instruction stringlengths 15 30k |
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I'm working with Shor's algorithm and I have a question regarding the following step
$$a^r -1 = (a^{r/2}+1)(a^{r/2}-1)=0 \pmod n$$
Now what is going to be the result if $a^{r/2}$ was -1? this will mean it's going to be like this: $(1/a+1)(1/a-1)$ Will it also be $= 0 \pmod n$? |
I'm working with Shor's algorithm and I have a question regarding the following step
$$a^r -1 = (a^{r/2}+1)(a^{r/2}-1)=0 \pmod n$$
Now what is going to be the result if ${r/2}$ was -1? this will mean it's going to be like this: $(1/a+1)(1/a-1)$ Will it also be $= 0 \pmod n$? |
Any plaintext will do. If you choose 0x000..., then you can skip the XOR step entirely.
One extra step you can take to improve security is to periodically use the stream to choose a new AES key. This provides forward security: if an attacker manages to compromise the system (say, using a heartbleed-type exploit) and... |
what is perceptual Encryption and where we use it?
addition of definition ,I want some examples of using it. |
what is Perceptual Encryption? |
With block chipers can I assume that
Enc(k,Dec(k,m))=m
Meaning if I decrypt something with a key k and then encrypt the result with the same key k, do I get what I originally had? Using the same BC scheme of course.
I can't right? It's possible that it has some random parts, no?
|
Perceptual encryption is a term used to describe various encryption methods intended for audio, speech, image and video data.
The idea is that one performs encryption for multimedia content in a way that only a certain amount of "perceptual information" is touched by the encryption. It may be considered as intentio... |
What is "Perceptual Encryption", and where do we use it?
I came across it whilst reading a paper on ECC in a multimedia context, from which I quote:
> Hence, to achieve perceptual encryption, the higher-order biplanes were selected to be encrypted.
In addition to a formal definition, I would appreciate some ex... |
What is Perceptual Encryption? |
Is performing RSA encryption with the private key identical to performing RSA signature generation (signing)?
|
Is RSA encryption the same as signature generation? |
Is there an anonymous non-interactive authorisation scheme with peer-side auth. signature generation? |
I know the generic difference between a nonce and an IV. I am specifically looking for a clarification on these terms as used in the ["Evaluation of Some Blockcipher Modes of Operation"][1] by Phil Rogaway. In that when describing the block cipher modes for e.g. CBC he says the following (table in page 5) --
Confide... |
I know the generic difference between a nonce and an IV. I am specifically looking for a clarification on these terms as used in the ["Evaluation of Some Blockcipher Modes of Operation"][1] by Phil Rogaway. In that when describing the block cipher modes for e.g. CBC he says the following (table in page 5) --
> Confi... |
I have just made my own program to encipher, using AES in counter mode, and have validated it using NIST data. So I know I have done it properly.
I have read that AES-CTR can produce a stream of random numbers. To achieve this, what do I feed in as the plaintext? Will any text do? Does it matter if the plaintext has... |
**PLEASE NOTE:** The code I link to below has **not** yet been reviewed by anyone with professional cryptography experience. I expect that it contains bugs, and it is *definitely* not production-ready. I am still learning about the JCA; there are parts of the code I have not finished, and there are parts that I will mo... |
I would like to map integer values to points on Ed25519, and then back again.
Is there a technique that takes advantage of the specific structure of Ed25519?
|
Mapping integers to Ed25519 and back again? |
SHA1's compression function has two distinct parts: one where 16 words are expanded into 80 words, and one where the 80 words are used over 80 rounds. Are there specific names or terms for each of these parts, and if so, what are they? |
What are the two parts of SHA1's compression function called? |
I am reading on the [Ed25519 curve][1], and I am trying to understand a claim. Here is the claim:
> **Foolproof session keys**. Signatures are generated deterministically;
> key generation consumes new randomness but new signatures do not. This
> is not only a speed feature but also a security feature, directly
>... |
I am reading on the [Ed25519 curve][1], and I am trying to understand a claim. Here is the claim:
> **Foolproof session keys**. Signatures are generated deterministically;
> key generation consumes new randomness but new signatures do not. This
> is not only a speed feature but also a security feature, directly
>... |
Perceptual encryption is a term used to describe various encryption methods intended for audio, speech, image and video data.
