc`, thus we <strike>can</strike> could not answer with some level of certainty anything more than: the maximum size of its output, in bytes, is **at least 128**. Looks like the answer now is: **the output is always exactly 128 bytes** _before... |
I was lucky enough to, by brute force, have found two different messages, whose `SHA-256` hashes collide in the first 9 hexadecimal characters, which are 36 bits, let's call this `hash-prefix`.
Given the `Birthday Problem`, I had to put together `2^18` or rather `2^(36/2)` hashes so the chance of success at finding... |
I'm developing the login part of my application and I was asking myself how to it right. My applications stores some users' data server-side and must be inaccessible from us, so all the content must be encrypted using AES-256 with a password derived from the user's login password and this key would never leave the user... |
I'm developing the login part of my application and I was asking myself how to it right. My applications stores some users' data server-side and must be inaccessible from us, so all the content must be encrypted using AES-256 with a password derived from the user's login password and this key would never leave the user... |
I'm developing the login part of my application and I was asking myself how to it right. My application stores some users' data server-side and must be inaccessible from us, so all the content must be encrypted using AES-256 with a password derived from the user's login password and this key would never leave the user'... |
So for the play fair case, the number of possible keys is : 26x26 = 676 possible keys
But if we consider the repeated letters, how many unique keys will the play fair have? I mean how will considering the redundant letters affect the number of possible keys? |
I'm developing the login part of my application and I was asking myself how to it right. My application stores some users' data server-side and must be inaccessible from us, so all the content must be encrypted using AES-256 with a password derived from the user's login password and this key would never leave the user'... |
I'm developing the login part of my application and I was asking myself how to do it right. My application stores some users' data server-side that must be inaccessible from us, so all the content must be encrypted using AES-256 with a password derived from the user's login password and this key would never leave the u... |
My best interpretation of [this question][1] is that Java's crypto API has been subverted to perform RSA signature using PKCS#1 v1.5 **encryption** padding.
Assume the signature $S$ of a message $M$ is obtained by:
- hashing $M$ using SHA-1, yielding the 20-byte $H$;
- generating a 105-byte uniformly (true) rand... |
Would reseeding a PRNG with the PRN from the previous generation have any effects whatsoever on the quality of the generated numbers; if so, does this depend on the PRNG used, or are the effects generally applicable to any algorithm?
Perhaps I'll enhance the question with some pseudo-code:
`firstSeed := get_seed... |
We <strike>do</strike> initially did not have the specification of `prv_key_enc`, thus we <strike>can</strike> could not answer with some level of certainty anything more than: the maximum size of its output, in bytes, is **at least 128**. Looks like the answer now is: **the output is always exactly 128 bytes** _before... |
I am given p = 4916335901 q = 88903 and am asked to show these are prime as well as q|(p-1) in DSA.
I am unsure on how to do this, what does q|(p-1) mean exactly? |
Given p and q of DSA how do you show they are prime? |
> I am given $p = 4916335901$, $q = 88903$ and am asked to show these are prime
To check whether a given integer $n$ is prime you have to check whether it is only divisible by $1$ and $n$, i.e., that it is not a composite integer. If you are given such an integer you can either [factor](http://en.wikipedia.org/wiki... |
I've read that one of the vulnerabilites of ecryptfs is leaks to swap memory, and that the solution is to encrypt swap. But even if swap is encrypted, it's still open until I reboot. I've also read in [this][1] answer, from the designer of the ecryptfs crypto, that "eCryptfs makes no special effort to prevent key proli... |
I have the function H(x) = x^2 (mod p) where p is a prime of length n bits and this function maps to the message x to a n-bit hash value H(x).
I need to find out if it is pre-image resistant, second pre-image resistant and/or collision resistant and if it isn't collision resistant, what are some simple colliding mes... |
I am given
p = 4916335901
q = 88903
and am asked to show these are prime as well as `q|(p-1)` in DSA.
I am unsure on how to do this, what does `q|(p-1)` mean exactly? |
I have the function $H(x) = x^2 (mod p)$ where $p$ is a prime of length n bits and this function maps to the message $x$ to a n-bit hash value $H(x)$.
I need to find out if it is pre-image resistant, second pre-image resistant and/or collision resistant and if it isn't collision resistant, what are some simple colli... |
I have the function $H(x) = x^2\bmod p$ , where $p$ is a prime of length n bits and this function maps to the message $x$ to a n-bit hash value $H(x)$.
