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How does a user register his verifier at host in SRP (Secure Remote Password) protocol? |
Isogeny based cryptography is one of the newest post-quantum cryptography. Hardness of this system is based on finding isogeny between two elliptic curves. Also this is theorem:
>Elliptic curves are isogenous over $F_p$ if and only if they have equal
number of points.
Recently, isogeny based public key methods a... |
Isogeny based cryptography is one of the newest post-quantum cryptography. Hardness of this system is based on finding isogeny between two elliptic curves. Also this is theorem:
>Elliptic curves are isogenous over $F_p$ if and only if they have equal
number of points.
Recently, isogeny based public key methods a... |
As per specifications document,
"*We have the natural restriction that at least two characters must be ciphered, i.e. b ≥ 2*"
where each character is represented by an integer of certain cardinality. So basically a 2 integer array is the minimum.
However say I want to encrypt a single input integer but restr... |
Can BPS be used to encrypt a single integer? |
How can you determine the largest plaintext block size and smallest ciphertext size if you used RSA with n=59768553302699443 using an alphabet with 27 characters? |
We intend to encrypt certain values in a database which holds personal information such as addresses so as to prevent data leakage should the database be compromised.
The intention is that each field is individually encrypted with AES GCM with a 128-bit key and 128-bit randomly generated nonce. Fields will generally... |
As per specifications document,
"*We have the natural restriction that at least two characters must be ciphered, i.e. $b \geq 2$*"
where each character is represented by an integer of certain cardinality. So basically a $2$ integer array is the minimum.
However say I want to encrypt a single input integer bu... |
We intend to encrypt certain values in a database which holds personal information such as addresses so as to prevent data leakage should the database be compromised.
The intention is that each field is individually encrypted with AES GCM with a 128-bit key and 128-bit randomly generated nonce. Fields will generally... |
how to do padding to input giving to encrypt using AES algorithm if the input is less than 128 bits?
i need to encrypt a number like 10 i.e,decimal value how to encrypt a decimal value please give me a valid answer |
I have been using the openssl function for encrypting data with AES-256-CBC in php. I have been able to encrypt it using an unique IV (by generating with openssl_random_pseudo_bytes)for each new encryption.
But I am struggling with the idea of authenticated encryption with aes cbc. How do I basically authenticate w... |
How to correctly encrypt data with proper authentication using AES-256-CBC in php? |
Isogeny-based cryptography is one of the newest post-quantum cryptography. Hardness of this system is based on finding isogeny between two elliptic curves. Also this is theorem:
> Elliptic curves are isogenous over $F_p$ if and only if they have equal
number of points.
Recently, isogeny based public key methods ... |
what is the best attack here?
Ek(m)=DESk1(DESk2(m))⊕k3
thanks. |
What is the best attack here?
> $E_k(m)=DES_{k1}(DES_{k2}(m)) \oplus k3$ |
How can you determine the largest plaintext block size and smallest ciphertext size if you used RSA with $n=59768553302699443$ using an alphabet with $27$ characters? |
In IBE schemes, system parameters (q, G, F, eˆ, P, Q, T, H1). I don't know eˆ.
For example, in TypeA pairing,
type=a
q=98826429041171753291515535532523512299028170537954154869719707264887274916552228805607584116490046284509883309001532457986879277885241872021906840932513241346999389365188296460009947
h=32243626948... |
I am currently reading about the length extension attack on Flickr but not understanding what's going on there.
m = SECRET || data || padding` and `api_signature = md5(m)
The server sends `data` and `api_signature` to the attacker. The attacker now knows:
- `h = md5(m) = api_signature`
- `data`
- leng... |
How does the Flickr length extension attack work? |
> How can he do that? He could take `api_signature = h = md5(m)` and use it as the Initialization Vector of the hash function and hash the extra data and another padding. This is the idea behind the hash length_extension attack, isn't it?
Correct.
> My question: The `api_signature` will change then because it is ... |
How to do padding to input giving to encrypt using AES algorithm if the input is less than 128 bits? I need to encrypt a decimal number such as 10. |
How to encrypt a number using AES? |
In ChaCha20-Poly1305, I know that reusing a nonce loses confidentiality and integrity for all messages encrypted with the (key, nonce) pair.
However, is security affected for those messages encrypted with the same key but *different* nonces? |
What happens if a nonce is reused in ChaCha20-Poly1305? |
The AEAD construction for chacha20-poly1305 described in the [IETF proposal][1] encodes message lengths into the text that is to be hashed. The [newer proposal][2] goes further and pads associated data and plaintext to multiples of 16 bytes.
