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Why does Shamir Secret Sharing use Lagrange polynomials? |
How come Shamir Secret Sharing uses Lagrange interpolation? |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
I know session keys are exchanged (in SSL e.g.) over public-key cryptography channels but I was wondering if there are already known algorithms/methods for exchanging session keys over a symmetric-key channel? More specifically, is it possible/feasible to e.g. exchange 128-bit AES keys over a channel already using 128-... |
Exchanging session keys over symmetric-key channel? |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
I've read that Newton polynomials have better computational complexity, but Shamir's uses Lagrange polynomials instead. Does anyone know if there are particular reason why Newton polynomials aren't used instead? |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
Encrypt-then-MAC: full random keys or keys derived from master key? |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce the number database reads and compute new values on the fly. Suppose the use case involves a client `C` sending a server `S` a message and a number that `C` wanting appended to the messag... |
Is it a good idea to use Lagrange interpolation for encryption? |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce the number database reads and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message and a number that `C` wants to be appended to the... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce the number database reads and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message and a number that `C` wants to be appended to the... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce the number database reads and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message and a number that `C` wants to be appended to the... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce the number database reads and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message and a number that `C` wants to be appended to the... |
I'm pretty sure this is a really bad approach (in theory), but one of my clients is doing this and I was wondering… How bad it is to perform [tag:pbkdf-2] in this way (with 2000 iterations)?
a = PBKDF2(x, y)
b = PBKDF2(y, x)
x is the username (password in pbkdf2)
y is the password (salt in p... |
> Is it subject to some class of attacks or is it just a really bad crypto nightmare which is only subject to brute-force attacks?
You are calculating PBKDF2 twice, which takes twice as long. An attacker doing a brute force or dictionary attack only needs to calculate one of them to verify his guesses.
That means... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce database I/O and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message and a number that `C` wants to be appended to the message. `S`... |
With symmetric encryption, any key exchange protocol you run inside the encrypted channel must also be secure when run in plain text, if you want forward secrecy. That means you can only rely on the previously established keys for authentication (you are using authenticated encryption, right?), but not for hiding the n... |
With symmetric encryption, any key exchange protocol you run inside the encrypted channel must also be secure when run in plain text, if you want perfect forward secrecy. That means you can only rely on the previously established keys for authentication (you are using authenticated encryption, right?), but not for hidi... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce database I/O and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message `m` and a number `n` that `C` wants to be appended to `m` with... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce database I/O and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message `m` and a number `n` that `C` wants to be appended to `m` with... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce database I/O and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message `m` and a number `n` that `C` wants to be appended to `m` with... |
> Is it subject to some class of attacks or is it just a really bad crypto nightmare which is only subject to brute-force attacks?
You are calculating PBKDF2 twice, which takes twice as long. An attacker doing a brute force or dictionary attack only needs to calculate one of them to verify his guesses.
That means... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce database I/O and compute new values on the fly. Suppose the use case involves that a client `C` sends a server `S` a message `m` and a number `n` that `C` wants to be appended to `m` with... |
Is it a good idea to use Lagrange/Newtonian interpolation for encryption? |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
In the co... |
I am a bit confused. I just calculated manually the single steps of RSA for an implementation with small numbers and suddenly d was equal e. Please help! Heres my example:
1. I chose: q = 7 and p = 11
2. N = 77
3. phi(N) = 60
4. I chose: e = 29
5. e*d + k*phi(N) = 1
--> Extended Euclidean algorithm
k = ... |
I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption?
The goal is to reduce database I/O and compute new values on the fly. Suppose the use case involves that a client `C` sends to a server `S` a message `m` and a number `n` that `C` wants to be appended to `m` w... |
I am a bit confused. I just calculated manually the single steps of RSA for an implementation with small numbers and suddenly $d$ was equal $e$. Please help me understand what I am doing wrong.