I need to find out if it is pre-image resistant, second pre-image resistant and/or collision resistant; and if it isn't collision resistant, what are some simple col... |
In the classic description of Zero Knowledge Proof of Knowledge, Victor must wait outside the entrance to the cave while Peggy goes to the fork and choose a side. It's only once Peggy has entered a tunnel and is out of view that Victor comes at the fork and shout the side he wants her to come out from.
I am wonderin... |
Why Victor must not know which tunnel Peggy chooses? |
Would reseeding a PRNG with the PRN from the previous generation have any effects whatsoever on the quality of the generated numbers; if so, does this depend on the PRNG used, or are the effects generally applicable to any algorithm?
Perhaps I'll enhance the question with some pseudo-code:
firstSeed := get_s... |
a given elliptic curve $$x^3+17x+5 \mod 59$$
with point $p = (4,14)$ and $8p = (16,40)$
now I am trying to compute $xP = (11,44)$
Is there a mathematical method to compute $x$, or do I simply compute a lot of $x$'s and hope for the best? |
Given the elliptic curve
$$E:y^2 = x^3+17x+5 \mod 59$$
with point $P = (4,14)$, how do I find $x$ such that compute $x\cdot P = (11,44)$
Is there a mathematical method to compute $x$, or do I simply compute a lot of $x$'s and hope for the best?
If it helps, I know $8P = (16,40)$ |
According to the article ["Lest We Remember: Cold Boot Attacks on Encryption Keys"][1] there is a quick and dirty entropy test that can help to find possible AES Key Schedules in memory dumps. Although there are references to this algorithm in blogs of other famouse cryptographers (for example, [this post][2]), I haven... |
Ziv-Lempel is a data compression algorithm, so in general it doesn't protect your data. As for your question:
> More generally, how difficult is it for an adversary to distinguish two strings which have been Ziv-Lempel encoded but not encrypted?
An adversary just can decode two strings and compare them. Due to t... |
I'll keep my question short. If I keep handing out different codes generated by this function, will it be trivial to figure out the secret key?
secret_key = {random bytes}
function generate_code(parameters)
return sha256(parameters + secret_key)
I know little about these things. What I like a... |
(1) If you double encrypt secret data with two different algorithms. How does the attacker know if he already broke the 'first layer' of encryption?
(a) Is it possible to determine the encryption algorithm used by analyzing the cipher text?
(b) If you find out what algorithm was used does it give you the necessary in... |
I am reading through the AES specification and am not able to wrap my head around the multiplication definition (section 4.2). Sorry to refer to a spec but AES is the holy grail in crypto so I hope its not too much to ask.
Here are my questions -
1. In section 4.2 why is the modulo chosen as {01}{1b} which is 28... |
I am reading through the AES specification and am not able to wrap my head around the multiplication definition (section 4.2). Sorry to refer to a spec but AES is the holy grail in crypto so I hope its not too much to ask.
Here are my questions -
1. In section 4.2 why is the modulo chosen as `{01}{1b}` which is ... |
1. `011b` is a hexadecimal representation of the polynomial $m(X) = X^8 + X^4 + X^3 + X + 1$ (so you should never regard it as an integer). This polynomial has coefficients in the finite field $\mathrm{GF}(2)$, which is just the math-y way to say that its coefficients are in $\{0,1\}$:
hex | 0 1 1 b... |
1. `011b` is a hexadecimal representation of the polynomial $m(X) = X^8 + X^4 + X^3 + X + 1$ (so you should never regard it as an integer). This polynomial has coefficients in the finite field $\mathrm{GF}(2)$, which is just the math-y way to say that its coefficients are in $\{0,1\}$:
hex | 0 1 1 b... |
I am trying to understand how differential Cryptanalysis works. [Here][1] I read how to use differential cryptoanalysis for cracking FEAL4 cipher.
As I understood you cannot use the same differential for cracking all keys. For each round key, you need to use new differential. So my question is why?
[1]: http://... |
I am trying to understand how differential Cryptanalysis works. [Here][1] I read how to use differential cryptoanalysis for cracking FEAL4 cipher.
> The big gotcha with this process is that you cannot just reuse the above differential path to crack rounds 2 and 3. You must build new differential characteristics that... |
I understand that the word size is the internal "working package size" below the block size of a cryptographic hash function (and a block cipher), as each block is broken into words an than processed round-based. Does this size have any practical relevance when using that function? For instance do algorithms with 64b w... |
What is the practical relevance of the wordsize when using a Hash? |
After an answer [here][1], about generate elliptic curves, I've start thinking about the algorithm. The mentioned algorithm will produce curves in the Weierstraß Reduced Form (WRF) over finite fields:
> $y^2 = x^3 + ax +b$ with $a,b\in \mathbb{F}_p$
And this WRF is the representation used in the [NIST][2] (where ... |
cryptographically good random elliptic curves? |
I have a question about Pseudo Random Function.
