instruction stringlengths 15 30k |
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I currently try to implement Ed25519 following this [draft][1]. I have implemented every field operation except the reduction by the group order $q$ (in chapter 5). I looked for a reduction algorithm and found montgomery reduction and barrett reduction. Because Barrett reduction seems to be more fitting I tried to unde... |
I'm pretty familiar with using ssh-keygen to create groups that go in the /etc/ssh/moduli file for the Diffie-Hellman Group Exchange in openssh. Reading over the [man page][1], it says "By default, each candidate will be subjected to 100 primality tests. This may be overridden using the -a option." I'm making an educ... |
In SSL and TLS, why is there a separate Change Cipher Spec Protocol rather than
including a change_cipher_spec message in the Handshake Protocol? |
What is the advantage of AEAD ciphers? Why is the TLS working group pushing for them? I thought modern cipher suites require SHA256 for authentication. What advantage is there to including Poly1305?
Slight additional question: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 has GCM and SHA256. What is GCM used for, and what i... |
http://cr.yp.to/antiforgery/cachetiming-20050414.pdf states the following:
> So what went wrong? Answer: NIST failed to recognize that table
> lookups do not take constant time. “Table lookup: not vulnerable to
> timing attacks,” NIST stated in [19, Section 3.6.2]. NIST’s statement
> was, and is, incorrect.
Se... |
can non assembly crypto libraries truly be secure against timing attacks? |
If Alice and Bob both start with a shared OTP $P_0$, which is 256-bytes long, and Alice wants to send a 512-byte message, would it be secure to send the first 256 bytes with standard OTP (`(a+b)%256` or the like), then generate another 256 bytes of true randomness ($P_1$), run that through the OTP and send the encrypte... |
Extend OTP on random data? |
I've implemented this algorithm, which, working from the end of the message backwards, creates a valid CBC ciphertext from any plaintext, using the block cipher's decryption operation instead of the encryption operation.
[![CBC][1]][1]
I bet this is described in the literature, somewhere. Possibly as a bad idea.
... |
I would like to know if there is any research work using [CP-ABE][1] for threshold cryptography, if there is not, is it interesting to do it ?
thanks.
[1]: https://www.cs.utexas.edu/~bwaters/publications/papers/cp-abe.pdf |
> So how secure can non-assembly code truly ever be against timing attacks?
First of all, let me state that this is a tricky subject.
The simplest method is of course to do away with the lookup tables or and other components that are vulnerable to timing attacks. So when a cipher designed, it should require a min... |
> So how secure can non-assembly code truly ever be against timing attacks?
First of all, let me state that this is a tricky subject.
The simplest method is of course to do away with the lookup tables or and other components that are vulnerable to timing attacks. So when a cipher designed, it should require a min... |
In SSL and TLS, why is there a separate Change Cipher Spec Protocol rather than including a change_cipher_spec message in the Handshake Protocol? |
We recently had [the question][1] whether it's possible to have multiple private keys with one public key for the [cramer-shoup cryptosystem][2].
There [it was stated][3] that finding such "secondary" private keys is possible if $log_{g_1}(g_2) \bmod q$ is known. However computing this discrete logarithm is infeasib... |
Is Cramer-Shoup backdoorable? |
So, I was having this weird thought. If the checksums(MD5 or SHA...) are unique to any file and are modified if any part of the file is edited, why cant the checksums be decoded back to get the original file? That is if I want to send a large(say 700MB) video, instead I could send just the hash and the file be decoded ... |
Is Checksum to file back decoding possible? |
In `ssh-keygen.c` of the OpenSSH source code, there is [the following call](https://anongit.mindrot.org/openssh.git/tree/ssh-keygen.c#n2546):
if (prime_test(in, out, rounds == 0 ? 100 : rounds,
generator_wanted, checkpoint,
start_lineno, lines_to_process) != 0)
...and a [comment for th... |
I am designing a user registration protocol for a system where I control both clients and servers. The aim is to establish a symmetric key for subsequent authentication, while minimizing the work load on the server side. The security concerns are less about privacy than about integrity of the system and resistance to... |
I want to set up the following:
- An untrusted server should host user sessions and authenticate users without knowing their passwords or being capable of creating a fake user session in the user's name.