The idea is that one performs encryption for multimedia content in a way that only a certain amount of "perceptual information" is touched by the encryption. It may be considered as intentio... |
Does anybody know an efficient mechanism to prove the possession of a digital signature (e.g. RSA) on a certain attribute (message) in zero-knowledge? That is, without revealing the actual signature (against tracking, for privacy) prove that you have one? Thanks a lot in advance! |
I've recently read a [question][1] about the irreducible polynomial behind the *subBytes()* operation in the Rijndael that has awakened and old curiosity I have:
Why $\,m(x)$ was chosen as $\,x^8+x^4+x^3+x+1$?
In the comments in the referenced question it has been mention that it was the first that fulfilled the ... |
> I'm not seeing any particularity between the two field that they build, but exists?
First off, one basic truth about finite fields is that there is at most one finite field of a given size. Assuming that both $x^7 + x + 1$ and $x^7 + x^4 + x^3 + x^2 + 1$ are both irreducible (I haven't checked), then they both ge... |
> I'm not seeing any particularity between the two field that they build, but exists?
First off, one basic truth about finite fields is that there is at most one finite field of a given size. Given that both $x^7 + x + 1$ and $x^7 + x^4 + x^3 + x^2 + 1$ are both irreducible, they both generate the same finite field... |
> I'm not seeing any particularity between the two field that they build, but exists?
First off, one basic truth about finite fields is that there is at most one finite field of a given size. Given that both $x^7 + x + 1$ and $x^7 + x^4 + x^3 + x^2 + 1$ are both irreducible, they both generate the same finite field... |
how can we prove that if there is a secure prg then P!=NP or in reverse order?(is there any reduction?) |
I run a baseball league and would like to do silent auctions for free agents. This would require teams to enter their highest bid and the highest bidder at the end of the auction period would win. Unfortunately, my league, my code, my server, I have access to the information if I choose to look at it. I'd like to no... |
Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext
[achilles:~/Arena/crypto] $ openssl enc -e -des -in plaintext -out encrypted1.bin
enter des-cbc encryption password:
Verifying - enter des-cbc encryption password:
[ac... |
Recently I've found the following work on the internet
http://ojs.academypublisher.com/index.php/jnw/article/viewFile/0508921928/2053
These guys have made a paper which claims to be an ECDSA blind signature however it seems that their scheme has a flow in it,
The process they describe is pretty standard:
-... |
Ecc blind signature scheme paper or an epic fail? |
Recently I've found the following work on the internet: [An ECC-Based Blind Signature Scheme](http://ojs.academypublisher.com/index.php/jnw/article/viewFile/0508921928/2053)
The paper claims to be an ECDSA blind signature however it seems that their scheme has a flaw in it,
The process they describe is pretty st... |
Is there a flaw in this ECC bling signature scheme? |
Recently I've found the following work on the internet: [An ECC-Based Blind Signature Scheme](http://ojs.academypublisher.com/index.php/jnw/article/viewFile/0508921928/2053)
The paper claims to be an ECDSA blind signature however it seems that their scheme has a flaw in it.
The process they describe is pretty sta... |
Is there a flaw in this ECC blind signature scheme? |
Wikipedia's [TLS article][1] says:
> The client responds with a ClientKeyExchange message, which may contain a PreMasterSecret, public key, or nothing. (Again, this depends on the selected cipher.) This PreMasterSecret is encrypted using the public key of the server certificate.
The parenthetical remark is intere... |
How is an X.509 public key used for TLS? |
Signature algorithms with elliptic curves have small output sizes compared to RSA for the same level of security.
What about the processing time to generate a signature ?
I've seen figures giving the advantage to RSA. That seems curious.
Leaving aside the implementation aspects, what could justify (in terms of... |
Signature algorithms with elliptic curves have small output sizes compared to RSA for the same level of security.
What about the processing time to generate a signature ?
I've seen figures giving the advantage to RSA. That seems curious.
Leaving aside the implementation aspects, what could justify (in terms of... |
[Skein](http://www.skein-hash.info/) is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as [“primary proposal”](https://www.schneier.com/skein.html).
Is there any advantage – other than potential memory or speed performance reasons – of picking a state size diffe... |
Is the following function is secure PRG?