Let $f:\{0,1\}^n×\{0,1\}^n → \{0,1\}^n$ be a secure PRF.
$F(k,x) = \big(f(k,x) - f(k,x-1)\big)\bmod2^{n}$ is a **secure** PRF? |
I have a question about Pseudo Random Functions.
Let $f:\{0,1\}^n×\{0,1\}^n → \{0,1\}^n$ be a secure PRF.
Define $F(k,x) = \big(f(k,x) - f(k,x-1)\big)\bmod2^{n}$.
Is $F$ is a **secure** PRF? |
Where can I download a database of RSA keys? |
I have a question about Pseudo Random Functions.
Let $f:\{0,1\}^n×\{0,1\}^n → \{0,1\}^n$ be a secure PRF.
Define $F(k,x) = \big(f(k,x) - f(k,x-1)\big)\bmod2^{n}$.
Is $F$ is a **secure** PRF?
---
Note: a more difficult variant of the question considers Pseudo Random Function families $\{0,1\}^m×\{0,1\}^n → ... |
I am writing an application in Java that will be using SHA-1 HMAC message authentication. From what I understand, a connection over HTTPS is considered secure enough to share a secret key in plain text, and there is little added benefit to hashing the key before sending it from the client to the server.
So, my im... |
What is the best way to share a shared secret key over HTTPS to be used for HMAC authentication? |
(1) If you double encrypt secret data with two different algorithms. How does the attacker know if he already broke the 'first layer' of encryption?
(a) Is it possible to determine the encryption algorithm used by analyzing the cipher text?
(b) If you find out what algorithm was used does it give you the necessar... |
I am trying to understand how an attacker knows when he has successfully decrypted a ciphertext for an assignment. As such, some pointers/hints for the following questions would be greatly appreciated.
1. If you double encrypt secret data with two different algorithms. How does the attacker know if he already broke ... |
I am writing an application in Java that will be using SHA-1 HMAC message authentication. From what I understand, a connection over HTTPS is considered secure enough to share a secret key in plain text, and there is little added benefit to hashing the key before sending it from the client to the server.
So, my im... |
I've often heard/read that AES key sizes 256 & 192 would be weaker than 128 or not stronger as expected from the size increase, but I've never seen a proof. How does one proof the strength of a Rijndael key size?
If I understand correctly, the main effect of having the key size different from the block size is on ... |
After an answer [here][1], about generate elliptic curves, I've start thinking about the algorithm. The mentioned algorithm will produce curves in the Weierstraß Reduced Form (WRF) over finite fields:
> $y^2 = x^3 + ax +b$ with $a,b\in \mathbb{F}_p$
And this WRF is the representation used in the [NIST][2] (where ... |
[Bitcoin][1] uses [SHA-256][2], [Base58Check][3], [ECDSA][4] ([Sep256k1][5]) and [RIPEMD-160][6] as the basis of its encryption (see this [article][7] for a short guide on how addresses are created).
I would like to create an iOS-based wallet app that offers reasonable security.
* OpenSSL is not available on iOS,... |
I'm thinking of implementing rainbow tables for a specific blowfish problem, but I have trouble thinking of the proper way to apply the original paper (and its application to hash functions) to blowfish.
Say we have a not too clever password hashing function, which just uses the password as a key to blowfish-encrypt... |
I have a question about Pseudo Random Functions.
Let $f:\{0,1\}^n×\{0,1\}^n → \{0,1\}^n$ be a secure PRF.
Define $F\big(k,x\big) = \Big(f\big(k,x\big) - f\big(k,(x-1)\bmod2^{n}\big)\Big)\bmod2^{n}$.
Is $F$ is a **secure** PRF?
---
Note: a more difficult variant of the question considers Pseudo Random Funct... |
I have a situation in which I need to combine a 32-bit datum, 'G', and a 64-bit datum, 'I', to produce a 64-bit datum. No two tuples with the same 'I' value will have the same 'G' value, and vice versa. Collision resistance must be very high (data corruption will result if not).
Technically, I don't need encryptio... |
I have a question about Pseudo Random Functions.
Let $f:\{0,1\}^n×\{0,1\}^n → \{0,1\}^n$ be a secure PRF.
