All Questions
29,862
questions
5
votes
1
answer
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Any good file format alternative to PGP for encrypting data at rest?
I'd like to create an encrypted file that:
Can be decrypted on a variety of platforms (mainly Windows, OS X, and Linux) with knowledge of the key.
Can be decrypted with existing tools (perhaps ...
- 203
6
votes
3
answers
1k
views
Using an RSA private key simultanously as an AES encryption key to generate random numbers?
Currently I'm implementing a PRNG for an embedded system. Using the RFC 4086 I've decided to use the X9.17 - to be more specific the successor X9.31- standard to implement my PRNG. X9.17 uses DES, but ...
- 141
19
votes
2
answers
3k
views
How long would the 100 Year Cryptography Project have secured its data had it been started 100 years ago?
The goal of the Tahoe-LAFS 100 Year Cryptography project is to "enhance Tahoe-LAFS's cryptographic system so that Tahoe shipped today/next year might remain safe from cryptographic attacks for a 100 ...
- 1,866
3
votes
2
answers
369
views
What is sent on the initial communication with Kerberos?
When a user wants to communicate with another user (let's say Alice and Bob), what is sent over the network during the initial communication?
Alice uses her Kerberos client and enters her password ...
- 504
5
votes
3
answers
2k
views
Is public-key cryptography the only option in this scenario?
Two parties: a client and a server are to a agree on a symmetric key. Both the client and the server are aware of a master password. The way this is currently done ...
- 1,192
6
votes
2
answers
374
views
Proof that Alternating Step Generator and modifed ASG' have equivalent security?
The Alternating Step Generator (ASG) is a PRNG combining 3 LFSRs. Output of the ASG is the XOR of the output of two clock-gated LFSRs. At each step, a single one of these LFSRs is clocked, according ...
- 139k
9
votes
3
answers
1k
views
Is there an algorithm to find the number of intersections of two sets?
Suppose both I and my friend have a set of integer numbers. We want to know the number of common elements in our two sets but without knowing elements of the sets of each other. So I don't want my ...
- 93
11
votes
3
answers
761
views
Are these emerging threats against AES affecting your designs?
Recentally, an attack on AES was discovered which reduces its computationally complexity, by a very slight amount.
The first key recovery attack on the full AES-128 with computational
complexity $2^{...
- 1,486
54
votes
10
answers
14k
views
Now that quantum computers have been out for a while, has RSA been cracked?
D-wave systems 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 ...
- 961
7
votes
3
answers
1k
views
How can two different passphrases unlock the same content?
I have heard that in enterprises it is common that the IT admin has a master passphrase that can unlock any content that an employee encrypts.
It would be temping to think, that the IT admin's ...
34
votes
5
answers
6k
views
What security do Cryptographic Sponges offer against generic quantum attacks?
In the face of non-quantum attacker, Keccak[r=1088,c=512] with 512 bits of output provides:
Collision resistance up to $2^{256}$ operations
Preimage resistance up to $2^{256}$ operations
Second ...
- 1,430
12
votes
3
answers
3k
views
Is the number of creatable torrents limited?
Currently, a magnet link containing a 40-digits long SHA-hash value, is assigned to every torrent which is created. Therefore, this hash should be unique to identify a torrent and send the right bytes ...
- 445
5
votes
4
answers
1k
views
Verify product without revealing multipliers
Situation:
Several participants contribute encrypted random numbers. These numbers will be used to generate community-agreed random (by simple multiplication).
Question:
Is there any way to detect ...
- 201
4
votes
3
answers
437
views
Where can I find useful data for cryptography/coding theory?
When implementing cryptographic/coding theory algorithms one need to use data like big prime numbers, numbers in $Z_n$ and their inverses, irreducible polynomials in $Z_n[x]$ and so on...
While ...
- 441
32
votes
2
answers
8k
views
Why can't one implement bcrypt in Cuda?
I had heard that although it's easy to implement message digest functions like MD5, SHA-1, SHA-256 etc. in CUDA (or any other GPU platform), it is impossible to implement bcrypt there.
bcrypt is ...
- 1,486
23
votes
4
answers
14k
views
What tests can I do to ensure my random number generator is working correctly?
In the past I have used the Chi-squared test to check the statistical randomness of my generator. Is this a good test to use? Are there other tests?