Can anyone explain what the purpose of that is? The chacha20-poly1305 imple... |
I am currently reading about [the length extension attack on Flickr][1] (pdf) but not understanding what's going on there.
m = SECRET || data || padding` and `api_signature = md5(m)
The server sends `data` and `api_signature` to the attacker. The attacker now knows:
- `h = md5(m) = api_signature`
- `dat... |
In general, after we design a secure cryptographic protocol and make sure that it is efficient (e.g. through complexity analysis) we implement it.
**Question 1:** Do we implement it for proof of concept?
**Question 2:** Do we impalement it to support our claim that the protocol is efficient? |
Why Do We Implement a Crypto. Protocol? |
The title looks strange but it is to deal with this situation.
The data we have should only be accessible by our end user and data administrators, not anyone else. Ideally, each user should have different encryption key.
Even with administrators, I wish only when two of them agrees, then they could access the da... |
In general, after we design a secure cryptographic protocol and make sure that it is efficient (e.g. through complexity analysis) we implement it.
**Question 1:** Do we implement it for proof of concept?
**Question 2:** Do we implement it to support our claim that the protocol is efficient? |
Why do we implement a protocol? |
I have a problem with this excercise:
----------
Let $G$ be a group of order a prime $q$ and let $g, h$, be two randomly selected
elements of $G$, whit $g,h\ne 1$. Consider the following hash function on
integers $x_1$ and $x_2$:
$H(x_1,x_2)=g^{x_1}h^{x_2} $
Show that the problem of finding a collision ... |
> Do we implement it for proof of concept?
Absolutely. It's very easy to miss vital points if no implementation exists. [W3C for instance doesn't even allow protocols to be standardized without reference implementation(s)](https://www.w3.org/participate/implementation).
Personally I would require an implementati... |
In IBE schemes, system parameters $(q, G, F, eˆ, P, Q, T, H_1)$. I don't know $eˆ$.
For example, in TypeA pairing…
type = a
q = 9882642904117175329151553553252351229902817053795415486971970726488727491655222880560758411649004628450988330900153245798687927788524187202190684093251324134699938936518829646... |
I have a problem with this exercise:
> Let $G$ be a group of order a prime $q$ and let $g, h$, be two randomly selected elements of $G$, with $g,h\ne 1$. Consider the following hash function on integers $x_1$ and $x_2$:
> $H(x_1,x_2)=g^{x_1}h^{x_2} $
> Show that the problem of finding a collision pair $(x_1',x... |
> Do we implement it for proof of concept?
Absolutely. It's very easy to miss vital points if no implementation exists. [W3C for instance doesn't even allow protocols to be standardized without reference implementation(s)](https://www.w3.org/participate/implementation). Furthermore, an implementation may show small... |
I assume the question is related to academic work: why do we implement a protocol if we already know how efficient it is by a complexity analysis? The answer depends very much on the type of protocol. However, the answer typically is that a theoretical complexity analysis usually does not suffice to understand the conc... |
Suppose i have a `crypto provider`, i.e: i give that provider some plaintext bytes and get the encrypted result.
I don't know the used encryption method, but i know it is using a block cipher and the Block cipher mode of operation is something behaving like ECB (every block is encrypted individually => 2 identical b... |
For a personal project, I'm building a password manager, based off the project in this syllabus from Stanford http://crypto.stanford.edu/~dabo/cs255/hw_and_proj/proj1.pdf
Since I don't exactly have to take the class for the credit and strictly follow the instructions, I've gone ahead and changed some things (like I ... |
In IBE schemes, the system parameters are $(q, G, F, eˆ, P, Q, T, H_1)$. I don't know $eˆ$.
For example, in type A pairing…
type = a
q = 9882642904117175329151553553252351229902817053795415486971970726488727491655222880560758411649004628450988330900153245798687927788524187202190684093251324134699938936... |
tl;dr: Case 2 and 3 aren't any appreciable degree more secure than Case 1.
I suspect that the issues people are having with SMT-based solutions is that these LCG problems are very under-constrained:
1. The high-bit of the XOR is always unconstrained.
2. The bitwise-negation of a valid XOR is always valid. Toge... |
I don't actually know what I'm talking about, so apologies if I get anything wrong. At the moment I have a password naming system for most of my online accounts that looks something like this: masterpassword + appname, where appname is the name of whatever service the password is for. ex. `$sickpass123$_SoundCloud` and... |
There are several different scenarios to consider. If you assume all the sites/apps do things right, use a strong password hash, stay uncompromised, then no one should be able to find your master password anyway (unless it is a very poor low entropy password). So how or whether it is combined at all does not matter.
