instruction stringlengths 15 30k |
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I'm doing a college project about digital image stenography on MATLAB. So far i've been able to get the help i needed from cool guys on stackoverflow but i now need to make my algorithm more hard to detect. This is what i have so far:
-My main function reads 4 grayscale RGB 24-bit images and one RGB 24-bit image to ... |
The classical definition of hash functions (found in books) are OK, but when studying a little more there is a lot of notions that seem ambiguous (contradictory) to me :
- Sometimes we have hash functions that need a secret key $k$
- Certain papers that design hash functions speak about a family of hash functions... |
Are there algorithms for secure secret sharing such that the algorithm depends solely on the value being secured, relying on no randomness in its calculations.
If there aren't, is such an algorithm an impossibility? If there are, what are some examples?
I ask because I've come up with a secret sharing scheme (whi... |
Do deterministic secret sharing schemes exist? |
I'm doing a college project about digital image steganography on MATLAB. So far i've been able to get the help i needed from cool guys on stackoverflow but i now need to make my algorithm more hard to detect. This is what i have so far:
-My main function reads 4 grayscale RGB 24-bit images and one RGB 24-bit image t... |
Does anybody know if there's known vulnerabilities in KCDSA/EC-KCDSA?
I have been researching for the past few hours and I haven't found anything. Wikipedia has very limited amount of information and based on the original whitepaper everything is rosy as expected. |
The parameter $k$ appeared in the definitions of hash functions, since many properties are difficult to formulate for a single concrete hash function. For instance, what would it mean that SHA-256 is collision resistant? Clearly, there are values that collide, and there exists a very short algorithm that outputs a coll... |
<a href="http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf">The Galois/Counter Mode of Operation (GCM)</a>
This paper describe using GCM mode with 128-bit and 64-bit block cipher. Can we use this mode for 256-bit and 512-bit block cipher? |
You could, however the one part that doesn't translate in an obvious manner is the Galois field representation; you would need to pick a field representation for $GF(2^{256})$ and $GF(2^{512})$, because those have not be predefined for those sizes.
Here's the issue; GCM does field multiplications internally; that is... |
My SSH server has a 2048-bit public key. But my private key, for clients to login, is 4096-bit.
In this case, do I have the brute force protection of 2048 or 4096 bits?
My worry is that someone could brute force the private key and login to the server. |
My public key is 2048 bits, but my private key is 4096. What is my effective security? |
It appears that based on your description, the server has a 2048 bit key pair and the clients logging in have 4096 bit key pairs.
>In this case, do I have the brute force protection of 2048 or 4096 bits?
For someone to impersonate one of your users, they would have to break the 4096 bit key.
For someone to im... |
My SSH server public key is 2048 bits, but my account's private key is 4096. What is my effective security? |
It appears that based on your description, the server has a 2048 bit key pair and the clients logging in have 4096 bit key pairs.
>In this case, do I have the brute force protection of 2048 or 4096 bits?
For someone to impersonate one of your users, they would have to break the 4096 bit key.
For someone to im... |
What are the implications of a curve having a non-integer co-factor for its generator point? Is that even possible? |
Does a cofactor of an elliptic curve have to be an integer? |
Any deterministic secret sharing scheme as in the question has the property that any participant can run the deterministic algorithm for a guess of the shared secret, and eliminate it if the share that the algorithm deterministically gives him/her does not match his/her share. This implies that either _some_ informatio... |
Any deterministic secret sharing scheme as in the question has the property that any participant can run the deterministic algorithm for a guess of the shared secret, and eliminate it if the share that the algorithm deterministically gives him/her does not match his/her share. This implies that _some_ information about... |
Any deterministic secret sharing scheme as in the question has the property that any participant can run the deterministic algorithm for a guess of the shared secret, and eliminate it if the share that the algorithm deterministically gives him/her does not match his/her share. This implies that _some_ information about... |
In a short paper "[On sharing secrets and Reed-Solomon codes][1]," _Communications
of the ACM,_ vol. 24, pp. 583-584, September 1981, Bob McEliece and I described