G(x) = F(k,x) $\xor$ F(k,x $\xor 1^s$)
My solution - x $\xor 1^s$ = x' so G(x) becomes F(k,x)=f $\xor$ F(k,x')=f'. clearly f and f' are PRG i.e. generates random strings and $\xor$ of these will be random.
correct me if I am wrong. |
Is G is a secure PRG? |
Is the following function is secure PRG?
$G(x) = F(k,x) \oplus F(k,x \oplus 1^s)$
My solution - $x \oplus 1^s = x'$ so G(x) becomes $f \oplus f'$ with $f = F(k,x)$ and $f' = F(k,x')$. clearly f and f' are PRG i.e. generates random strings and $\oplus$ of these will be random.
Correct me if I am wrong. |
In RSA proof it can be proved that Z*(n) is closed under multiplication. Can it be also proved that Z(n) is closed under multiplication? If yes, then how? |
Given the RSA modulus $N$, currently, the best method to factor it is sub-exponent. But, now if I know the secret key $d$ of RSA, is that means I can factor $N$ efficiently?. It intuitively seems true as I know the public/private key pair. But I cannot prove this. Can someone help me to prove this ?(better provide the ... |
Is knowing the secret key of RSA equivalent to the factorization of $N$? |
In RSA proof it can be proved that $\mathbb{Z}^*_n$ is closed under multiplication. Can it be also proved that $\mathbb{Z}_n$ is closed under multiplication? If yes, then how? |
Given the RSA modulus $N$ the fastest method to factor it is of sub-exponent order. But, now if I know the private key $d$ of RSA, does that mean I can factor $N$ efficiently?. It intuitively seems true as I know the public/private key pair. Can someone help me to prove this?
Please provide references so that I can ... |
Is knowing the private key of RSA equivalent to the factorization of $N$? |
I would like to map integer values to points on Ed25519, and then back again.
Is there a technique that takes advantage of the specific structure of Ed25519?
|
Guillou and Quisquater ([link][1]) present a zero-knowledge proof of an RSA signature. Basically, the scheme is as follows:
Public knowledge: RSA modulus $n$, public RSA exponent $v$, preimage $X$.
Secret knowledge for prover: $A$, such that $A^v = X \mod n$.
$$
\begin{matrix}
\mathcal{P} & & \mathcal{V} \\
... |
how can we prove that if there is a secure **PRG** then **P!=NP** or in reverse order?(is there any reduction?)
a secure **PRG** is a pseudo random generator that for every eficient (running in probabilistic polynomial time) statistical test algorithm A , A cannot distinguish PRG from a truly random generator with a... |
If I have a private key of (`43`, `341`). What would be the steps I need to take to decrypt a small message using RSA? I have looked online and everything seems very confusing. Any tips or advice would be helpful.
I have gotten this far:
1. p=31 q=11
2. p*q=341
3. O(n)=(31-1)(11-1)=300
4. e=7
5. (43*e)%... |
Is container format relevant to security of encrypted message inside? |
As Ricky Demer mentioned, the [Shamir Secret Sharing Scheme][1] is information-theoretically secure ("crazy secure") and also, for the "trivial case" of "[all shares are necessary to recover the secret][2]", very simple.
We add all the shares together with "non-carrying addition", and the sum is decoded into the dec... |
Continued from http://crypto.stackexchange.com/questions/16021/is-there-a-flaw-in-this-ecc-blind-signature-scheme?noredirect=1#comment34029_16021
I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made one (I think).
Could you please verify my result... |
Continued from http://crypto.stackexchange.com/questions/16021/is-there-a-flaw-in-this-ecc-blind-signature-scheme?noredirect=1#comment34029_16021
I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made one (I think).
Could you please verify my result... |
From [Wikipedia][1]:
(1) Alice → Bob : g^x
(2) Alice ← Bob : g^y, E_K(S_B(g^y, g^x))
(3) Alice → Bob : E_K(S_A(g^x, g^y))
I know there should be something I'm missing, but I cannot think of why E_K(...) is used. Isn't the signature sufficient? Even if there was a MITM, having S_B(...) or S_A(...) is... |
In the STS Authentication Protocol, why are the signatures encrypted? |
I have read the post [Why should I use Authenticated Encryption instead of just encryption?][1] When is it safe to **not** use authenticated encryption?