... |
I don't actually know what I'm talking about, so apologies if I get anything wrong. At the moment I have a password naming system for most of my online accounts that looks something like this: masterpassword + appname, where appname is the name of whatever service the password is for. ex. `$sickpass123$_SoundCloud` and... |
My recommendation will be to use a stream cipher consisting of any block algorithm in CTR mode. You could use block ciphers like AES, or hash functions like BLAKE2.
Stream ciphers are very efficient and light weight, hence it is the preferred cipher for encrypting phone calls. It should be good enough for your proje... |
>Which techniques can I use?
The most ideal option is to use synchronous-stream ciphers. They are not only fast, but also let you retain the plaintexts length. The best pseudorandom number generator I know is AES-CTR.
And to answer your second question,
>How secure are these techniques as compared to the ones ... |
In general, after we design a secure cryptographic protocol and make sure that it is efficient (e.g. through complexity analysis) we implement it.
Questions:
1. Do we implement it for proof of concept?
2. Do we implement it to support our claim that the protocol is efficient? |
> Is there any problems from using the approach I am suggesting?
Yes, there are several.
First of all, some sites generate first time passwords, or even long time passwords. You may want to store those too. What if a site requires frequent updates?
If one password is reversed, you'd still loose confidentiality... |
> Which techniques can I use?
You can use AES(for a good grade of encryption) + FPE(for preserve length).
A system like encryption of credit card number.
Have a look [here][1]
[1]: http://web.cs.ucdavis.edu/~rogaway/papers/synopsis.pdf |
I am looking for a "partial" encryption/decryption algorithm.
Let's say I am encrypting the following List of IDs (long values) $[1,2,3,4]$ (with a secret key) to an encrypted string $e$, I would like to produce several keys **$k_1,k_2,...,k_n$**, which can decrypt just **a subset (some IDs)**.
For example:
... |
In IBE schemes, the system parameters are $(q, \mathbb{G}, F, \hat{e}, P, Q, T, H_1)$. I don't know $\hat{e}$.
For example, in type A pairing…
type = a
q = 988264290411717532915155355325235122990281705379541548697197072648872749165522288056075841164900462845098833090015324579868792778852418720219068409... |
I don't actually know what I'm talking about, so apologies if I get anything wrong. At the moment I have a password naming system for most of my online accounts that looks something like this: masterpassword + appname, where appname is the name of whatever service the password is for. ex. `$sickpass123$_SoundCloud` and... |
Someone posted this on reddit a few days ago, and I haven't found much about it except for links back to the same page. Here's the article
http://programmingpraxis.com/2016/01/19/rsa-encryption-backdoor/
And for a brief summary, essentially, it's possible to introduce a backdoor during RSA key generation. For exa... |
Is there any more information on this RSA backdoor? |
Someone posted this on reddit a few days ago, and I haven't found much about it except for links back to the same page. Here's the article
http://programmingpraxis.com/2016/01/19/rsa-encryption-backdoor/
And for a brief summary, essentially, it's possible to introduce a backdoor during RSA key generation. For exa... |
I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less central to the security, along with the capacity/rate. Consequently, I have been making and breaking toy permutations to bet... |
I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less central to the security, along with the capacity/rate. Consequently, I have been making and breaking toy permutations to bet... |
I have learnt that Linear Congruential Random Number Generators are not cryptographically secure - my understanding is that given an LCG of the form:
X_n = (aX_(n-1) + c) mod m
It is possible to predict future X_n given a number of past X_n (even without knowing a, c, m).
In most implementations however th... |
I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less central to the security, along with the capacity/rate. Consequently, I have been making and breaking toy permutations to bet... |
I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less central to the security, along with the capacity/rate. Consequently, I have been making and breaking toy permutations to bet... |
There are several different scenarios to consider. If you assume all the sites/apps do things right, use a strong password hash, stay uncompromised, then no one should be able to find your master password anyway (unless it is a very poor low entropy password). So how or whether it is combined at all does not matter.
... |
Commonly, Zero Knowledge Proofs based on the Hamiltonian Path or Cycle problems are given as follows:
1. The Prover has a graph $G$, for which he knows a Hamiltonian Path (or Cycle). $G$ is also known to the Verifier and constitutes the public key.
