instruction stringlengths 15 30k |
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Is FIPS 140-2's "Continuous random number generator test" practical? |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where $\: B = \text{"A... |
From the original BEAST paper, it seems to me that you need the same session key when encrypting data, so you can check if the original plaintext block is the same as your chosen plaintext (which is impossible with different keys). However, in modes with PFS, the keys are different in each session, so doesn't this foil... |
Are SSL modes with forward secrecy vulnerable to the BEAST attack? |
I am only a beginner and doesn't know much about https. I have heard that they uses somekind of a key and is shared between them. If an attacker wishes to attack could he be able to capturebthe key and attack? |
how does https key get shared? |
I am assuming there is a very simple way of working this out by brute force, but I am not sure if there is a better way.
I have a file of data that I wish to get (my data, generated by a machine). This file is encrypted by some method that I have no details of (and the company has folded).
However, as well as the e... |
No, an attacker listening to the SSL connection is unable to get a copy of the keys.
This is actually a fairly fundamental property of SSL (or any other protocol that encrypts traffic); we're encrypting the traffic because someone might be listening in, and we want to prevent them from being able to understand the t... |
Is it possible for myself to change the key size (say from 2048 to 4096) on an EXISTING PGP / GPG key, and just republishing that key?
Or do I have to generate a new key all together?
I want to say that you have to create a new key pair, but I don't have enough documentation either way to support a claim. |
Is it possible to change PGP / GPG Key Size on an exisiting key? |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}\hspace{-0.02 in}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where... |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}\hspace{-0.02 in}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where... |
[In the section 3 (pag 44)][1] say: "Then each one-time signature key must be generated twice, once for the MSS public key generation and once during the signing phase". Also defined PRNG: Seed_{in} \rightarrow (RAND, SEED_{out}), where RAND is a random number. Finally, described a example of MSS + W-OTS, here SeedOTS_... |
[In the section 3 (pag 44)][1] say: "Then each one-time signature key must be generated twice, once for the MSS public key generation and once during the signing phase". Also defined $\text{PRNG}$: $\text{Seed}_{\text{in}} \rightarrow (RAND, SEED_{\text{out}})$, where $\text{RAND}$ is a random number. Finally, describe... |
[This paper on semi-generic algorithms](http://www.iacr.org/archive/asiacrypt2010/6477543/6477543.pdf) considers
<br>
["non-standard properties of the employed hash function"](http://www.iacr.org/archive/asiacrypt2010/6477543/6477543.pdf#page=15).
<br>
For [BLS signatures](http://en.wikipedia.org/wiki/BLS_%28crypto... |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}\hspace{-0.02 in}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where... |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}\hspace{-0.02 in}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where... |
A Gap-CDH group is such that, given group elements $g, a = g^x, b = g^y$, it is hard to compute $g^{xy}$, but, given a group element $c$, easy to verify if $c = g^{xy}$. While such groups have been proposed, and it is obviously feasible to define a group where Decision Diffie-Hellman is demonstratively easy, exactly wh... |
Do Gap-CDH groups exist? |
I have to deside, whether a document, which I am given, was correctly signed by a private key.
my Ideas is to sign the document id using RSA with the private key and to print the following onto the document:
encrypt(privateKey, id)
id
- Which requirenments should be fullfilled by the id, for the `enc... |
How to safely sign a 6 characters String? |
Let's say that we have a key exchange of some sort, which leaves A and B sharing the long-term secret $S$.
A and B then wants to use AES-CTR for the communication, which leaves us with several possible strategies:
1. During the key exchange, A and B both generate and send nonces $N_a$ and $N_b$ which are mixed in... |
A Gap-CDH group is such that, given group elements $g, a = g^x, b = g^y$, it is hard to compute $g^{xy}$, but, given a group element $c$, easy to verify if $c = g^{xy}$. While such groups have been proposed, and it is obviously feasible to define a group where Decision Diffie-Hellman is demonstratively easy, exactly wh... |
If I am not mistaken, plaintext RSA is not secure. So, I have read that padding and hashing is needed to make the RSA algorithm secure. However, I am confused on what does padding or armoring mean in this context. What does RSA-padding mean, how does it work?