- 1,967
18
votes
4
answers
23k
views
What is the relation between RSA & Fermat's little theorem?
I came across this while refreshing my cryptography brain cells.
From the RSA algorithm I understand that it somehow depends on the fact that, given a large number (A) it is computationally ...
- 299
46
votes
3
answers
27k
views
What are the differences Between “White-Box Cryptography” and “Code Obfuscation”?
I have been reading the question "What is a white-box implementation of a cryptographic algorithm?" and it led to this short article / Q&A which states in question 2:
Q2: What is the ...
- 688
8
votes
5
answers
2k
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Applications of Group Ciphers
I've been reading a paper [1], and I've ran across something called a "Group Cipher", which is similar to homomorphic encryption, with an important difference.
In homomorphic encryption we have an ...
- 183
43
votes
2
answers
32k
views
What is entropy?
We discuss a lot of topics and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy ...
- 1,967
12
votes
3
answers
5k
views
Which algorithms are used to factorize large integers?
Even if RSA decided to cancel the Factoring Challenge, it seems that some teams keep working on it. According to Wikipedia, RSA-768 has been factored in late 2009.
What are the current large integer ...
- 511
117
votes
4
answers
78k
views
How should I calculate the entropy of a password?
If part of the password is a whole regular English word, does the entropy of that part depend on the number of English words in existence, the number of English words known by the choosing algorithm, ...
- 1,967
28
votes
7
answers
11k
views
Is calculating a hash code for a large file in parallel less secure than doing it sequentially?
I would like to improve the performance of hashing large files, say for example in the tens of gigabytes in size.
Normally, you sequentially hash the bytes of the files using a hash function (say, ...
8
votes
6
answers
1k
views
How can I improve a password generation scheme based on a shared secret and URL?
I currently use the following method to generate a different password on every website I have to login:
password = SHA1 ( mainPassword . domainName . number )
...
- 183
1
vote
1
answer
6k
views
The use of cribs [closed]
I'm looking to incorporate more crib usage in breaking ciphers in unknown enciphering schemes, or at least to gleam what information I may. This seems to be a big hurdle to me, and I'm looking for ...
- 2,319
10
votes
1
answer
347
views
Is the Representation Problem hard on elliptic curves?
The RP in ECC would be to find $a_1,\ldots,a_n$ (integers) given $P$ and $Q_1,\ldots,Q_n$ (points in the EC) such that $P = a_1 \cdot Q_1 + \ldots + a_n \cdot Q_n$.
Is it hard when DH-like ...
- 1,867
2
votes
1
answer
14k
views
c# Correct Triple Des Block Encryption Usage
I found the below code online, but in its original state, the encryption was not using any padding (Padding.None), and was encrypting in blocks of 8. I wasn't able to get this code to properly encrypt ...
- 21
5
votes
2
answers
5k
views
ANSI X9.9 Cryptography Standards
I'm trying to create a ISO8583 Rev93 message.
What is the standard way of generating MAC key in ANSI X9.9
DES-CBC encryption algorithm is used to encrypt the ...
- 153
13
votes
2
answers
4k
views
How should I store passwords that need to be available in plain text?
Suppose I need to store login information for a third-party website for a few users, how would I go about doing it?
Since I am logging into a third party website, I need the password in plain-text, ...
- 505
5
votes
4
answers
1k
views
Why isn't the alternating step generator used more often?
According to the Wikipedia entry for the Alternating Step pseudorandom number generator, there is no public cryptanalysis for this device since it was invented back in 1987 by C.G. Gunther. I have ...
- 491
15
votes
3
answers
858
views
Where do I securely store the key for a system where the source is visible?
I have a customer with an Access database (ugh!) in which credit cards are stored in plaintext (yikes!), so amongst other changes I'm doing in the app, I'm applying some encryption in there.
I've ...
- 253
12
votes
1
answer
16k
views
How does the index of coincidence work in the Kasiki test?
I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book (Cryptography Theory And Practice by Douglas Stinson) ...
- 121
-1
votes
2
answers
2k
views
How exactly are GPG keys (and prime numbers inside of GPG) mathematically related?
I know that the keys are somehow mathematically related, and I know that they're somehow generated via prime numbers, but how exactly are they related? I realize that it'd probably be best for me to ...