I assumed hard drive volume encryption or per file encryption that is not transmitted over an insecure network should be considered safe to do without a MAC. Is tha... |
When is it safe to not use authenticated encryption? |
The encryption of the signatures
$\;$ keeps the identity of the initiator (Alice) confidential, even against active attackers
<br>$\;\;\;\;$ and<br>
$\;$ keeps the identity of the responder (Bob) confidential against passive eavesdroppers
<br>$\;\;\;\;$ and<br>
$\;$ provides some protection against [identity mis... |
Continued from http://crypto.stackexchange.com/questions/16021/is-there-a-flaw-in-this-ecc-blind-signature-scheme?noredirect=1#comment34029_16021
I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made one (I think).
Could you please verify my result... |
Continued from http://crypto.stackexchange.com/questions/16021/is-there-a-flaw-in-this-ecc-blind-signature-scheme?noredirect=1#comment34029_16021
#The problem
I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made one (I think).
Is there anyone w... |
Designing such signature schemes from scratch without having the security models in mind is likely to fail and very dangerous.
**Your proposed scheme**
Your verification relation is to check if: $sP - Q + R \stackrel{?}{=} zP + mP$ where $Q$ is the public key of the signer and lets call $hash$ simply $h$.
I ... |
Designing such signature schemes from scratch without having the security models in mind is likely to fail and very dangerous.
**Your proposed scheme**
Your verification relation is to check if: $sP - Q + R \stackrel{?}{=} zP + mP$ where $Q$ is the public key of the signer and lets call $hash$ simply $h$.
I ... |
Continued from http://crypto.stackexchange.com/questions/16021/is-there-a-flaw-in-this-ecc-blind-signature-scheme?noredirect=1#comment34029_16021
#The problem
I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made one (I think).
Is there anyone w... |
Designing such signature schemes from scratch without having strong experience is very likely to fail and very dangerous (see the tons of bad papers out there being accepted to "dubious" conferences and journals).
**Your proposed scheme**
Your verification relation is to check if: $sP - Q + R \stackrel{?}{=} zP ... |
Designing such signature schemes from scratch without having strong experience is very likely to fail and very dangerous (see the tons of bad papers out there being accepted to "dubious" conferences and journals).
**Your proposed scheme**
Your verification relation is to check if: $sP - Q + R \stackrel{?}{=} zP ... |
What Stephen says in the comment is correct. It is safe to not use authenticated encryption whenever your adversary model assumes that the attacker does not have the ability to manipulate ciphertexts.
>I assumed hard drive volume encryption or per file encryption that is not transmitted over an insecure network shou... |
Hi The "new" kind of ransomware invade your computer and crypt all your files using the RSA-2048...
Personnaly, I have been victim of cryptodefense: 40000 files encrypted...
I'm not going to pay anything to this *&?* but this is a big lost...
I have a lot of files in both form: crypted and uncrypted (backup from 201... |
Cryptodefense ransom use RSA-2048. Any chance with known plaintext attack? |
The "new" kind of ransomware invade your computer and crypt all your files using the RSA-2048.
Personally, I have been victim of cryptodefense: 40000 files encrypted...
I'm not going to pay anything to this *&?* but this is a big loss. I have a lot of files in both form: crypted and uncrypted (backup from 2011...)
... |
Given a secret K mod q which is shared among entities E1,...,En using polynomial shamir's secret sharing. How to share the inverse of k without revealing k and k^{-1} ? |
Given a secret $K \bmod q$ which is shared among entities $E_1,…,E_n$ using polynomial Shamir's Secret Sharing, how can the inverse of $k$ be shared without revealing $k$ and $k^{-1}$? |
Designing such signature schemes from scratch without having strong experience is very likely to fail and very dangerous (see the tons of bad papers out there being accepted to "dubious" conferences and journals).
**Your proposed scheme**
Your verification relation is to check if: $sP - Q + R \stackrel{?}{=} zP ... |
After reading many papers about [group signature schemes](https://en.wikipedia.org/wiki/Group_signature), I saw that basically all of them employ the possibility of "signature opening": The Group Manager (GM) can identify any signature made by his group's members. But I would like to completely eradicate that feature a... |
Well, there's always the generic option:
$\;$ the GM generates a common reference string for a stand-alone
<br>
$\;$ [computationally NIZK argument of knowledge](http://www0.cs.ucl.ac.uk/staff/J.Groth/NIZKJournal.pdf) system
$\;$ the GM generates a two inner key-pairs, one for a standard signature scheme
<br>
... |
Is the following function is secure PRG?