For instance [here][1] I have read about this, but I do n... |
RSA padding: what is it and how does that work? |
I'd like to refer you to the [other answer](http://crypto.stackexchange.com/a/9042/5231) in the original question. Suppose your laptop and Snowden's laptop are both capable of quantum communication. Suppose there is also a quantum phone book, or a quantum DNS service. When his passport got revoked, Snowden's address is... |
The usual case to distinguich a pseudorandom function from a random function is to assume that the adversary can choose the plaintext blocks. Is there another case (game) in which the adversary can not choose the plaintext blocks ?
Thank you. |
I am new to this cryptography and in the source from which i study it is said that if we know the first few bits of a pseudo random sequence we can predict the whole of it.How is it possible? |
Why is it said that if we know few bits of pseudo random sequence we can predict the whole of it? |
I am new to this cryptography and in the source from which i study it is said that if we know the first few bits of a pseudo random sequence we can predict the whole of it.How is it possible?
The source:https://class.coursera.org/crypto-007/lecture/5
move to 7min 40sec and this is the source. |
The other answers cover it quite elaborately, but in short: No.
But let's consider this to be a game, with the following assumptions:
- There is a person called "Snowden". Somewhere. In the world. And he has no way to authenticate himself.
- Snowden initially trusts no one.
- There is no trustworthy way to a... |
I am new to this cryptography and in the source from which i study it is said that if we know the first few bits of a pseudo random sequence we can predict the whole of it.How is it possible?
The source:http://www.youtube.com/watch?v=NjedHm04ETM
move to 7min 40sec and this is the source. |
[In the section 2 (end of pag 42)][1] say: "Then he generates the one-time signature $\sigma_{\text{OTS}}$ of the digest using the $s$-th one time signature key". My question: Is choose $s$ in random form? Is possible to exist $s$ collisions to the signature process?
best regards
[1]: http://www.e-reading-lib... |
As expressed, this is not possible. A zero-knowledge proof cannot be non-interactive. The reason is that any non-interactive proof can be forwarded to a third party who will accept it. This is excluded by standard definitions of zero-knowledge.
Could you rephrase you question and explain more precisely what you expe... |
(Already asked the same question on stackoverflow but I was told to better ask here.
http://stackoverflow.com/questions/17527192/one-time-pad-with-dh-and-cryptographic-hash-function)
I know: Never do your own crypto.
But this question is just theoretical.
Assume you do a Diffie-Hellmann Key Exchange with a se... |
One Time Pad with DH and Cryptographic Hash Function? |
As expressed, this is not possible. A zero-knowledge proof cannot be non-interactive. The reason is that any non-interactive proof can be forwarded to a third party who will accept it. This is excluded by standard definitions of zero-knowledge.
Could you rephrase you question and explain more precisely what you expe... |
Could anyone tell me what the difference is between a THEORETICAL ATTACK (Like the one done on SHA-1) and an actual attack (Like the one done on SHA-0). Is a theoretical attack a proposed method of attacking, that no one's ever done due to lack of resources (like computing power)?
Thanks in-advance,
Tom |
(Already asked the same question on stackoverflow but I was told to better ask here.
http://stackoverflow.com/questions/17527192/one-time-pad-with-dh-and-cryptographic-hash-function)
I know: Never do your own crypto.
But this question is just theoretical.
Assume you do a Diffie-Hellman Key Exchange with a ser... |
Stream cipher with Diffie-Hellman and Cryptographic Hash Function? |
What would be a good analogue with which to describe Message Authentication Codes to a person who has little to no understanding of cryptography?
For instance, a vault is a reasonable analogue for symmetric authenticated encryption: anyone with the key can open the vault and inspect, alter, or replace the contents. ... |
For testing purpose, I want to create a PKCS#12 file in which the private key doesn't match the certificate. Is there any tool which will help me do this?
If I use "openssl pkcs12 -export" command line to create the p12 file using a cert and a private key which are mismatched, then openssl gives me an error
... |
For testing purpose, I want to create a PKCS#12 file in which the private key doesn't match the certificate. Is there any tool which will help me do this?
If I use `openssl pkcs12 -export` command line to create the `p12` file using a cert and a private key which are mismatched, then `openssl` gives me an error
... |
[In the section 2 (end of page 42)][1] say:
> Then he generates the one-time signature $\sigma_{\text{OTS}}$ of the digest using the $s$-th one-time signature key $X_s$, $s\in\{0,\dots,2^H-1\}$.