Here’s my example:
1. I chose: $q = 7$ and $p = 11$
2. $N = 77$
3. $phi(N) = 60$
4. I chose: $e = 29$
5. $e \times ... |
Can someone kindly guide me from where can I get some simple explanation about attribute based encryption i.e. aside from the scientific papers? I was searching for a book or something that can help me in this regard but so far I have found none. Google also returns practically nothing aside from the papers.
Thank y... |
What is Attribute Based Encryption? |
What you are referring to is the same weakness in regard to malleability that is also applicable to (non-hashed schoolbook) RSA. In Elgamal an attacker can (in practice) not decrypt the transferred and encrypted message, but he can modify (factor) it and is able to determine the effect of his modification.
Let $y$ b... |
In HMQV, can one use multiple identities with one public key? |
Is it possible to get better randomness by using multiple PRNGs? |
**Update**: A general method is given by Elena Dubrova: [_A Scalable Method for Constructing Galois NLFSRs with Period $2^n-1$ using Cross-Join Pairs_][1], in IEEE Transactions on Information Theory, Volume 59, Issue 1 ([alternate link][2]). It gives an extensive bibliography of earlier constructs.
---
Other that t... |
Can someone explain what [attribute based encryption][1] is?
I was searching for a book or something that can help me in this regard but so far I have found none. Google also returns practically nothing aside from the papers.
[1]: http://en.wikipedia.org/wiki/Attribute-based_encryption |
**Update**: A general method is given by Elena Dubrova: [_A Scalable Method for Constructing Galois NLFSRs with Period $2^n-1$ using Cross-Join Pairs_][1], in IEEE Transactions on Information Theory, Volume 59, Issue 1 ([alternate link][2]). It gives an extensive bibliography of earlier constructs.
These constructio... |
I'm trying to prove that **definition 5** and **definition 6** in [this document][1] are equivalent. This is what I've done at the moment: Asume that the scheme has Indistinguishable encryptions in the presence of an eavesdropper (definition 5), then:
$$\mbox{Prob}[\mbox{Priv}_{\mathcal{A},\Pi}^{\mbox{eav}}(n)=1]=\m... |
this is normally seen in a typical SSL certificate. For the modulus, I know that it is represented in hexadecimal form, but why is there a semicolon (:) after every group of 2 digits?
Public-Key: (2048 bit) Modulus:
00:bf:e7:7c:28:1d:c8:78:a7:13:1f:cd:2b:f7:63:
2c:89:0a:74:ab:62:c9:1d:7c:62:eb:e8:fc:51... |
I was researching about hash, and I thought, If sites store passwords with hash algorithms, then can't this happen:
1. User A has the password 'hello'
2. User B finds out the hash code of the password of user A
3. User B knows the username of user A and uses hash collision to find a string with an identical hash
... |
Do sites store login password with hash? If so, can people can use hash collision to log in? |
I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a low collision rate to ensure low correlation between entities. A series of integers are input and a number of desired s... |
I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a low collision rate to ensure low correlation between entities. A series of integers are input and a number of desired s... |
I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a low collision rate to ensure low correlation between entities. A series of integers are input and a number of desired s... |
I am learning Hash Algorithms and in a presentation [ppt][1] about these algorithms I read that: `Length of h(m) much shorter then length of m`.
Now my question is:
What if we talk about an empty string, is it true that hash length is shorter than the length of message?
I searched in web and I found that: `The ... |
I have some encrypted texts (encrypted with 3DES in ECB mode without salt).
**My question: How can I decrypt them using a wordlist? (or without one)**
Example:
Encrypted text:
Xfi+h4Ir6l7zXCP+N4EPvQ==
The wordlist for this:
foo
bar
marketing
The original text was before encrypting was: "... |
> Do databases store the hash of the password or not? And if they do so, can the thing I wrote above happen?
Yes, and perhaps, but not likely. However, it is usually easier to find the original password rather than a collision. With a strong hash function, it is unlikely that you find another string with the same ha... |
I am learning Hash Algorithms and in a [presentation (PDF)][1] about these algorithms I read that:
> Length of $h(m)$ much shorter then length of $m$.