- 159
21
votes
4
answers
2k
views
How secure is the Bitcoin protocol?
Are there any evidence (other than not being cracked so far) that the Bitcoin protocol is secure? "How secure" is it?
(I realize that this might not qualify as a meaningful question - feel free to ...
- 1,007
1
vote
1
answer
2k
views
iSeries (AS/400) Database File: password encryption [closed]
I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except...
In order to allow users to login and maintain ...
- 111
7
votes
3
answers
1k
views
Is the logic for how the enigma machine worked documented somewhere?
I know that there is a formula to calculate the result of any input but is the logic of how the machine actually worked documented?
I have seen schematics for the circuitry and even a how to make ...
- 283
22
votes
1
answer
3k
views
Mapping points between elliptic curves and the integers
My primary question is:
Is there an easy way to create a bijective mapping from points on an elliptic curve E (over a finite field) to the integers (desirably to $\mathbb{Z}^*_q$ where $q$ is the ...
- 8,587
18
votes
2
answers
4k
views
Is HTTPS secure if someone snoops the initial handshake?
Let's say I'm on an open wireless network that's being actively sniffed and I connect to an HTTPS site. Even though my subsequent traffic is encrypted, couldn't the sniffer use the data from the ...
- 183
32
votes
3
answers
5k
views
Are common cryptographic hashes bijective when hashing a single block of the same size as the output?
It's been said that CRC-64 is bijective for a 64-bit block.
It the corresponding statement true for typical cryptographic hashes, like MD5, SHA-1, SHA-2 or SHA-3?
For example, would SHA-512 be ...
- 1,867
20
votes
3
answers
11k
views
Cryptanalysis to reverse engineer a hash?
I understand this may not be the best place to ask a question like this, but I believe that this community may be the best/only place I can ask such a question.
I have inputs and outputs from an in-...
- 211
13
votes
3
answers
4k
views
Is it okay to use a hash of a timestamp as the IV for AES?
The message format includes a datetime field in the clear. Is it okay to also use this field (or some hash thereof) as the initialization vector?
In this case, CBC is the mode being used.
- 233
60
votes
8
answers
60k
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How does asymmetric encryption work?
I've always been interested in encryption but I have never found a good explanation (beginners explanation) of how encryption with public key and decryption with private key works.
How does it ...
- 611
3
votes
1
answer
199
views
ID-Secret Scheme
I have an ID-Secret scheme and I'd like to hear if there are any vulnerabilities present.
Party 1 and Party 2 hold some credentials, an ID and a Secret.
Party 1 Creates this message:
...
- 1,192
9
votes
4
answers
6k
views
What alphanumeric string length can be used to guarantee no hash collisions from CRC-64? [closed]
If I'm hashing alphanumeric strings (chars in the set 0-9, a-...
- 193
23
votes
6
answers
3k
views
Can an Enigma-style cipher of sufficient complexity be considered secure today?
Regarding the German Enigma machines, if I recall correctly, the reason they were defeated was because the Allies were able to generate a massive database of possible rotor settings, and because the ...
- 505
14
votes
4
answers
2k
views
Properties of PRNG / Hashes?
There are a lot of quite elaborate PRNG's out there (e.g. Mersenne Twister et.al.), and they have some important properties, especially when it comes to crypto applications.
So, I was wondering how ...
- 283
11
votes
6
answers
12k
views
Is there any open-source white-box implementation of AES or DES? [closed]
I googled it, but got no result. There is a binary executable of a white-box implementation of DES (scroll down), but no source code is provided.
The same page also links various papers about white-...
- 3,982
89
votes
8
answers
13k
views
Guarding against cryptanalytic breakthroughs: combining multiple hash functions
Assume I want to design a protocol (or data format or similar) including some cryptographic hash, and want it to be as future-proof as possible, i.e. I want to avoid that breakthroughs in cryptography ...
- 22.6k
15
votes
1
answer
2k
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Security of N bit HMAC
Lets say that I am using 128 bit HMAC. How many operations are needed to find a "non secure" message. Is a birthday attack possible?
- 451
10
votes
3
answers
3k
views
How can my application make sure the right symmetric key is used for decryption?
I am developing an Encryption/Decryption Utility using Adobe AIR. I have chosen the AES algorithm and currently use the as3crypto library for this. My query is in ...
- 1,151