My question: Is $s$ chosen in random form? Is it possible to have $s$ collisions to the signature process?
[1]... |
Am I thinking about this correctly?
Consider that the keyspace of the Playfair cipher is equivalent to all permutations of the alphabet, e.g. the number of distinct permutations of 25 objects, and is equal to 1.551 x 10^25. (A lot!)
1. What is the keyspace of Four-Square, when considering both keys, as presented ... |
I'm using AES to encrypt the message.
both sender and receiver know the passphrase, but only sender knows IV
I assume that receiver needs to know IV to decypher text;
is it safe to pass IV along with the cyphertext over an unsecured network, or will this compromise the security?
I'm using https://code.google.... |
I'm using AES to encrypt the message.
both sender and receiver know the passphrase, but only sender knows IV and salt
I assume that receiver also needs to know IV and salt to decypher text;
is it safe to pass IV and salt along with the cyphertext over an unsecured network, or will this compromise the security?
... |
Am I thinking about this correctly?
> Consider that the keyspace of the Playfair cipher is equivalent to all permutations of the alphabet, e.g. the number of distinct permutations of 25 objects, and is equal to $1.551 · 10^{25}$. (A lot!)
> 1) What is the keyspace of Four-Square, when considering both keys, as pr... |
How would one go about selecting an appropriate bijective function for introducing permutations into a cipher or hash?
For example, $f(x) = x+1 \space mod \space n$ is a bijective function, but isn't particularly good as a permutation, in that the outputs do not vary sufficiently when an input bit is changed.
The... |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}\hspace{-0.02 in}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where... |
The SIGMA paper does not describe how a "response message" for SIGMA-I would be implemented.
<br>
If it was implemented as, for example, $B$ sending $\:\operatorname{MAC}_{K_m}\hspace{-0.02 in}(\text{"ACK"})\:$ to $A$, then that would
<br>
not actually provide the desired _peer awareness_ property in the case where... |
It depends. There is no single answer, and no single recipe that works for all block ciphers. The permutation is chosen to work well with the rest of the block cipher design. Therefore, this question can't be answered in general. A question like "Why did cipher X use Y as its permutation?" would be more meaningful... |
The HE that supports any function on ciphertexts is known as Fully Homomorphic Encryption (FHE), The Partially Homomorphic Encryption (PHE) includes encryption schemes that have homomorphic properties, with respect to one operation.
Symmetric homomorphic encryption schemes( Domingo Ferrer, Castellucia, etc.) are als... |
I would like to encrypt a String asymmetric.
I would like the cryptogramm to be as short as as plaintext. (or shorter)
I've red about the format preserving encryption functions - are there asymmetric variants of them? |
Asymmetric format preserving encryption? |
Well, yes, there is a probabilistic polynomial time algorithm the determines whether a number is a Carmichael number of not (probabilistic in the sense that it always returns the correct value, it terminates quickly with high probability). However, it isn't as helpful as you are thinking for your application.
The ... |
I know that Homomorphic Encryption (HE) which supports any function on ciphertexts is known as Fully Homomorphic Encryption (FHE), and I know that the Partially Homomorphic Encryption (PHE) includes encryption schemes that have homomorphic properties, with respect to one operation.
Are “Symmetric homomorphic encrypt... |
Homomorphic Encryption (HE) which supports any function on ciphertexts is known as Fully Homomorphic Encryption (FHE), while Partially Homomorphic Encryption (PHE) includes encryption schemes that have homomorphic properties, with respect to one operation (e.g., only addition or only multiplication, but not both).
A... |
In [point 4 of the Algorithm 4.2 (Classic Merkle Tree Traversal)][1] say Stack_h.update(2) (Each stack receives two updates). I am trying understand "two updates" but I cann't get. There is an example in the page 19 from [this thesis][2]. Here only update one time. For example in the step 1 Why update stack one time? ... |
[D-wave systems][1] has released a commercially viable quantum computer. This means; in theory, that all asymmetric encryption algorithms, such as RSA are now useless, due to the speed at which quantum computers can factor.
Has RSA been cracked yet? If not; why hasn't it?
The reason for our company's concern i... |
I would like to know which area of Mathematics would be most beneficial to cryptography. Surely Algebraic Number Theory and maybe to a lesser extend, Elliptic Curves, are closely linked to Cryptography; but are there more fields that would apply neatly to Cryptography?
