instruction stringlengths 15 30k |
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Online attacks involve an online entity - an entity that is available in real time to be used by an attacker. So if you attack a network service then you perform an online attack. Offline attacks are attacks that can be performed without such an entity, e.g. when an attacker has access to an encrypted file.
Online e... |
I have elliptic curve of equation $y^2 \equiv x^3 -x $. And the coordinate of points $Q$ and $P$. I want to solve $Q=[k]P$ (where $k$ is the unknown) by testing all possible $k$.
Is this the right approach to solve this problem?
Edit
----
I understand from comments that this is known as **Elliptic curve discret... |
**Yes! (restrictions apply)**. ISO/IEC 9796-2 (scheme 1, SHA-1 hash, option 1 also known as implicit hash identifier, alternative signature production function) is a fully standard signature scheme, based on RSA, widely used in the Smart Card industry for public key certificates and message authentication, that _adds_ ... |
What are some cryptographics hashes that do not exhibit the avalanche effect? |
What are some hashes that do not exhibit the avalanche effect? |
1. Ask yourself **if you even can** securely store the user's data.<br>
This includes to check that the user won't get sniffed by the root / admin
user.<br>Also make sure that your implementation is secure.<br>Employ
standard code review mechanisms, make sure that your implementation has
countermeasures against... |
My idea was, given that a computer could produce some sort of lookup tables on paper, could then a human use those lookup tables to create a system for digital signatures?
This was really an idea for fictional writing. I was trying to figure out whether it could be possible in a society at sort of 1950s technology t... |
Are digital signatures using preprocessed paper pads possible? |
1. Ask yourself **if you even can** securely store the user's data.<br>
This includes to check that the user won't get sniffed by the root / admin
user.<br>Also make sure that your implementation is secure.<br>Employ
standard code review mechanisms, make sure that your implementation has
countermeasures against... |
**No.**
<br>This isn't secure by itself against chosen-plaintext attacks.
This mode is known as plaintext-feedback mode (PFB) and referenced for example in [here][1].<br>
The next point is this mode hasn't received much attention in the cryptographic literature, whereas other modes (CFB, OFB, CBC, CTR) have.
T... |
**Is there research on a hash function or a MAC that can be executed without computers?**
I know there's a lot of history on hand-based ciphers and the OTP can easily be excecuted by hand. (By using numbers / letters) But modern cryptography requires authentication as well as encryption.
Now I'm asking myself, is... |
Do hand-based hash functions / MACs exist? |
**How do I safely encrypt a file?**
or formulated differentely:
**How do I safely store the data of my application in a file?**
Note: Using established tools isn't an option for this. The tasks need to be done at program level (using libraries and such). |
Any thoughts on how this can be done?
![Challenging question][1]
[1]: https://i.stack.imgur.com/smIy3.png |
Any thoughts on how this can be done? |
In ECDH protocol is possible, naturally, to use the same algorithm for calculate a secret key for both communication parties (Alice and Bob for example). It is possible to design also a same algorithm for the parties comunication in the RSA-DH protocol? |
Z=(N-XY)^2 is a surface with absolute minima (0s) anywere Y=N/X.
I know this question is naiive, but shouldn't it be possible to apply a [lossy compression][1] filter to this function which preserves values only at discrete boundaries and then search for absolute minima?
If the answer is no, is there any online r... |
Can spatial filters be used to factor composite numbers? |
$Z=(N-XY)^2$ is a surface with absolute minima ($0s$) anywere $Y=N/X$.
I know this question is naiive, but shouldn't it be possible to apply a [lossy compression][1] filter to this function which preserves values only at discrete boundaries and then search for absolute minima?
If the answer is no, is there any on... |
Any thoughts on how this can be done?
![Challenging question][1]
[1]: https://i.stack.imgur.com/smIy3.png |
Any thoughts on how this can be done? ![enter image description here][1]
[1]: https://i.stack.imgur.com/smIy2.png |
Any thoughts on how this can be done?
![Challenging question][1]
[1]: https://i.stack.imgur.com/smIy3.png |
Any thoughts on how this can be done? |
It is well-known that the Grover's algorithm reduces cryptographic strength of symmetric ciphers to a square-root - e.g. AES-256 becomes only 2<sup>128</sup> strong.