- This is accomplished by making all sessions publicly verifiable by making public the information necessary t... |
Several companies offer customized cryptographic algorithms, for example Crypto AG (http://www.crypto.ch/en/company):
> The individually created customer algorithms are unknown to anyone
> else and are not used by anyone else. A cryptographic attack is not
> possible, even from an identical unit.
Only the custo... |
Per http://crypto.stackexchange.com/questions/27282/can-non-assembly-crypto-libraries-truly-be-secure-against-timing-attacks array lookups are vulnerable to timing attacks. Like if you do `cresult[map[i]]` and `map` is an array and `cresult` is a string then `map` is vulnerable to timing attacks because it's an array b... |
can string lookups be vulnerable to timing attacks like array lookups are? |
From what I have learned about RSA encryption, the message M and the modulo n must be coprime because Euler's theorem only holds for coprime numbers? for example, what happens if I choose p = 3, q = 11, n = p*q = 33, ϕ(n) = 20, e = 7, d = 3, and I choose the message M to be 66? when I try to encrypt the message : m^e m... |
RSA Encryption: What happens if n is a factor of the message M? |
> If the checksums (MD5 or SHA...)
First things first: there is a **BIG** difference between a [***checksum** (aka “cyclic redundancy checks” like CRC32)*](https://en.wikipedia.org/wiki/Checksum) and a [***hash** (aka “cryptographically secure hash functions”* like MD5 and the SHA families)](https://en.wikipedia.org... |
> If the checksums (MD5 or SHA...)
First things first: there is a **BIG** difference between a [***checksum** (aka “cyclic redundancy checks” like CRC32)*](https://en.wikipedia.org/wiki/Checksum) and a [***hash** (aka “cryptographically secure hash functions”* like MD5 and the SHA families)](https://en.wikipedia.org... |
Several companies offer customized cryptographic algorithms, for example Crypto AG (www.crypto.ch/en/company):
> The individually created customer algorithms are unknown to anyone
> else and are not used by anyone else. A cryptographic attack is not
> possible, even from an identical unit.
Only the customers kn... |
http://cr.yp.to/antiforgery/cachetiming-20050414.pdf states the following:
> So what went wrong? Answer: NIST failed to recognize that table lookups do not take constant time. “Table lookup: not vulnerable to timing attacks,” NIST stated in [19, Section 3.6.2]. NIST’s statement was, and is, incorrect.
Sections 10... |
Can non-assembly crypto libraries truly be secure against timing attacks? |
Per [“Can non-assembly crypto libraries truly be secure against timing attacks?”](http://crypto.stackexchange.com/questions/27282/can-non-assembly-crypto-libraries-truly-be-secure-against-timing-attacks), array lookups are vulnerable to timing attacks. Like, if you do `cresult[map[i]]` and `map` is an array and `cresul... |
Can string lookups be vulnerable to timing attacks like array lookups are? |
> If the checksums (MD5 or SHA...)
First things first: there is a **BIG** difference between a *[**checksum**](https://en.wikipedia.org/wiki/Checksum) (aka “cyclic redundancy checks” like CRC32)* and a *[**hash**](https://en.wikipedia.org/wiki/Cryptographic_hash_function) (aka “cryptographically secure hash function... |
I would like to know if there is any research work using [CP-ABE][1] for threshold cryptography?
[1]: https://www.cs.utexas.edu/~bwaters/publications/papers/cp-abe.pdf |
As the other answer correctly stated, this is likely a bad idea and they are essentially selling only a perception of high security. People who don't have a cryptographic background may be mislead.