What topics would you recommend to a Maths grad... |
Which area of Maths should I pursue? |
I would like to encrypt a string asymmetrically.
<br>
I would like the ciphertext to be as short as as plaintext. (or shorter)
I've read about format preserving encryption functions - are there asymmetric variants of them? |
This seems to me a situation of the tail wagging the dog. Personally I have always found something I want to do such as zero knowledge proofs, faster primality testing, shorter signatures and then learned the relevant maths - bilinear pairings, elementary number theory and elliptic curves respectively.
Cryptography is... |
I am a bit confused about the use of IV , and key hash .
is the key hash and IV stored inside the headers of the cipher text? why is that?
isnt it a security risk to store this header information?
Thanks |
From reading [RFC 2015](https://www.ietf.org/rfc/rfc2015.txt) (MIME security with PGP), and from looking at the raw format of (GnuPG) encrypted and digitally signed email messages, it seems that first a signature is calculated from the plain text message, and then both are encrypted.
My question is why isn't this v... |
Is OpenPGP vulnerable to the "crypto doom principle"? |
We use MobilePASS at work but the latest version of the android client seems to be buggy so I wanted to have a go at implementing the algorithm myself.
It looks to be based on the HMAC-SHA256 OTP algorithm. The client provides the user with the secret key when creating a new token which is copied into a web interfac... |
How does SafeNet MobilePASS generate passwords? |
Your next step should be to try all of the standard techniques for breaking [substitution ciphers](https://en.wikipedia.org/wiki/Substitution_cipher) or ECB mode. You basically have a substitution cipher, where the alphabet is a 64-bit block (each 64-bit block plays the role of a single "letter"/"character"). Another... |
I'm looking at a datagram-based protocol that encrypts a payload. The payload is encrypted with AES or blowfish in CBC mode, and the result is then authenticated with a HMAC.
To save space, the protocol uses a zero IV, but prepends a special prefix to the data before encryption.
The prefix consists of 12 random b... |
CBC with random prefix but no IV - secure? |
I am a bit confused about the use of IV, and key hash.
Is the key hash and IV stored inside the headers of the cipher text?
Isn't it a security risk to store this header information? |
i'm working on an opensource project that AES 256 encrypts **many images with the same key** in PyCrypto, and decrypt them with CryptoJS. That's what my prototype does so far:
## General
* AES 256 mode=CBC, padding=Pkcs7
* Encrypt many images with the same salted password
* an unique iv for every image
* store t... |
We use MobilePASS at work but the latest version of the android client seems to be buggy so I wanted to have a go at implementing the algorithm myself.
You can download the client to play with here: http://www.safenet-inc.com/support-downloads/mobilepass-download-page/
It looks to be based on the HMAC-SHA256 OTP ... |
i'm working on an opensource project, a generator for static, password protected photo galleries. The generator AES 256 encrypts **many images with the same key** in PyCrypto, and decrypt them with CryptoJS. That's what my prototype does so far:
## General
* AES 256 mode=CBC, padding=Pkcs7
* Encrypt many images wi... |
i'm working on an opensource project, A generator for static (html/js), password protected photo galleries. The generator AES 256 encrypts **many images with the same key** in PyCrypto, and decrypt them with CryptoJS. That's what my prototype does so far:
## General
* AES 256 mode=CBC, padding=Pkcs7
* Encrypt many... |
I need some input on the use of HMAC-SHA256 in an open source project, any help appreciated.
The problem I'm solving is session fixation. We have a username, for that username we'd like to generate a session ID that would only be valid for that particular username so that it cannot be reused across users.
The ses... |
You're pretty much on the right track, I've got a few comments/suggestions though:
> store the plain sha1 of the unencrypted image with the encrypted image
I'm assuming the sha1 hash is to ensure the integrity of the data being encrypted? If that's the case, you should have a read through [this](http://crypto.st... |
Given a one-way compression function $h:\{0,1\}^n \rightarrow \{0,1\}^m$ and an attacker that picks $x_1 \ldots x_t \in \{0,1\}^n$ (uniformly distributed), I have to show that the probability to find a collision in the picked elements is smaller than $\epsilon$ if $m > log(\frac{t^2}{2 \epsilon})$.