However, these statements are always made about the raw block ciphers. How about GCM-AES256, CCM-AES256 and the like? The MAC tag in GCM is at most 128... |
I asked [this question][1] recently but I was told it is not save to simply send over the identifier for your crypto method you want to use. for example, say the server has crypto method 3 5 and 6, the client had 2, 3, and 6.
The clients sends the methods it can do and the server checks the highest possible version.... |
I have this problem:
"Let *Enk<sub>k</sub>(m)* a safe block encrypting system. We define a hash function as this: <br />
i. *m* will be concatenated with *0* until *|m| = a multiple of len(block)*;<br />
ii. we broke the sequence in *n* blocks like *m<sub>... |
I asked [this question][1] recently but I was told it is not save to simply send over the identifier for your crypto method you want to use. for example, say the server has crypto method 3 5 and 6, the client had 2, 3, and 6.
The clients sends the methods it can do and the server checks the highest possible version.... |
> How does TLS ensure the use of the best crypto method both the server and client share?
It does not. The server is responsible for selecting the cipher and there is no guarantee that it will select the best. But, if a man-in-the-middle tampers with the ClientHello to change the ciphers offered to the server, then ... |
Any thoughts on how this can be done?
![Challenging question][1]
[1]: https://i.stack.imgur.com/smIy3.png |
Any thoughts on how this can be done?
> Let $\Pi_1 = (\mathrm{Gen}_1, \mathrm{Enc}_1, \mathrm{Dec}_1)$ and $\Pi_2 = (\mathrm{Gen}_2, \mathrm{Enc}_2, \mathrm{Dec}_2)$ be two encryption schemes for which it is known that at least one is CPA-secure. The problem is that you don't know which one is CPA-secure and whic... |
Any thoughts on how this can be done?
> Let $\Pi_1 = (\mathrm{Gen}_1, \mathrm{Enc}_1, \mathrm{Dec}_1)$ and $\Pi_2 = (\mathrm{Gen}_2, \mathrm{Enc}_2, \mathrm{Dec}_2)$ be two encryption schemes for which it is known that at least one is CPA-secure. The problem is that you don't know which one is CPA-secure and whic... |
I want to implement a secure chat on mobile. I like to know if the following protocol for key agreement that use any asymetric encryption exist:
Suppose Alice and Bob are two clients of the app. For this they have to register their public keys in a server, i.e,:
1) Alice generates its public and private keys (pub_A... |
Exist this chat protocol? |
If you got $n$ blocks, then you compute the encryption of each block, and let's look at one bit at position $j$. Let's call this $c_{i,j}= E(m_i)[j]$.
Now what you will get at position $i$ in your output is $(((c_{i,1} \bar{\vee} c_{i,2}) \bar{\vee}c_{i,3}) \bar{\vee} \dots )\bar{\vee}c_{i,n}$.
If we assume that ... |
I'm aware that [MD5 is broken](https://en.wikipedia.org/wiki/MD5#Security), and collisions have been found for it. I'm interested in other hashes (SHA-1, SHA-2, SHA-3) when truncated to the same digest size, i.e. 128 bits.
The time complexity of a collision attack is `2^(n/2)` (the "birthday attack"). So in the case... |
Has a collision ever been found for SHA-1/2/3 when truncated to 128 bits? |
I'm aware that [MD5 is broken](https://en.wikipedia.org/wiki/MD5#Security), and collisions have been found for it. I'm interested in other hashes (SHA-1, SHA-2, SHA-3) when truncated to the same digest size, i.e. 128 bits.
The time complexity of a collision attack is `2^(n/2)` (the "birthday attack"). So in the case... |
It is well-known that the Grover's algorithm reduces cryptographic strength of symmetric ciphers to a square-root - e.g. AES-256 becomes only 2<sup>128</sup> strong.
However, these statements are always made about the raw block ciphers. How about GCM-AES256, CCM-AES256 and the like? The MAC tag in GCM is at most 128... |
I have this problem:
> "Let ${\rm Enc}_k(m)$ a safe block encryption system. We define a hash function $H(m)$ as follows:
> 1. $m$ will be concatenated with $0$ until $|m|$ is a multiple of len(block);
> 2. we break the sequence $m$ into $n$ blocks like $m = m_0 \mathop\| m_1 \mathop\| m_2 \mathop\| \dots \matho... |
Is the hash function defined in this exercise collision-resistant? |
Any thoughts on how this can be done?