a secret-sharing system that uses no randomness (cf. the second paragraph of
the paper). This is most useful for very
large secrets (lots of bits) since ... |
There's the well-known question on whether to [sign or encrypt first](http://crypto.stackexchange.com/q/5458/2663). However, if instead a message is to be ring-signed such that either recipient could be the actual signer, is there any scheme that combines signing and encrypting in one "atomic" step? |
Is there a method to combine encryption and ring signing? |
Yes, like there are conventional [signcryption schemes](http://en.wikipedia.org/wiki/Signcryption) combining digital signatures with encryption into a single primitive, there are also **ring signcryption schemes** that realize the same for ring signatures and encryption. Look for instance [here](http://ro.uow.edu.au/cg... |
Yes, like there are conventional [signcryption schemes](http://en.wikipedia.org/wiki/Signcryption) combining digital signatures with encryption into a single primitive, there are also **ring signcryption schemes** that realize the same for ring signatures and encryption. Look for instance [here](http://ro.uow.edu.au/cg... |
I'm doing a college project about digital image steganography on MATLAB. So far i've been able to get the help i needed from cool guys on stackoverflow but i now need to make my algorithm more hard to detect. This is what i have so far:
- My main function reads 4 grayscale RGB 24-bit images and one RGB 24-bit image ... |
**SHA-512 truncated to 256 bits is as safe as SHA-256 as far as we know**. The NIST did basically that with SHA-512/256 introduced March 2012 in [FIPS 180-4][1] (because it is faster than SHA-256 when implemented in software on many 64-bit CPUs). SHA-224 is just as safe as using 224 bits of SHA-256, because that's basi... |
I am trying to implement the Fiat-Shamir identification protocol, however the end results always fail to match. I am using algorithm's description from [here][1].
Preparation:
1. Select 2 prime integers and their product:
n = 19 * 23 = 437
2. Select `s` coprime to `n`:
s = 242
3. C... |
I was trying to prove that a given function is not a one way function and I was not sure how to do it because maybe I had unclear what a one way function was (OWF).
The definition that I have for a OWF is the following:
Easy to compute for all inputs: for all PPT A (probabilistic polynomial time algorithms), A(x)... |
I am trying to implement the protocol mentioned in Section 3.4 of the following paper http://www.ece.umd.edu/~danadach/MyPapers/set-int.pdf in Java.
In the Second Step, the Client computes a polynomial of degree 'n' over the finite field.
For C = {1, 2}, will the Polynomial be x^2 - 3x + 2?
Can the polynomial ... |
We know reusing IV can compromise cipher-text secrecy.
Is that OK to use same key for encrypting unlimited plain-texts in authenticated encryption (GCM) and confidential only encryption (CTR) if we use random IV to encrypt each plain-text? or not a good idea? |
We know reusing IV can compromise secrecy.
Is that OK to use same key for encrypting unlimited plain-texts in authenticated encryption (GCM) or confidential only encryption (CTR) if we use random IV to encrypt each plain-text? or not a good idea? |
I am currently reading through *Cryptography Engineering* and came across this definition of block cipher security:
> Definition 2 An attack on a block cipher is a non-generic method of
> distinguishing the block cipher from an ideal block cipher.
Reading further, I find myself struggling to understand what the ... |
We know reusing IV can compromise secrecy.
Is that OK to use same key for encrypting unlimited plain-texts in authenticated encryption (GCM), or confidential only encryption (CTR) if we use random IV to encrypt each plain-text? Or is that a bad idea? |
I am currently reading through *[Cryptography Engineering][1]* and came across this definition of block cipher security:
> Definition 2 An attack on a block cipher is a non-generic method of
> distinguishing the block cipher from an ideal block cipher.
Reading further, I find myself struggling to understand what... |
I am trying to implement the protocol mentioned in Section 3.4 of “[Efficient Robust Private Set Intersection](http://www.ece.umd.edu/~danadach/MyPapers/set-int.pdf)” in Java.
In the Second Step, the Client computes a polynomial of degree $n$ over the finite field.
For $C=\{1,2\}$, will the Polynomial be $x^2-3x+... |
I am currently reading through *[Cryptography Engineering][1]* and came across this definition of block cipher security:
> Definition 2 An attack on a block cipher is a non-generic method of
> distinguishing the block cipher from an ideal block cipher.
Reading further, I find myself struggling to understand what... |
We know reusing IV can compromise secrecy.
Is that OK to use same key for encrypting unlimited plain-texts in authenticated encryption (GCM), or confidential only encryption (CTR) if we use random IV to encrypt each plain-text? Or is that a bad idea?