Now my question is:
What if we talk about an empty string, is it true that hash length is shorter than the length of message?
I searched the internet and ... |
I have some encrypted texts (encrypted with 3DES in ECB mode without salt).
**My question: How can I decrypt them using a wordlist? (or without one)**
Example:
Encrypted text:
Xfi+h4Ir6l7zXCP+N4EPvQ==
The wordlist for this:
foo
bar
marketing
The original text was before encrypting was: "... |
Please watch this video its very short.If you already know cryptography and really good at it please start from 3:51.
I didn't understood at 4:39 i someone here to explain ? How come
16^ 54 mod 17 is equal to
3 ^ (24*54) mod17 ≅ 1
He just wrote that. Alice didn't knew bob's private number how did he raised ... |
Please watch this [video](https://www.youtube.com/watch?v=3QnD2c4Xovk) its very short.If you already know cryptography and really good at it please start from 3:51.
I didn't understood at 4:39 i someone here to explain ? How come
16^ 54 mod 17 is equal to
3 ^ (24*54) mod17 ≅ 1
He just wrote that. Alice didn... |
Please watch this [video](https://www.youtube.com/watch?v=3QnD2c4Xovk) it's very short. If you already know cryptography and really good at it please start from 3:51.
I didn't understand the step at 4:39, can someone here to explain?
Why is $16^{54} \mod 17$ is equal to
$3 ^ {24\times54} \mod17 \equiv 1$?
... |
Informally, a signature scheme with message recovery is one where some or all of the message is embedded in the signature, allowing to conserve bandwidth when transmitting a signed message, compared to a signature scheme with appendix.
### Total message recovery
A _**signature scheme with total message recovery_*... |
Informally, a signature scheme with message recovery is one where some or all of the message is embedded in the signature, allowing to conserve bandwidth when transmitting a signed message, compared to a signature scheme with appendix.
### Total message recovery
A _**signature scheme with total message recovery_*... |
Informally, a signature scheme with message recovery is one where some or all of the message is embedded in the signature, allowing to conserve bandwidth when transmitting a signed message, compared to a signature scheme with appendix.
### Total message recovery
A _**signature scheme with total message recovery_*... |
Informally, a signature scheme with message recovery is one where some or all of the message is embedded in the signature, allowing to conserve bandwidth when transmitting a signed message, compared to a signature scheme with appendix.
### Total message recovery
A _**signature scheme with total message recovery_*... |
Informally, a signature scheme with message recovery is one where some or all of the message is embedded in the signature, allowing to conserve bandwidth when transmitting a signed message, compared to a signature scheme with appendix.
### Total message recovery
A _**signature scheme with total message recovery_*... |
I am doing a small project using elliptic curve in cryptography.My doubt is, can I direectly convert projective to jacobian co ordinate system without using the affine conversion in elliptic curve cryptography? Actually I am stuck with this point.
Thank you in advance...
|
How to convert projective to jacobian co-ordinate in ecc? |
I am doing a small project using elliptic curve in cryptography. My doubt is, can I directly convert a projective to a Jacobian coordinate system without using the affine conversion in elliptic curve cryptography? Actually, I am stuck at this point… |
How to convert projective to jacobian co-ordinate in ECC? |
Informally, a signature scheme with message recovery is one where some or all of the message is embedded in the signature, allowing to conserve bandwidth when transmitting a signed message, compared to a signature scheme with appendix.
### Total message recovery
A _**signature scheme with total message recovery_*... |
1: In normal ElGamal encryption, the encrypted message is a pair <code>(g<sup>b</sup>, g<sup>ab</sup>M)</code> - that is, the actual "encryption" is simply multiplication by the shared secret <code>g<sup>ab</sup></code>.
2: A common pattern with public-key encryption is to encrypt a symmetric key using PK, and then ... |
1. In normal ElGamal encryption, the encrypted message is a pair <code>(g<sup>b</sup>, g<sup>ab</sup>M)</code> - that is, the actual "encryption" is simply multiplication by the shared secret <code>g<sup>ab</sup></code>.