> Let $\Pi_1 = (\mathrm{Gen}_1, \mathrm{Enc}_1, \mathrm{Dec}_1)$ and $\Pi_2 = (\mathrm{Gen}_2, \mathrm{Enc}_2, \mathrm{Dec}_2)$ be two encryption schemes for which it is known that at least one is CPA-secure. The problem is that you don't know which one is CPA-secure and whic... |
There are three ways in encrypting and signing a message:
1. Send Enc(msg, Sig(msg))
2. Send Enc(msg) and Sig(msg)
3. Let E = Enc(msg). Send E and Sig(E)
Are all of these methods equivalently secure, ensuring no one will be able to read my message, and no one will be able to tamper my message? |
I know that the industrial standard is normally sending data in the following format:
Send Encr(msg, Sign(msg))
Is the following way a secure as well?
Send Enc(msg) and Sig(msg)
By secure, I mean no one will be able to read my message, and no one will be able to tamper my message. |
Is sending encrypted message and signed message a secure way of transmitting data? |
[Wikipedia claims](https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a 0, then encrypting a 1, then... |
How can a block cipher in counter mode be a reasonable PRNG when it's a PRP? |
> `This [Carter-Wegman] MAC is not, in general, secure in the quantum setting`
This is true; however we need to ask "what is this setting, and is it a realistic one?"
This setting is one where the adversary can ask queries that are composed of a superposition of quantum states, and the oracle returns the superpos... |
> `This [Carter-Wegman] MAC is not, in general, secure in the quantum setting`
This is true; however we need to ask "what is this setting, and is it a realistic one?"
This setting is one where the adversary can ask queries that are composed of a superposition of quantum states, and the oracle returns the superpos... |
[Wikipedia claims](https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a 0, then encrypting a 1, then... |
[Wikipedia claims](https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a 0, then encrypting a 1, then... |
> `This [Carter-Wegman] MAC is not, in general, secure in the quantum setting`
This is true; however we need to ask "what is this setting, and is it a realistic one?"
This setting is one where the adversary can ask queries that are composed of a superposition of quantum states, and the oracle returns the superpos... |
For a random function you'd expect all outputs to be different unless you generate about $2^{n/2}$ blocks ([birthday problem](https://en.wikipedia.org/wiki/Birthday_problem)). Thus PRPs and PRFs are indistinguishable if you generate significantly fewer than $2^{n/2}$ blocks.
For a 128 bit cipher this is *a lot* of d... |
For a random function you'd expect all outputs to be different if you generate fewer than $2^{n/2}$ blocks ([birthday problem](https://en.wikipedia.org/wiki/Birthday_problem)). Thus PRPs and PRFs are indistinguishable unless you observe about $2^{n/2}$, at which point you'd expect collisions using the PRF but not using... |
For a random function you'd expect all outputs to be different if you generate fewer than $2^{n/2}$ blocks ([birthday problem](https://en.wikipedia.org/wiki/Birthday_problem)). Thus PRPs and PRFs are indistinguishable unless you observe about $2^{n/2}$, at which point you'd expect collisions using the PRF but not using... |
[Wikipedia claims](https://en.wikipedia.org/w/index.php?title=Cryptographically_secure_pseudorandom_number_generator&oldid=656404160#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a... |
For a random function you'd expect all outputs to be different if you generate fewer than $2^{n/2}$ blocks ([birthday problem](https://en.wikipedia.org/wiki/Birthday_problem)). Thus PRPs and PRFs are indistinguishable unless you observe about $2^{n/2}$, at which point you'd expect collisions using the PRF but not using... |
[Wikipedia claims](https://en.wikipedia.org/w/index.php?title=Cryptographically_secure_pseudorandom_number_generator&oldid=656404160#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a... |
[Wikipedia claims](https://en.wikipedia.org/w/index.php?title=Cryptographically_secure_pseudorandom_number_generator&oldid=656404160#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a... |
[Wikipedia claims](https://en.wikipedia.org/w/index.php?title=Cryptographically_secure_pseudorandom_number_generator&oldid=656404160#Designs_based_on_cryptographic_primitives):
> A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a... |
A [comment](http://crypto.stackexchange.com/questions/2199/how-to-authenticate-over-open-channel#comment3538_2199) on [another question](http://crypto.stackexchange.com/questions/2199/how-to-authenticate-over-open-channel) made me wonder about something:
> Assume you're on a rather constrained platform — say, ... |
I have read that the rsa numeric signature works as the following:
1. Generation of keys : p,q,N,e,d
2. Process of signing the message m (which is BigInteger) : it uses the secret key sk=(p,q,d) so that s=(m^d)mod(N) where N=p*q.