> How does this work? How can they offer a cryptographic algorithm that can be customized by non-specialist customers w... |
> In order to achieve very high security for privacy, would it be cryptographically secure to use one time pad ciphers in emails?
OTP offers perfect secrecy, so if it's feasible to use it, it is secure.
However, OTP alone offers no authentication and leaves the message malleable. If Alice sends a message `Y` to B... |
I would like to know if there is any research work using [CP-ABE][1] for threshold cryptography?
I want to know also if applying CP-ABE for threshold cryptography would overcome other techniques.
[1]: https://www.cs.utexas.edu/~bwaters/publications/papers/cp-abe.pdf |
For example, let $p = 3$ and $q= 11$, choose $e = 3$. What computation I have to apply in order to find the corresponding $d$? I know it's 7, but I want to know the exact process to be applied to find it. |
I understand how standard numeric FPE using a halved string in cycled Feistel networks is constructed and operates. I then read the paper regarding FFX encryption which should allow for any non-binary alphabet to also be used (http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/ffx/ffx-spec.pdf). However... |
[AESEngine.java][1], from BouncyCastle, uses table lookups as does [aes_x86core.c][2], in OpenSSL. But per [Cache-timing attacks on AES][3] table lookups like what OpenSSL and BouncyCastle are doing are vulnerable to timing attacks. So why would they use them?
[1]: https://github.com/bcgit/bc-java/blob/master/c... |
why do crypto libs use table lookups when they're vulnerable to timing attacks? |
Why do crypto libs use table lookups when they're vulnerable to timing attacks? |
I am referring to solution given in this [question](http://crypto.stackexchange.com/questions/26467/attack-for-rsa-1024-bit-with-low-public-exponent)
I need help to implement **Poncho** hint in [this comment](http://crypto.stackexchange.com/q/26467/555#comment61449_26478):
As the first question i have an RSA sign... |
I am referring to solution given in this [question](http://crypto.stackexchange.com/questions/26467/attack-for-rsa-1024-bit-with-low-public-exponent)
I need help to implement **Poncho** hint in [this comment](http://crypto.stackexchange.com/q/26467/555#comment61449_26478):
As the first question i have an RSA sign... |
On a device that does not have a hardware RNG, what is the best source for entropy?
Some options and pitfalls floating around:
- Use the ADC to read something analog: can become deterministic if there is access to power supply or some ADCs are just too stable even at LSB.
- Use un-init SRAM: power supply brown... |
Is there a secure source of entropy on a typical microcontroller? |
I am referring to solution given in this [question](http://crypto.stackexchange.com/questions/26467/attack-for-rsa-1024-bit-with-low-public-exponent)
I need help to implement **Poncho** hint in [this comment](http://crypto.stackexchange.com/q/26467/555#comment61449_26478):
As the first question i have an RSA sign... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs some computation and return the result back to it.
When we want to consider client $B$ is corrupted and construct a simu... |
I am referring to solution given in this [question](http://crypto.stackexchange.com/questions/26467/attack-for-rsa-1024-bit-with-low-public-exponent)
I need help to implement **Poncho** hint in [this comment](http://crypto.stackexchange.com/q/26467/555#comment61449_26478):
As the first question i have an RSA sign... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs some computation using client $A$ and client $B$ input and return the result back to client $B$.
Now we want to consider... |
I'm currently reading Menezes' "Handbook of Applied Cryptography", and in it, when describing the MDC-2 cryptographic hash function, has the following line:
> Choose the 64-bit non-secret constants $IV$, $\widehat{IV}$ (the same constants must be used for MDC verification) from a set of recommended prescribed values... |
MDC-2 recommended IV values? |
I am referring to solution given in this [question](http://crypto.stackexchange.com/questions/26467/attack-for-rsa-1024-bit-with-low-public-exponent)
I need help to implement **Poncho** hint in [this comment](http://crypto.stackexchange.com/q/26467/555#comment61449_26478):
As the first question i have an RSA sign... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs some computation using client $A$ and client $B$ input and return the result back to client $B$.