Define $F\big(k,x\big) = \Big(f\big(k,x\big) - f\big(k,(x-1)\bmod2^{n}\big)\Big)\bmod2^{n}$.
Is $F$ is a **secure** PRF?
---
Note: a more difficult variant of the question considers Pseudo Random Funct... |
**Theorem.** (Barring any errors, which are certainly possible): Let $A$ be any adversary attacking $F$. As long as $A$ makes *fewer than $2^n$ queries*, there is an adversary $B[A]$ attacking $f$, making the same number of queries and running in (roughly) the same time such that the PRF advantage of $A$ is at most the... |
**Theorem.** (Barring any errors, which are certainly possible): Let $A$ be any adversary attacking $F$. As long as $A$ makes *fewer than $2^n$ queries*, there is an adversary $B[A]$ attacking $f$, making at most twice the queries of $A$ and running in (roughly) the same time such that the PRF advantage of $A$ is at mo... |
**Theorem.** (Barring any errors, which are certainly possible): Let $A$ be any adversary attacking $F$. As long as $A$ makes *fewer than $2^n$ queries*, there is an adversary $B[A]$ attacking $f$, making at most twice the queries of $A$ and running in (roughly) the same time such that
$
\mathsf{Adv}^{\mathsf{prf}}_F... |
Alice has a set $S$ of words. Bob has a set $T$ of words. They want to compute the intersection $S \cap T$ of their words, with the help of a semi-trusted third party Trent. Trent runs a central server. The server is normally well-intentioned and not malicious. However, we are concerned about the risk of server co... |
Tony Arcieri makes an interesting point in his [Imperfect Forward Secrecy](http://tonyarcieri.com/imperfect-forward-secrecy-the-coming-cryptocalypse) article which basically boils down to:
1. large entities such as NSA are storing encrypted internet traffic, also what's to stop smaller entities such as proxy owners ... |
Alice has a set $S$ of words. Bob has a set $T$ of words. They want to compute the intersection $S \cap T$ of their words, with the help of a semi-trusted third party Trent. Trent runs a central server. The server is normally well-intentioned and not malicious. However, we are concerned about the risk of server co... |
I am building an open source hardware system that will be used to control things over the internet. The system consists of a Base Station and Modules which use wireless communication at 2.4GHz to exchange data.
Now I have come to the point where I need to protect the transmitted RF data against re-transmission and d... |
Is this an acceptable implementation of ARC4 encryption for my system? |
I am building an open source hardware system that will be used to control things over the internet. The system consists of a Base Station and Modules which use wireless communication at 2.4GHz to exchange data.
Now I have come to the point where I need to protect the transmitted RF data against re-transmission and d... |
I have a situation in which I need to combine a 32-bit datum, 'G', and a 64-bit datum, 'I', to produce a 64-bit datum. No two tuples with the same 'I' value will have the same 'G' value, and vice versa. Collision resistance must be very high (data corruption will result if not).
Technically, I don't need encryptio... |
Is there a flaw in whole disk encryption vs volume or folder encryption? |
I had [this](http://www.ecs.umass.edu/~tbashir/timing_attack_rsa_theory.htm) nice reading about RSA timing attacks. I was wondering if this attack is feasible while *signing* with RSA and, if yes, how.
Other questions: How this kind of attack is applied with DH?
Talking about timing attacks in general, in which ... |
I have been reading about [“Timing Attacks on RSA: Revealing Your Secrets through the Fourth Dimension” by Wing H. Wong](http://www.ecs.umass.edu/~tbashir/timing_attack_rsa_theory.htm). I was wondering if this attack is feasible while *signing* with RSA and, if yes, how?
Also, how this kind of attack is applied wi... |
I have a situation in which I need to combine a 32-bit datum, `G`, and a 64-bit datum, `I`, to produce a 64-bit datum. No two tuples with the same `I` value will have the same `G` value, and vice versa. Collision resistance must be very high (data corruption will result if not).
Technically, I don't need encryptio... |
Does anyone know the purpose of the "purpose" byte in the PBKDF2 implementation in Crypto++? It appears that the PBKDF2 does not use this byte, but I want to make sure I am not setting the option to some stupid default.
Here is the [method signature][1].
If you look at line 42 of the [pwdbase.h][2] file, it seem... |
What is the "purpose" byte in Crypto++ PBKDF2? |
Given two arbitrary/random n-bit words, how could one best mix them to get one n-bit word for general crypto usages?