Why do we use the secret key to sign the message?
How I can hash the message ?
... |
I have read that the RSA numeric signature works as the following:
1. Generation of keys : $p,q,N,e,d$
2. Process of signing the message $m$ (which is BigInteger) : it uses the secret key $sk=(p,q,d)$ so that $s=m^d\bmod N$ where $N=p*q$.<br>
Why do we use the secret key to sign the message?<br>
How I can hash ... |
**Is there research on a hash function or a MAC that can be executed without computers?**
I know there's a lot of history on hand-based ciphers and the OTP can easily be excecuted by hand. (By using numbers / letters) But modern cryptography requires authentication as well as encryption.
Now I'm asking myself, is... |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search on the serial number shows only my word... |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search using the serial number as a keyword sh... |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search using the serial number as a keyword sh... |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search using the serial number as a keyword sh... |
How do we know one-way functions can be iterated? |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search using the serial number as a keyword sh... |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search using the serial number as a keyword sh... |
I was looking at the serial numbers of the certificates for www.google.com and wordpress.com. Wordpress was listed by openssl as:
04:0B:D4:F8:25:88:C5
This serial is listed as the serial for both my specific wordpress.com domain and for www.wordpress.com. A google search using the serial number as a keyword sh... |
How I can create the homomorphic multiplication in Elgamal, using only 2 cipher texts c1 and c2 and a public key ?? Do I need to know the messages m1 and m2 ?? |
$Z=(N-XY)^2$ is a surface with absolute minima ($0s$) anywere $Y=N/X$.
I know this question is naiive, but shouldn't it be possible to apply a [lossy compression][1] filter to this function which preserves values only at discrete boundaries and then search for absolute minima?
If the answer is no, is there any on... |
How can we delete this question? I dont want it. |
How can we delete this question? |
Any thoughts on how this can be done?
> Let $\Pi_1 = (\mathrm{Gen}_1, \mathrm{Enc}_1, \mathrm{Dec}_1)$ and $\Pi_2 = (\mathrm{Gen}_2, \mathrm{Enc}_2, \mathrm{Dec}_2)$ be two encryption schemes for which it is known that at least one is CPA-secure. The problem is that you don't know which one is CPA-secure and whic... |
How can we delete this question? I dont want it. |
How can we delete this question? |
I'm going to agree with [@fgrieu][1]'s marvelous post above in a back-handed way.
My answer is: **No**, you don't *have* to use an *HMAC*. Do it anyway.
As you noted, some hashes, sush as *SHA-3* (especially in its *Keccak* form), *Skein* (which I was a team member on), and others will work just fine. In the case... |
Any thoughts on how this can be done?
> Let $\Pi_1 = (\mathrm{Gen}_1, \mathrm{Enc}_1, \mathrm{Dec}_1)$ and $\Pi_2 = (\mathrm{Gen}_2, \mathrm{Enc}_2, \mathrm{Dec}_2)$ be two encryption schemes for which it is known that at least one is CPA-secure. The problem is that you don't know which one is CPA-secure and whic... |
How can I compute homomorphic multiplication in ElGamal? That is: Given two ciphertexts $(R_1,c_1)$ and $(R_2,c_2)$ corresponding to plaintexts $m_1$ and $m_2$ under some public key; how can I compute a ciphertext $(R,c)$ that is an encryption of $m_1\cdot m_2$ under that same public key? |
How to perform homomorphic multiplication in ElGamal? |
Can i get a list of over hard and long RSA keys? i think i have found a vulnerability in RSA Algorithm |
$Z=(N-XY)^2$ is a surface with absolute minima ($0s$) anywere $Y=N/X$.