Now we want to consider... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs some computation using client $A$ and client $B$ input and return the result back to client $B$.
Now we want to consider... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs some computation using client $A$ and client $B$ input and return the result back to client $B$.
Now we want to consider... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. Te server performs some computation using client $A$ and client $B$ input and return the result back to client $B$.
Now we want to consider... |
According to [the Ed25519 paper][1], the (potentially long) input message is hashed twice (see Section 4 page 12 steps 1 and 3). [This webpage][2] has a nice diagram toward the bottom that illustrates this, and I confirmed it in the reference code on Supercop (see supercop-20141124/crypto_sign/ed25519/ref/sign.c, func... |
I am referring to solution given in this [question](http://crypto.stackexchange.com/questions/26467/attack-for-rsa-1024-bit-with-low-public-exponent)
I need help to implement **Poncho** hint in [this comment](http://crypto.stackexchange.com/q/26467/555#comment61449_26478):
As the first question i have an RSA sign... |
I need to strip off padding after decrypting AES(CBC)-encrypted data (I have control over encryption and data transmission), so have looked at adding the length of the original data to the payload being transmitted.
**Option 1:**
[ IV | Length | *Encrypt*(original data) ]
**Option 2:**
[ IV | *Encrypt*([ Lengt... |
> Is this approach (deriving a password from a signature) cryptographically sound?
Not in general. There are signature algorithms that are completely deterministic and signature algorithms that aren't. With the latter kind you would be unable to reproduce the password later.
With a deterministic algorithm, yes, t... |
First, the advice:
> What are the best-practices to store the message length / strip away padding?
1. Use standard padding, like [PKCS#7][1] padding. It handles finding the length uniquely for you.
2. Use encrypt-then-MAC to prevent padding oracle attacks.
(Or better yet, don't use CBC. Use an authenticated... |
In ε-differential privacy, what the ε refers?
Is it privacy value or the notation used.
can any one provide an example for the differential privacy?
|
Let $P$ be a prover willing to prove to a verifier $V$ that he knows a witness $w$ satisfying $(x,w) \in R$ for some relation $R$ and some common input $x$.
As found in the literature, $P$ can use a $\Sigma$-protocol for the relation $R$, defined as a 3-move protocol that satisfies the following properties:
- Co... |
Why is the definition of Special-honest verifier zero-knowledge probabilistic? |
I need to implement an authentication mechanism in an embedded environment which does not support floating point operations but has an AES accelerator module which allows for encyption/decryption operations.
Currently, I'm thinking of using the following approach:
1. Compute the ciphertext of the message using ... |
In ε-differential privacy, what does the ε refer to?
Is it privacy value or the notation used?
Can anyone provide an example of differential privacy?
|
What is ε in differential privacy? |
I need to implement an authentication mechanism in an embedded environment which does not support floating point operations but has an AES accelerator module which allows for encyption/decryption operations.
Currently, I'm thinking of using the following approach:
1. Compute the ciphertext of the message using ... |
In ε-differential privacy, `ε` represents the privacy parameter.
As an aside: you might want to try enhancing your research efforts… [related papers and publications](https://scholar.google.de/scholar?q=%22%CE%B5-differential+privacy%22+%2B+%22privacy+parameter+%CE%B5%22&btnG=&hl=en&as_sdt=0%2C5) mention this more t... |
In ε-differential privacy, **`ε` represents the privacy parameter**.
<hr>
**tip aside:**
You might want to try to enhance your research efforts because related papers and publications mention that more than frequently. In case of doubt, check the [Google scholar search results](https://scholar.google.de/schola... |
In ε-differential privacy, **`ε` represents the privacy parameter**.