2. The Prover generates $G'$ which is isomorphic to $G$ via a permu... |
I found that there are quite some active research activities in a field named "physical layer security", with in particular some types of codes that apparently are different from those commonly treated in the conventional textbooks on coding theory. Could someone kindly say the relevance, if any, of that field to crypt... |
*Info for the following abbreviations: K is the shared key for encryption known by A and B. $N_a$ is a nonce created by A. The function f is the increment by 1 function.*
(1) A -> B: $E_K(N_A)$
So A encrypts a nonce with the shared key and sends it to B.
(2) B -> A: $E_K(f(N_A))$
B receives it, I think fi... |
Why would you increment a nonce? |
> My only idea is that B authenticates himself to A, because if A later decrypts it, A will see whether B was able to decrypt it. But why would you need to increment the nonce?
Correct, that's the idea.
If B didn't need to increment the nonce and just encrypted the same value, the message sent back would be the s... |
*K is the shared key for encryption known by _Alice and _Bob. $N_A$ is a nonce created by Alice. The function f is the increment by 1 function.*
(1) Alice -> Bob: $E_K(N_A)$
So Alice encrypts a nonce with the shared key and sends it to Bob.
(2) Bob -> Alice: $E_K(f(N_A))$
Bob receives it, I think first he... |
When would you increment a nonce and when not? |
I'm studying for a cryto exam and have run across this question which has stumped me.
What is wrong in the following algorithm for computing a hash function? Take a message M, generate a random private RSA key K. Encrypt M with K and take the first 240 bits of the result as a hash of M
Thank you |
What is wrong in the following algorithm for computing a hash function using RSA? |
*K is the shared key for encryption known by _Alice and _Bob. $N_A$ is a nonce created by Alice. The function f is the increment by 1 function.*
(1) Alice -> Bob: $E_K(N_A)$
So Alice encrypts a nonce with the shared key and sends it to Bob.
(2) Bob -> Alice: $E_K(f(N_A))$
Bob receives it, I think first he... |
*K is the shared key for encryption known by _Alice and _Bob. $N_A$ is a nonce created by Alice. The function f is the increment by 1 function.*
(1) Alice -> Bob: $E_K(N_A)$
So Alice encrypts a nonce with the shared key and sends it to Bob.
(2) Bob -> Alice: $E_K(f(N_A))$
Bob receives it, I think first he... |
I have been considering this question now for a week and I just cannot find an answer.
I understand that non-repudiation cannot be provided without data origin authentication but I cannot think of an application which satisfies that non repudiation is not necessary.
Can anyone suggest an example of an application... |
Is there an example of an application where data origin authentication is necessary but non-repudiation is not necessarily required? |
> My only idea is that B authenticates himself to A, because if A later decrypts it, A will see whether B was able to decrypt it. But why would you need to increment the nonce?
Correct, that's the idea.
If B didn't need to increment the nonce and just encrypted the same value, the message sent back would be the s... |
*K is the shared key for encryption known by _Alice and _Bob. $N_A$ is a nonce created by Alice. The function f is the increment by 1 function.*
(1) Alice -> Bob: $E_K(N_A)$
So Alice encrypts a nonce with the shared key and sends it to Bob.
(2) Bob -> Alice: $E_K(f(N_A))$
Bob receives it, I think first he... |
I'm studying for a cryto exam and have run across this question which has stumped me.
What is wrong in the following algorithm for computing a hash function?
- Take a message $M$,
- generate a random private RSA key $K$.
- Encrypt $M$ with $K$ and
- take the first 240 bits of the result as a hash of $M$
|
if the client and the server need to exchange keys and I can sniff it, wouldn't I be able to decrypt the data transported? |
How is SSL secure? |
The field of cryptography that you are looking for is called [Kleptography][1]. In kleptography, we are dealing with a setting where the device performing your cryptographic tasks is potentially malicious. Now this device tries to leak information to some attacker that allows this attacker to break the used cryptograph... |
Identity Based Encryption is covered under RFC 5091 (specifying the algorithm), 5408 (specifying data structures), and 5409 (using IBE with Cryptographic Message Syntax). However, every IBE implementation that I've seen and used are nothing more than glorified web-mail systems.
Do any existing IBE systems allow secu... |
Do any Identity-based Encryption Systems support messaging between domains? |
I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less central to the security, along with the capacity/rate. Consequently, I have been making and breaking toy permutations to bet... |
I have a case where it may be possible for an adversary to deduce the plaintext inputs that went into creating a AES-128-GCM encrypted message (there is good IV diversity across the encrypted messages, however)
This opens up the potential to expose a GCM "oracle" to the adversary who may additionally be able to adapti... |
In context SSL/TLS, reading up on various sites, I find forward secrecy in DH key exchange being linked to its *ephemeral* use i.e. DHE. I don't fully understand this link, where does following reasoning break?