2. A common pattern with public-key encryption is to encrypt a symmetric key using PK, and then ... |
I've seen contradictory results. Sometimes hash functions are collision-resistant but not necessarily second-preimage resistant. I've seen this kind of things in papers from Bart Preneel.
How that can be possible ?
We have theorems that say that if a hash function is collision-resistant then it is second preimage... |
Does collision resistance imply (or not) second-preimage resistance? |
I've seen contradictory results. Sometimes hash functions are collision-resistant but not necessarily second-preimage resistant. I've seen this kind of things in papers from Bart Preneel.
[http://homes.esat.kuleuven.be/~eandreev/jips.pdf][1]
See the chapter "Other Domain Extenders".
How that can be possible ?
... |
I've seen contradictory results. Sometimes hash functions are collision-resistant but not necessarily second-preimage resistant. I've seen this kind of things in papers from Bart Preneel:
- “[Security Properties of Domain Extenders for Cryptographic Hash Functions][1]”
(See the chapter "Other Domain Extenders").... |
> Do databases store the hash of the password or not?
Yes, they do.
> And if they do so, can the thing I wrote above happen?
Perhaps it could, but it's unlikely. It is usually easier to find the original password rather than a collision. With a strong hash function, it is difficult to find another string with ... |
> Given that you use a SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that procedure in order to produce a secure MAC?
No, you don't need to do that, but you can.
> Needless to say a we'd still use a key, which we prepend or append to the message, but is that ... |
> Given that you use a SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that procedure in order to produce a secure MAC?
No, you don't need to do that, but you can.
> Needless to say a we'd still use a key, which we prepend or append to the message, but is that ... |
HMAC does nested hashing in order to prevent [Length Extension Attacks][1].
Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through [that][2] procedure in order to produce a secure MAC?
Needless to say we'd still use a key, which we prepend or ap... |
Is HMAC needed for a SHA-3 based MAC? |
> Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that procedure in order to produce a secure MAC?
No, you don't need to do that, but you can.
> Needless to say we'd still use a key, which we prepend or append to the message, but is that ... |
The [Rijndael specification][1] details the design choices for the s-box in section 7.2. They describe the choice of affine mapping as follows:
> We have chosen an affine mapping that has a very simple description per se, but a
complicated algebraic expression if combined with the ‘inverse’ mapping. It can be seen ... |
You need to know Key, IV, Padding and Operation Mode. Then you have to try all possible algorithms.
Without that (most likely very secret) information (Key, IV, Padding and Operation Mode) this is even more complex and hard to achieve than a know-plaintext attack. **To sum it up: its impossible.**
EDIT: As said, yo... |
How to find out the method used to encrypt the string `123456` which results in the value: `6g9SkDLIKa8l2VhafFnHvg==`? |
I am looking for a standard hash function which satisfies the following property:
A hash function $H(a,b) = F(h(a),h(b))$ with $h$ (within $F$) any standard cryptographic hash function and $F$ an associative function.
Is there any standard hash function(e.g. RIPEMD-160, SHA1) for which I can easily implement the ... |
If you don't need $H$ to be collision-resistant, you can use
$$H(a,b) = h(a) \times h(b) \bmod p$$
where $p$ is a large prime such that $p-1$ has a large divisor (and in particular, the discrete log problem modulo $p$ is hard), and with $h:\{0,1\}^* \to \mathbb{Z}/p\mathbb{Z}$ a hash function that outputs numbers... |
Many protocols use HMAC on messages that include a nonce, but they don't seem to do it in a consistent way. For example, in [OAuth][1] the nonce is in the middle of an URL-encoded key-value string, like this:
<pre>POST&http%3A%2F%2Fexample.com%2Frequest&a2%3Dr%2520b%26a3%3D2%2520q
%26a3%3Da%26b5%3D%253D%25253D%26c%... |
Is there a standard way to use a nonce with HMAC? |
I want to store files in a secure manner (i.e. no one should be able to decrypt the contents of the file without the secret key) but I also want a diff tool to be able to show me which lines changed (let's assume that you can't learn anything about the content of the file by seeing which lines have changed).