<hr>
**Aside:** You might want to try to enhance your research efforts because related papers and publications mention that more than frequently. In case of doubt, check these [Google scholar search results](https://scholar.google.de/scholar?q=%... |
**TL;DR**
No, the approach is not secure. Use a standard like [CMAC](https://en.wikipedia.org/wiki/CMAC) instead.
**Long Version**
In order for a [message authentication code (MAC)](https://en.wikipedia.org/wiki/Message_authentication_code) to be secure, an adversary with oracle access to the MAC (basically th... |
In ε-differential privacy, **`ε` represents the privacy parameter**.
You might want to try to enhance your research efforts because related papers and publications mention that more than frequently.
Even websites like Wikipedia would have quickly provided you with an answer to your question. Quoting [Wikipedia ... |
In ε-differential privacy, **`ε` represents the privacy parameter**.
You might want to try to enhance your research efforts because related papers and publications mention that more than frequently.
Even websites like Wikipedia would have quickly provided you with an answer to your question. Quoting [Wikipedia ... |
It is generally assumed that asymmetric encryption schemes were invented in 1973 at GCHQ in Britain and, independently, in 1976 at the MIT.
Imagine, if the abstract idea of having a public key and a private key that can only decrypt what has been encrypted with the other, respectively, had been around forty years e... |
It is generally assumed that asymmetric encryption schemes were invented in 1973 at GCHQ in Britain and, independently, in 1976 at the MIT.
Imagine, if the abstract idea of having a public key and a private key that can only decrypt what has been encrypted with the other, respectively, had been around forty years e... |
Since this is an historical question, I am going to digress and make some historical corrections. In science, we give credit for important inventions to the people who published. If it turns out that someone else invented it earlier and didn't publish, they don't get credit. Obviously, they should be mentioned in passi... |
**TL;DR**
No, the approach is not secure. Use a standard like [CMAC](https://en.wikipedia.org/wiki/CMAC) instead.
**Long Version**
In order for a [message authentication code (MAC)](https://en.wikipedia.org/wiki/Message_authentication_code) to be secure, an adversary with oracle access to the MAC (basically th... |
I am right now taking a class named Applied Cryptography and our final project is to create a password hashing method using at least one existing algorithm and then add additional steps to make it harder to decrypt.
I am using SHA1 in a Console Application in c#.
The user input is hashed using SHA-1. For each byt... |
Perhaps someone can confirm my intuition:
A tree hash with leaves of size 1 (for example Blake2 in a tree-hash mode) would of course not be very efficient.
But it seems that it might be a suitable way (or maybe the only way?) to provide a verifier that's still useful if the underlying content is subject to inten... |
While searching for a mutual authentication protocol I often stumbled upon SKID3. However I encoutered different variations of it.
The basic structure is the following:
(1) A --> B: rA
(2) B --> A: rB || MAC(rB||rA||A)
(3) A --> B: MAC(rB||rA||B)
where A and B are the identifiers of the senders and recip... |
What is the original SKID3 protocol? |
> Is this approach (deriving a password from a signature) cryptographically sound?
Not in general. There are signature algorithms that are completely deterministic and signature algorithms that aren't. With the latter kind you would be unable to reproduce the password later.
With a deterministic algorithm, yes, t... |
I need to implement an authentication mechanism in an embedded environment which does not support floating point operations but has an AES accelerator module which allows for encyption/decryption operations.
Currently, I'm thinking of using the following approach:
1. Compute the ciphertext of the message using ... |
While searching for a mutual authentication protocol I often stumbled upon SKID3. However I encountered different variations of it.
The basic structure is the following:
(1) A --> B: rA
(2) B --> A: rB || MAC(rB||rA||A)
(3) A --> B: MAC(rB||rA||B)
where A and B are the identifiers of the senders and reci... |
> Is this approach (deriving a password from a signature) cryptographically sound?
Not in general. There are signature algorithms that are completely deterministic and signature algorithms that aren't. With the latter kind you would be unable to reproduce the password later.