> Given F is a secure PRG and k is choosen random from key space K.
>
> $G(x) = F(k,x) \oplus F(k,x \oplus 1^s)$
My solution - $x \oplus 1^s = x'$ so G(x) becomes $f \oplus f'$ with $f = F(k,x)$ and $f' = F(k,x')$. clearly f and f' are PRG i.e. generates random strings ... |
As I understand, when you want to send a confidential message to someone, you encrypt the message with his public key. And he use his private key to decrypt the message.
At the same time, one can use his private key to sign a message, and other people use his public key to verify that it's him who sign it.
How th... |
Decrypt a public encrypted message and Sign a signature, how the math is different? |
Suppose we have a [one-way function](https://en.wikipedia.org/wiki/One-way_function) F(x) that exhibits the property F(a + b) = F(a) + F(b). Such a function could be used as a cryptographic primitive, no? |
Building cryptographic primitives using additive maps? |
In Elgammal cryptosystem, I was wondering should m (message) be less than p (large prime). Because on decryption, we are getting (m mod p). For (m mod p) to be equal to m shouldn't m be less than p. So what should be the size of p. Should it be a very very large prime number if I need to encrypt a file of 5 GB or somet... |
Size of p in Elgammal cryptosystem? |
Is it considered bad practice to use the same N and q parameters for all users in an SRP-6A based authentication system?
I know that q MUST be a Sophie Germain prime and N a safe prime, but can they be generated ahead of time and be somewhat fixed / hardcoded in the client and server? Or should I generate a fresh pa... |
I already found a protocol to find between two party who is richer (older), but Is there any protocol to find the youngest person among 3 parties, without revealing actual ages? |
Why can't you simply ask the person who made that file to tell you the password?
No one knows how to decode an AES-encrypted file, such as password-protected WinRar files, without knowing the password.
As far as we know, the only way to decode AES-encrypted files is to somehow obtain the right password, and then ... |
How to model a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$?
(Assume $\mathbb{G}_1$ and $\mathbb{G}_2 $ to be additive and multiplicative groups of prime order $q$)
Normally, for a $H: \mathbb{G}_1 \rightarrow \mathbb{G}_1$, we would model it as something like as follows
- pic... |
On modeling a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$? |
How can one model a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$?
(Assume $\mathbb{G}_1$ and $\mathbb{G}_2 $ to be additive and multiplicative groups of prime order $q$.)
Normally, for a hash $H: \mathbb{G}_1 \rightarrow \mathbb{G}_1$, we would model it as something like as follo... |
There might be better ways to do this, but I wanted to do it with only primitives found in [VIFF](http://viff.dk) (why? because it is the MPC framework I am most familiar with). There could be specialized protocols which are better.
In VIFF, we have access a primitive >= which returns 0 or 1 (false or true). We can ... |
C=E(D(E(P,K1),K2),K1)
For a chosen plaintext attack, given plaintext P, we compute the result of D(E(P,K1),K2) and store it as a table of length 2^112, then decrypt the cipertext C using 2^56 possible K1. I think we also have a meet-in-the-middle attack here; and the computation complexity is also 2^56 as in DES. Is... |
Why Triple DES is free from meet in the middle attack? |
How many keys are required for secure communication among 1000 person if
1.symmetric key encryption algorithm is used?
2.asymmetric key encryption algorithm is used?
My guess: For symmetric they each need to maintain and transfer their own key, so probably 1000*1000, and for asymmetric maybe just 2000, ea... |
I know that the private and public key in assymetric cryptography are different and the public is used for encryption while the private for decryption. My question is if they are symmetrical to each other in a mathematical way? They must be because the one is inverting what is done by the other.
|
How many keys are required for secure communication among 1000 person if
1. Symmetric key encryption algorithm is used?
2. Asymmetric key encryption algorithm is used?
My guess: For symmetric they each need to maintain and transfer their own key, so probably 1000*1000, and for asymmetric maybe just 2000, each... |
Well, there's always the generic option:
- the GM generates a common reference string for a stand-alone
[computationally NIZK argument of knowledge](http://www0.cs.ucl.ac.uk/staff/J.Groth/NIZKJournal.pdf) system
- the GM generates a two inner key-pairs, one for a standard signature scheme
and one for an... |
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