The ide... |
From a paper via Schneier on Security's [Another AES Attack][1] (emphasis mine):
> In the case of AES-128, there is no known attack which is faster than the 2<sup>128</sup> complexity of exhaustive search. However, **AES-192 and AES-256 were recently shown to be breakable by attacks which require 2<sup>176</sup> and... |
There are several kind of quantum key distribution (QKD) protocols as of today. Are you looking for a particular one?
The best known QKD protocol goes by the name BB84 after its inventors Bennett and Brassard and the year in which they presented their work. Searching on the Internet, I found this link http://fredhe... |
There are several kind of quantum key distribution (QKD) protocols as of today. Are you looking for a particular one?
The best known QKD protocol goes by the name BB84 after its inventors Bennett and Brassard and the year in which they presented their work. Searching on the Internet, I found this link http://fredhe... |
Theorem: Let y be a quadratic residue in Z_N* where N=pq. There are exactly four integers x_1, x_2, x_3 and x_4 where 0 < x_1 < x_2 < N/2 < x_3 < x_4 < N such that y = x_i^2 mod N for i =1,2,3,4.
The above theorem simply say that the exactly two of the four roots must be greater than N/2.
Most paper will state t... |
We have cryptography based on hard problems from number theory, like DDH.
When we speak about symmetric cryptography with AES, a mode of encryption (CBC, ...), what is the type of problem ? What is the term used ? |
Theorem: Let $y$ be a quadratic residue in $\mathbb{Z}_N$* where $N=pq$.
There are exactly four integers $x_1, x_2, x_3, x_4$ where $0 < x_1 < x_2 < \frac{N}{2} < x_3 < x_4 < N$ such that $y = x_i^2 \pmod{N}$ for $i=1,2,3,4$.
The above theorem simply states that exactly two of the four roots must be greater than ... |
We are planning to implement the time-stamping service(RFC 3161) using OpenTSA wanted to know
if OpenTSA supports PKCS-11 (Cryptoki)?
---------------------------------------
BTW: I did not find documentation or much information on OpenTSA.
It would be really helpful if you could comment on the support ... |
We are planning to implement the time-stamping service(RFC 3161) using OpenTSA wanted to know
if OpenTSA supports PKCS-11 (Cryptoki) to talk to HSMs?
---------------------------------------
BTW: I did not find documentation or much information on OpenTSA.
It would be really helpful if you could comment... |
I'm working with a third party protocol which employs AES-128 in ECB mode of operation to encrypt a packet composed of 16-byte blocks (it encrypts each block independently). I'm trying to determine if there are any reasonable attacks against the encryption.
One of the plaintext blocks it encrypts has a 4-octet nonce... |
We are planning to implement the time-stamping service ([RFC 3161](http://www.ietf.org/rfc/rfc3161.tx)) using OpenTSA wanted to know: ***Does OpenTSA support PKCS-11 (Cryptoki) to talk to HSMs?***
BTW: I did not find documentation or much information on OpenTSA. It would be really helpful if you could comment on the... |
Does OpenTSA support PKCS11 to talk to HSMs? |
I am currently working on a secure messaging website and I had been using RSA 2048 for encryption, decryption and signing of messages but I found it to be EXTREMELY LAGGY so i've moved to 1024.
I did a timing test and these are my results (this was a test of generating a private key from the same string in cryptico.... |
How do I choose the best $3\times3$ s-boxes? |
I'm developing a authentication and authorization protocol for a Bluetooth device. The device should communicate with an Android app and needs to be able to authenticate the app during the connection phase. Some kind of secret or asymmetric pair is therefore needed to be shared by the app and the Bluetooth device. As ... |
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