With a deterministic algorithm, yes, t... |
The goal of this method is to achieve collision-resilience (resistance against collision attacks). The second hash can be viewed as $H(R || M)$ for message M and some randomness R that is unknown to an attacker. Now, even if an attacker could efficiently find collisions for $H$, he cannot use this ability to run the st... |
I'm trying to understand the UKS attack on KEA protocol.
This is described in this paper: [Security Analysis of KEA Authenticated Key Exchange Protocol][1]
So to summarize:
- KEA protocol:
[![enter image description here][2]][2]
- UKS attack on KEA:
"$\mathbb{M}$ registers a public key $g^a$ of some
... |
Imagine we have a 3-party protocol, including client $A$,client $B$ and a server. In this protocol client $B$ encrypts its input under its public key and sends it to the server. The server performs some computation using client $A$'s and client $B$'s input and returns the result back to client $B$.
Now we want to co... |
**Some background on formal key-exchange models**
The goal of a key-exchange (KE) is to establish a session key between two parties. Naively, we could say that a KE is secure if no adversary will be able to figure out the session key (in full) established between two honest parties. However, in formal security model... |
**TL;DR**
No, the approach is not secure. Use a standard like [CMAC](https://en.wikipedia.org/wiki/CMAC) instead. Or even better, check your AES accelerator module to see if it supports any [AEAD](https://en.wikipedia.org/wiki/Authenticated_encryption) modes of encryption like GCM, CCM, EAX.
**Long Version**
I... |
I am not exactly sure if this is for math stackexchange or crypto:
A TRNG outputs numbers in $[0,1]$ in a Gaussian distribution. I would like to convert them into uniform random bytes ($[0,255] $) to perform byte operations. What is s cryptographically secure method of doing this?
Here is an example distribution ... |
I am not exactly sure if this is for math stackexchange or crypto:
A TRNG outputs numbers in $[0,1]$ in a Gaussian distribution. I would like to convert them into uniform random bytes ($[0,255] $) to perform byte operations. What is s cryptographically secure method of doing this?
Here is an example distribution ... |
I am right now taking a class named Applied Cryptography and our final project is to create a password hashing method using at least one existing algorithm and then add additional steps to make it harder to decrypt.
I am using SHA1 in a Console Application in c#.
The user input is hashed using SHA-1. For each byt... |
I'm trying to understand attribute-based encryption schemes. Almost all articles describe that they are designed for cloud storage, but as I understand, almost all computing (encryption & decryption) is performed client-side and not in the cloud.
In this regard, I have a question: How are these schemes related to cl... |
Notation : $\mathbb{G}$ is an additive group and $\mathbb{G}_T$ is multiplicative group of prime order $q$.
Bilinear mapping $e: \mathbb{G} \times \mathbb{G} \rightarrow \mathbb{G}_T$ has to satisfy two properties.
1) $e(aP,bQ) = e(P,Q)^{ab}$ for all $P,Q \in \mathbb{G} , a,b \in \mathbb{Z}_q$
2) $e... |
As Thomas pointed out in his comment, in WPA-PSK the parties already have a shared secret (the pre-shared key), so there is no need to go through the step of Diffie-Hellman key-exchange -- *unless you want perfect forward secrecy (PFS)* (see update below).
In WPA, the client and the access point goes through a step... |
As Thomas pointed out in his comment, in WPA-PSK the parties already have a shared secret (the pre-shared key), so there is no need to go through the step of Diffie-Hellman key-exchange -- *unless you want perfect forward secrecy (PFS)* (see update below).
In WPA, the client and the access point goes through a step... |
As Thomas pointed out in his comment, in WPA-PSK the parties already have a shared secret (the pre-shared key), so there is no need to go through the step of Diffie-Hellman key-exchange -- *unless you want perfect forward secrecy (PFS)* (see update below).
In WPA, the client and the access point goes through a step... |
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