If non-ephemeral use (plain DH) would not provide forward secrecy, and ephemerality refers to a new sessio... |
Commonly, Zero Knowledge Proofs based on the Hamiltonian Path or Cycle problems are given as follows:
1. The Prover has a graph $G$, for which he knows a Hamiltonian Path (or Cycle). $G$ is also known to the Verifier and constitutes the public key.
2. The Prover generates $G'$ which is isomorphic to $G$ via a permu... |
Let two n-bit integer is encrypted using some LWE public key cryptography. Now, we need to perform comparison (>=,==) operation homomorphically. How can we do this? Can anyone describe this with example? |
How can comparision like (>=,==) be done using homomorphic encryption? |
In context SSL/TLS, reading up on various sites, I find forward secrecy in DH key exchange being linked to its *ephemeral* use i.e. DHE. I don't fully understand this link, where does following reasoning break?
If non-ephemeral use (plain DH) would not provide forward secrecy, and ephemerality refers to a new sessio... |
I am trying to devise an encryption scheme such that an adversary can win the following game with probability at most 1/2 + \epsilon.
- Adversary gives challenger two plaintext messages m_1 and m_0
-Challenger chooses one the two at random and encrypts it and gives adversary the cipher
- Adversary determines w... |
Let two n-bit integer is encrypted using some LWE public key cryptography. Now, we need to perform comparison (`>=`,`==`) operation homomorphically. How can we do this? Can anyone describe this with example? |
I want to encrypt some data(text/voice/video) but it is essential that the size of the cipher data remains the same as the plain data.
Which techniques can I use, and how secure are these techniques as compared to the ones which increase the size of the data? |
> Which techniques can I use?
The most ideal option is to use synchronous-stream ciphers. They are not only fast, but also let you retain the plaintexts length. The best pseudorandom number generator I know is AES-CTR.
> How secure are these techniques as compared to the ones which increase the size of the data.... |
> Which techniques can I use?
You can use a system like the ones used for the encryption of credit card numbers: AES (for a good grade of encryption) + FPE (for preserve length).
Have a look at [“A Synopsis of Format-Preserving Encryption” by Phillip Rogaway][1] (PDF)
[1]: http://web.cs.ucdavis.edu/~rogaway/... |
I am trying to devise an encryption scheme such that an adversary can win the following game with probability at most $1/2 + \epsilon$.
- Adversary gives challenger two plaintext messages $m_1$ and $m_0$
- Challenger chooses one the two at random and encrypts it and gives adversary the cipher
- Adversary deter... |
Let $x,y,k$ are plain text, cipher text and key respectively. Also suppose $\operatorname{Enc}$ be the algorithm of encryption for block cipher with size $n$. So we have
$$\operatorname{Enc}_k(x)=y$$
We know that if $x,y$ are given finding $k$ for big $n$ is so hard. Now we change the problem:
Let $k$(with size $... |
I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less central to the security, along with the capacity/rate. Consequently, I have been making and breaking toy permutations to bet... |
Last year, a question concerning plaintext attacks was posted on [on this website][1]. I have no problem to see how to solve it when we are given two ciphertexts and $(c_1,c_2)$ and their corresponding plaintexts $(m_1,m_2)$. But, when I am to deal with the situation where $p$ is unknown it gets complicated. In this in... |
In reference to the LR-Oracle experiment in Lindell & Katz (Intro. to Modern Cryptography 2nd ed.) Definition 3.23 states a scheme $\pi = (Gen,Enc_K,Dec_K)$ is CPA secure for multiple encryptions if
$\begin{equation} \textbf{Pr}[\textbf{PrivK}_{\mathcal{A},\pi}^{LR-cpa}(n) = 1] \leq 1/2 + \textbf{negl(n)}\end{equa... |
In reference to the LR-Oracle experiment in Lindell & Katz (Intro. to Modern Cryptography 2nd ed.) Definition 3.23 states a scheme $\pi = (Gen,Enc_K,Dec_K)$ is CPA secure for multiple encryptions if
$\begin{equation} \textbf{Pr}[\textbf{PrivK}_{\mathcal{A},\pi}^{LR-cpa}(n) = 1] \leq 1/2 + \textbf{negl(n)}\end{equa... |
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