I suppose that one should have an adequate measure of goodness of the mix before being able
to answer that question. So I would like to first ask: If z=f(x,y) mod 2**n is the result of the mixing x a... |
How to best mix two arbitrary/random n-bit words? |
I'm reading [A Practical Public Key Cryptosystem Provably Secure against Adaptive Chosen Ciphertext Attack][1] and here define Semantic Security ...
> Semantic security, dened by Goldwasser and Micali [14], captures the intu-
ition that an adversary should not be able to obtain any partial information
about a mess... |
Semantic Security Active or Passive attacks? |
Given two arbitrary/random n-bit words, how could one best mix them to get one n-bit word for general crypto usages?
I suppose that one should have an adequate measure of goodness of the mix before being able
to answer that question. So I would like to first ask: If $z=f(x,y) \bmod 2**n$ is the result of the mixing... |
> Given two arbitrary/random n-bit words, how could one best mix them to get one n-bit word for general crypto usages?
There's no such thing as "general crypto usage". Whenever we combine two different values in crypto, we have specific properties in mind, depending on why we are combining them, and in what context... |
I'm reading [A Practical Public Key Cryptosystem Provably Secure against Adaptive Chosen Ciphertext Attack][1] and here define Semantic Security ...
> Semantic security, dened by Goldwasser and Micali [14], captures the intu-
ition that an adversary should not be able to obtain any partial information
about a mess... |
> Given two arbitrary/random $n$-bit words, how could one best mix them to get one $n$-bit word for general crypto usages?
There's no such thing as "general crypto usage". Whenever we combine two different values in crypto, we have specific properties in mind, depending on why we are combining them, and in what con... |
> Given two arbitrary/random $n$-bit words, how could one best mix them to get one $n$-bit word for general crypto usages?
There's no such thing as "general crypto usage". Whenever we combine two different values in crypto, we have specific properties in mind, depending on why we are combining them, and in what con... |
**Theorem.** (Barring any errors, which are certainly possible): Let $A$ be any adversary attacking $F$. As long as $A$ makes *fewer than $2^n$ queries*, there is an adversary $B[A]$ attacking $f$, making at most twice the queries of $A$ and running in (roughly) the same time such that
$
\mathsf{Adv}^{\mathsf{prf}}_F... |
Given two arbitrary/random $n$-bit words, how could one best mix them to get one $n$-bit word for general crypto usages?
I suppose that one should have an adequate measure of goodness of the mix before being able
to answer that question. So I would like to first ask: If $z=f(x,y) \bmod 2**n$ is the result of the mi... |
Given two arbitrary/random $n$-bit words, how could one best mix them to get one $n$-bit word for general crypto usages?
I suppose that one should have an adequate measure of goodness of the mix before being able
to answer that question. So I would like to first ask: If $z=f(x,y) \bmod 2**n$ is the result of the mi... |
**Theorem.** (Barring any errors, which are certainly possible): Let $A$ be any adversary attacking $F$. As long as $A$ makes *fewer than $2^n$ queries*, there is an adversary $B[A]$ attacking $f$, making at most twice the queries of $A$ and running in (roughly) the same time such that
$
\mathsf{Adv}^{\mathsf{prf}}_F... |
If all that's known about `(G,I)` is stated in the question, using a hash of the concatenation of G and I, truncated to 64 bits, is a reasonable option (and I see no better one). However the risk that there is at least one collision grows fast with the number $n$ of `(G,I)`. On the (reasonable) assumption that this has... |
If Linear Cryptanalysis exploits the fact that the plaintext and ciphertext are not completely unrelated, is the attack possible without having access to the plaintext? |
Linear Cryptanalysis - possible without plaintext? |
I'm pretty sure I understand how public/private key cryptography works. Anybody can encrypt a message using a well-known public key, but only the person who holds the private key can decrypt it.
My question concerns securely sending a message to multiple people. Say there are `n` public/private key pairs. Is there a... |
Do any one-key-of-many cryptographic schemes exist? |
I'm not sure what this attack model is called - it's not known-plaintext and also not quite cipher-text-only.
Say you have one hundred ciphertexts which you know are the result of encrypting exactly the same plaintext with one hundred different public keys. Is there any vulnerability here in terms of figuring out w... |
Are RSA or ECC vulnerable to an attack where the same (unknown) plaintext is encrypted with multiple public keys? |
I'm pretty sure I understand how public/private key cryptography works. Anybody can encrypt a message using a well-known public key, but only the person who holds the private key can decrypt it.
My question concerns securely sending a message to multiple people. Say there are `n` public/private key pairs. Is there a... |
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