Update: *We use AES as cipher* |
We know reusing IV can compromise secrecy.
What's different between IV and nonce in CTR or GCM mode? (i know there is a counter nonce 001 002 003 .. but there is a random IV before counter number to encrypt each block and some experts in comments are saying we have no IV in CTR or GCM mode ?! i think the right word... |
We know reusing IV can compromise our secrecy. here are my questions:
1-is that OK to use the same key for encrypting plain-texts in authenticated encryption (GCM), or confidential only encryption (CTR), if we use random IV to encrypt each plain-text? and how many time we can reuse same key to encrypt plain-text ?
... |
We know reusing IV can compromise our secrecy. I have some questions aiming to clarify the use of an IV/Nonce in CTR/GCM:
1. Is it OK to use the same key for encrypting plain-texts in authenticated encryption (GCM) and confidential only encryption (CTR) if we use a random IV to encrypt each plain-text? How many time... |
1. Haven't written up an answer to this
2. Not answering this one right now either
3. [This question is a duplicate of point #3 and has a good answer](http://crypto.stackexchange.com/questions/1849/why-not-use-ctr-with-a-randomized-iv?rq=1) |
1. Yes, as long as you obey all the total usage limits and choose the IV appropriately (see below).
2. Whilst IV is a general term for any initialisation vector the recent trend has been to use the term 'IV' to refer to a random vector, and "nonce" (a contraction of "**n**-umber used **once**") to refer to an input ... |
1. Yes, as long as you obey all the total usage limits and choose the IV appropriately (see below).
2. Whilst IV is a general term for any initialisation vector the recent trend has been to use the term 'IV' to refer to a random vector, and "nonce" (a contraction of "**n**-umber used **once**") to refer to an input ... |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
Who first published about the interest of more than two prime factors in RSA? |
Say for example I have a function called F defined as `F(x) = g^x mod p` where p is a 1024-bit prime and g is a generator of `Zp⇤`. The secret key r is chosen randomly from `Zp-�1`. The message is computed using a one-time pad. How do I decrypt the entire message after obtaining g, p, and the first 1024 bits of plainte... |
Say for example I have a RSA function called F defined as `F(x) = g^x mod p` where p is a 1024-bit prime and g is a generator of `Zp⇤`. The secret key r is chosen randomly from `Zp-�1`. The message is computed using a one-time pad. How do I decrypt the entire message after obtaining g, p, and the first 1024 bits of pla... |
Say for example I have a RSA function called F defined as `F(x) = g^x mod p` where p is a 1024-bit prime and g is a generator of `Zp⇤`. The secret key r is chosen randomly from `Zp-�1`. The message is computed using a one-time pad. How do I decrypt the entire message after obtaining g, p, and the first 1024 bits of pla... |
The coefficients in the polynomial are elements of the field; when you expand the polynomial:
$$(x-1)(x-2)$$
where $1$ and $2$ are field elements, the normal algebraic rules apply (because those rules are based on the field properties), you get:
$$x^2 + -(1+2)x + (1\times2)$$
where the middle coefficient is... |
I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r\ne 1$ is chosen randomly from $\mathbb Z_p^*$. The encrypted message is computed using a <strike>one-time pad</strike> st... |
I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ is chosen randomly from $\mathbb Z_p^*$. The encrypted message is computed using a <strike>one-time pad</strike> stream ... |
Whenever you're trying to attack a scheme that is [algebraically] relatively simple like this one, a sensible first step is to write out everything you know. Now, considering the information you've been given, try and substitute things into oneanother, and see where this leads you.
---------
Let $(m,c)$ be the fi... |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ is chosen randomly from $\mathbb Z_p-1^*$. The encrypted message is computed using a <strike>one-time pad</strike> strea... |
I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ is chosen randomly from $\mathbb Z_{p-1}^*$. The encrypted message is computed using a <strike>one-time pad</strike> str... |
Whenever you're trying to attack a scheme that is [algebraically] relatively simple like this one, a sensible first step is to write out everything you know. Now, considering the information you've been given, try and substitute things into oneanother, and see where this leads you.