Assumption: $h$ i... |
I'm storing the salted hash of a credit card number in a database. What I'd like to be able to do is determine if two different entries in the same database correspond to the same credit card. Specifically, let C1 and C2 be two credit card numbers (which may or may not be the same). Let S1 and S2 be two different salts... |
I am invesigating the AES-SIV (rfc 5054) based block cipher. The construction of the S2V is lying on the AES-CMAC and dbl and XOR operation. Given a AAD the size of L and in the 128bit block operation, I have some concern that if the L<16bytes, the initial block with all 0s input is not more than an PRF function to ge... |
When using a “sponge function” to create a cryptographic hash, we can look at the flat sponge claim, which flattens the claimed success probabilities of all attacks using a single parameter: the claimed capacity *c*<sub>claim</sub>
Is there any way to actually verify the probability of that claim - in this case: pot... |
E.g., in Python's hashlib, [update()][1] basically merges in string buffer functionality into the object. Several other digest APIs I've seen have this pattern.
Considering this adds functionality that arguably doesn't belong here, why is this pattern popular?
[1]: http://docs.python.org/2/library/hashlib.htm... |
What is the purpose of update() in popular hash APIs? |
Being able to generate hashes incrementally (by presenting parts of the string being hashed) is there for basically two reasons:
* It's commonly useful in practice. Quite often, we don't have the entire string in one contiguous segment; instead, we often have parts laying around separately. For one simple example... |
I have a data set with 300 Million entries and every 5 minutes 4000 random entries in this table change. I need to calculate the merkle root on this data set to validate integrity multiple times every 5 minutes.
Assuming sha224 hashes this would be 8 GB for just the leaf nodes and almost 16 GB of data would have to... |
I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher as secure as the original one ?
Thank you. |
I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher as secure as the original one ?
Thank you.
**EDIT**
Some missing information related to the question, according to [comment by OP](http://crypto.stackexchange.com/questions/90... |
I am a bit confused about the use of IV, and key hash.
Is the key hash and IV stored inside the headers of the cipher text?
Isn't it a security risk to store this header information?
By key hash I mean the hash of key is stored inside the headers. It seems that when I use gpg or OpenSSL , the header of cipher... |
Given a one-way compression function $h:\{0,1\}^n \rightarrow \{0,1\}^m$ and an attacker that picks $x_1 \ldots x_t \in \{0,1\}^n$ (uniformly distributed), I have to show that the probability to find a collision in the picked elements is smaller than $\epsilon$ if $m > log(\frac{t^2}{2 \epsilon})$.
Assumption: $h$ i... |
Extremely sorry for not wording the title of this question correctly, but I couldn't find the right words to word what I was trying to find out. Basically, I want to know if having a 8-byte hash value is better than 16-byte hash value.
My mind tells me that the shorter the hash value, the better. But doesn't a small... |
Is it better to have a lower hash value, than a higher hash value? |
Extremely sorry for not wording the title of this question correctly, but I couldn't find the right words to word what I was trying to find out. Basically, I want to know if having a 8-byte hash value is better than 16-byte hash value.
My mind tells me that the shorter the hash value, the better. But doesn't a small... |
Is it better to have a shorter hash value, than a longer hash value? |
In continuation to [this][1] question: which else operations are used in cryptography and why?
What is the difference between addition modulo 2 (xor) and addition modulo 2 ^ register size (addition with overflow)?
[1]: http://crypto.stackexchange.com/questions/8533/why-are-bitwise-rotations-used-in-cryptograp... |
What operations are used in cryptography and why? |
After coming back to try to finish more of my OpenPGP implementation, I refound one of my questions http://stackoverflow.com/questions/6021360/openpgp-tag-18-19-description-confusion that I am still having trouble with.
This time however, I have been able to encrypt some data and get another program to decrypt it. ... |
Intel has an on-chip RdRand function which supposedly bypasses the normally used entropy pool for /dev/urandom and directly injects output. Now rumors are going on that Intel works together with the NSA... and knowing that PRNGs are important for cryptography is enough to get this news spreading.
I personally don't ... |
> which else operations are used in cryptography and why?
This question is hopelessly broad, but I'll give the "which" a shot. Ignoring asymmetric constructions like RSA, cryptographic primitives typically stick with operations that are either a single instruction in common architectures or can be implemented cheapl... |
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