I know this question is naiive, but shouldn't it be possible to apply a [lossy compression][1] filter to this function which preserves values only at discrete boundaries and then search for absolute minima?
If the answer is no, is there any on... |
[Bruce Schneier](https://www.schneier.com/blog/archives/2013/09/the_nsa_is_brea.html#c1675929) and [Gregory Maxwell](https://lists.torproject.org/pipermail/tor-talk/2013-September/029956.html) have both stated that they believe the constants chosen for NIST's P curves (i.e. P-256r) are cooked. DJB has put together a [d... |
Could anyone, please, tell me history of birth of Blowfish algorithm? Specifically, what is substantiation of Blowfish key length to be in range from 32 till 448 bits? Why, for example, it wasn't 64-512 so it's minimal key could be 2 times shorter than AES and maximal key could be exactly 4 times taller than AES with 2... |
Introduction
---
BCrypt is a password-based [KDF][1] (far from state-of-the-art, but better than PBKDF2, because BCrypt requires sizable RAM, which greatly increases the cost of hardware-accelerated password search).
Bcrypt is based on the blockcipher Blowfish, with the initial processing of the password _reminisc... |
I have client connecting a server over https to send and retrieve data.
* The client always connects via https
* The certificate is known to the client beforehand (hard coded into the software)
* The passwort is auto-generated, so not choosen by the client
For authentication, is there any reason I should do any... |
Say I’m using a 128 bit block cipher and would like to encrypt a 256 bit input that would be divided to two blocks, however I wish that every bit changed in the ciphertext would completely corrupt both plaintext blocks when decrypted.
Consider the following simple solution:
**Encryption:**
1. XOR the first pla... |
Would this method deliver a perfectly non-malleable encryption for at least two blocks? |
Say I’m using a 128 bit block cipher and would like to encrypt a 256 bit input that would be divided to two blocks, however I wish that every bit changed in the ciphertext would completely corrupt both plaintext blocks when decrypted.
Consider the following simple solution:
**Encryption:**
1. XOR the first pla... |
Say I’m using a 128 bit block cipher and would like to encrypt a 256 bit input that would be divided to two blocks, however I wish that every bit changed in the ciphertext would completely corrupt both plaintext blocks when decrypted.
Consider the following simple solution:
**Encryption:**
1. XOR the first pla... |
> Will this method deliver true non-malleability?
No. If we set the ciphertext to the value $(B, B)$, then the decrypted plaintext will have the second block as $B$ (assuming that the PCBC mode uses an implicit plaintext/ciphertext IV of 0; if it's two known constants, it's easy to adjust for that).
|
> Will this method deliver true non-malleability?
No. If we set the ciphertext to the value $(B, B)$, then the decrypted plaintext will have the second block as $B$ (assuming that the PCBC mode uses an implicit plaintext/ciphertext IV of 0; if it's two known constants, it's easy to adjust for that).
Even if we i... |
Say I’m using a 128 bit block cipher and would like to encrypt a 256 bit input that would be divided to two blocks, however I wish that every bit changed in the ciphertext would completely corrupt both plaintext blocks when decrypted.
Consider the following simple solution:
**First version** (*note there is a ref... |
Say I’m using a 128 bit block cipher and would like to encrypt a 256 bit input that would be divided to two blocks, however I wish that every bit changed in the ciphertext would completely corrupt both plaintext blocks when decrypted.
Consider the following simple solution:
**First version** (*note there is a ref... |
Is it possible (and is there any research I can read) to have 2 key pairs for different ciphers, for example RSA 1024 and some yet to be released EC (or other asymmetric cipher) than uses 1024 bit keys, that have the same public key? |
Is it possible to have colliding public keys across ciphers? |
$Z=(N-XY)^2$ is a surface with absolute minima ($0s$) anywere $Y=N/X$.
I know this question is naiive, but shouldn't it be possible to apply a [lossy compression][1] filter to this function which preserves values only at discrete boundaries and then search for absolute minima?
If the answer is no, is there any on... |
Say I’m using a 128 bit block cipher and would like to encrypt a 256 bit input that would be divided to two blocks, however I wish that every bit changed in the ciphertext would completely corrupt both plaintext blocks when decrypted.
Consider the following simple solution:
**First version** (*note there is a ref... |
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