---------
Let $(m,c)$ be the fi... |
The coefficients in the polynomial are elements of the field; when you expand the polynomial:
$$(x-1)(x-2)$$
where $1$ and $2$ are field elements, the normal algebraic rules apply (because those rules are based on the field properties), you get:
$$x^2 + -(1+2)x + (1\times2)$$
where the middle coefficient is... |
I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ is chosen randomly from all distinct exponents (ie $\mathbb \{0,\dots ,p-1\}$). The encrypted message is computed using ... |
1. Yes, as long as you obey all the total usage limits and choose the IV appropriately (see below).
2. Whilst IV is a general term for any initialisation vector the recent trend has been to use the term 'IV' to refer to a random vector, and "nonce" (a contraction of "**n**-umber used **once**") to refer to an input ... |
Is it possible to use Time-based One Time Password (TOTP) algorithms to generate tokens from multiple channels (where a channel is defined as a "user" using a certain shared key $K_c$ for channel $c$), and in so doing identify the channel itself from the OTP?
For example, suppose two OTP's were generated with the sa... |
Is it possible to use Time-based One Time Password (TOTP) algorithms to generate tokens from multiple channels (where a channel is defined as a "user" using a certain shared key $K_c$ for channel $c$), and in so doing identify the channel itself from the OTP?
My overall objectives are to:
1. Generate hash out... |
I am trying to figure out if we need to use single hash function across all the places in a ssh session. i.e - signature generation/verification and HMAC calculation/validation. Is it possible to use two different hash function for signature and HMAC ? I am planning to implement SHA-256 for signature generation/verific... |
Is it necessary to use single hash function for signature generation and HMAC? |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
The RSA assumption states that it is hard to find $m$, given $c = m^e \bmod{n}$, $e$, and $n$ (for appropriate choice of $n,e$).
Suppose that there exists an algorithm, $D(c,e,n)$, that finds $m$ in 1% of cases.
What could be a pseudocode of an algorithm that can use $D(\cdot,\cdot,\cdot)$ and finds $m$ easily fo... |
Who first published the interest of more than two prime factors in RSA? |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
ElGamal in private set intersection: how to handle negative numbers? |
Let $g$ be a group generator of prime order $q$. Suppose we are given two elements $g^y$ and $x_1$. Can we find out if $y=x_1+x_2$ for some $x_2$?
Thanks |
I hope you understand your question.
Your question is that given generator $g$ of a prime order $q$ group and some element $g^y$ of that group and another element $x_1 \in Z_q$ you want to check if there is such an $x_2$ or find $x_2\in Z_q$ such that $y\equiv x_1+x_2 \pmod q$? I assume that in this setting the dis... |
Working through the exercises in *Cryptography Engineering* (Schneier, Ferguson & Kohno) I have stalled on the following exercise:
> Consider a new block cipher, DES2, that consists only of two rounds of
> the DES block cipher. DES2 has the same block and key size as DES. For
> this question you should consider th... |
Working through the exercises in *Cryptography Engineering* (Schneier, Ferguson & Kohno) I have stalled on the following exercise:
> Consider a new block cipher, DES2, that consists only of two rounds of
> the DES block cipher. DES2 has the same block and key size as DES. For
> this question you should consider th... |
Working through the exercises in *Cryptography Engineering* (Schneier, Ferguson & Kohno) I have stalled on the following exercise:
> Consider a new block cipher, DES2, that consists only of two rounds of
> the DES block cipher. DES2 has the same block and key size as DES. For
> this question you should consider th... |
I am trying to figure out if we need to use single hash function across all the places in a ssh session. i.e – signature generation/verification and HMAC calculation/validation. Is it possible to use two different hash function for signature and HMAC?
I am planning to implement SHA-256 for signature generation/veri... |
Working through the exercises in *Cryptography Engineering* (Schneier, Ferguson & Kohno) I have stalled on the following exercise:
> Consider a new block cipher, DES2, that consists only of two rounds of
> the DES block cipher. DES2 has the same block and key size as DES. For
> this question you should consider th... |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed advantage in private-key operation, with little (conjectured) reduction in security for few-enough factors. The question is: who first publi... |
Your Formulas are alright, but there is some additional information from the exercise/setup:
The exercise states, that F should be considered as a blackbox (otherwise you could use the internal stages of F, as poncho already suggested). However, as I understand it you can stil evaluate F on any input of your choice.... |
I'm looking for a method for a scenario with following requirements:
At least 3 people A,B,C,... are in a Network where they can broadcast messages to everyone but not communicate with a specific person, so that they can't get answers to their broadcasts.
Every member has a public address "Apub, Bpub, .." (max ~1... |
I'm looking for a method for a scenario with following requirements:
At least 3 people (A,B,C,...) are in a Network where they can broadcast messages to everyone but not communicate with a specific person, so that they can't get answers to their broadcasts.
Every member has a public address "Apub, Bpub, .." (max ... |
First, before I answer your questions: Money rewards are not forbidden, as far as I know, but that's not how it goes here. Feel free to check out the according [question on crypto-meta](http://meta.crypto.stackexchange.com/questions/146/is-paying-or-donating-for-answers-allowed-here/).
I think, there are few concept... |
In a project of mine i took a 24-bit bitmap image and i performed lsb steganography over it (saved a black and white image inside each of the planes R, G, B) using pixel shuffling and xor encryption.
Is my stenography easy to detect? and what would it take to conceal it? |
What makes lsb stenography detectable? and what would help in concealing it? |
**Does mapping a large character-set hash onto a small character-set hash lower entropy for a fixed size substring?**
I'm writing a python app that involves generating passwords for websites. During the application I want to convert hexidecimal hashes to alphanumeric strings, and take the first twenty characters of ... |
How does converting character set affect hash entropy? |
What is the proper/canonical way to do this?
For example, $0 < r1 < 1$ and $0 < r2 < 1$. Presuming uniformly distributed probabilities for the two, combining/averaging them is going to bias very quickly towards $0.5$.
The specific use case I have is a game/simulation I'm programming. An entity has a random number... |
(I updated the title, as I think there was some confusion as to the question)
Here's the question:
For example, if I have a bit stream that is 64K bytes long and there is about 16 *8 bits worth of entropy randomly dispersed in that byte stream, so I have 16*8 bits worth of entropy.
However, if I SHA256 that b... |
Is it possible to leverage a preexisting implementation of AES-GCM to provide the key security benefits essential for full-disk encryption (similar to AES-XTS)? GCM is a popular encryption mode supported by several libraries and with fast implementations in hardware, and on its own GCM has nice properties including par... |
Is it possible to tweak AES-GCM so that it is satisfactory for whole-disk encryption (like XTS mode)? |
Multi-prime RSA is now a well known technique: use more than two distinct prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed boot in private-key operation, with little (conjectured) reduction in security for few-enough factors. Compaq was among the first to come-up... |
I'd need a crypto system allowing online yes/no votes but without revealing who voted what. Is a "partial" homomorphic crypto system what I'm after? Would, for example, Damgard-Jurik work in my case?
In my scheme there would be a server getting the votes and the server shouldn't see who voted what. However we can co... |
Homomorphic crypto allowing anonymous yes/no votes? |
Suppose your private key $d_1$ has been exposed. Instead of changing $p$ and $q$, instead you just choose a new public and private key (say $e_2$ and $d_2$) and use these instead. What kinds of attacks could someone perform knowing $N,e_1,e_2,d_1$ (where $e_1$ is the first public key)? |
Necessity of changing $p$ and $q$ when your private key is exposed? |
Multi-prime RSA is now a well known technique: it uses $k>2$ distinct secret prime factors in the public RSA modulus, with the advantage that, using the [CRT][1], we can gain a speed boost in private-key operation, with little (conjectured) reduction in security for small-enough $k$; the speedup factor relative to 2-pr... |
Sending uncompressed 24-bit bitmap images somewhat is a red flag that basic stego is in use. That would be slightly less apparent with JPEG+lossless compression, PNG, or GIF (lossy compression would destroy the hidden message given the encoding used; more sophisticated stenographic schemes survive that).
I suggest t... |
Sending uncompressed 24-bit bitmap images somewhat is a red flag that basic stego is in use. That would be slightly less apparent with JPEG (and lossless compression), PNG, or GIF (lossy compression would destroy the hidden message given the encoding used; more sophisticated stenographic schemes survive that).
I sug... |
Say following is my protocol:
Alice ------------------------> R1 Bob
Alice Pk(R1),R2 <----------------------- Bob
Alice ------------------------> Pk(R2) Bob
Alice Pk(S) <------------------------ Bob
Where Pk is pre-share... |
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