All Questions
4
votes
1answer
221 views
OpenPGP Signature Packet hashed data
RFC 4880 describes the version 4 signature packet, tag 2, as
...
0
votes
1answer
104 views
RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?
Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a ...
9
votes
1answer
184 views
Which MACs can be converted into a secure unkeyed hash function?
It is known that setting the secret key to a fixed, public value does not make MACs like CBC-MAC or GMAC into secure unkeyed cryptographic hash functions that could be used - for instance - for ...
2
votes
3answers
200 views
Algorithm to securely exchange identities
Say four people each have a public/private key pair that they can use to encrypt or sign messages. They have an anonymous way to post messages such that the others can see them. Malicious entities can ...
1
vote
2answers
160 views
Brute force a ciphered message?
I wrote my own cipher to encrypt messages. I would like to test a sample ciphered message to see how strong it is. Are there any tools for such task either in Windows or Linux ?
3
votes
1answer
195 views
Is quantum key distribution safe against MITM attacks too?
i read this recently: http://www.newscientist.com/article/dn12786-quantum-cryptography-to-protect-swiss-election.html
and some parts of this: http://en.wikipedia.org/wiki/Quantum_key_distribution
...
3
votes
1answer
233 views
Do Cryptographic Hashing Algorithms operate only on Integers?
Do all the Cryptographic hashing algorithms operate only on integers (32 bit or 64 bit)? Is there any operation performed on Floating Point Numbers as well?
The reason I ask this is because I read ...
2
votes
1answer
716 views
In which order are the round keys used during AES decryption?
In the Add Round Key step in AES decryption, which part of the expanded key will I XOR first to the result of the SubBytes step?
Is it the 10th round key?
For example, is this the right order?
...
1
vote
3answers
200 views
Does the MixColumns step come before or after AddRoundKey in AES decryption?
I found these images depicting the AES decryption process:
In the first image, the MixColumns step comes before the AddRoundKey step, while in the second image, the AddRoundKey will come before ...
2
votes
1answer
267 views
What is the harm if I publish an encrypted RSA private key publicly?
What is the harm if I publish an encrypted RSA private key publicly? Or in this case, what is the harm if I publish many thousands or millions of them?
Assuming that the private key is encrypted ...
1
vote
2answers
104 views
Standard symbol / notation for “x knows y”, or the inverse
What's the standard way to express "$x$ knows about $y$", or "$x$ has no knowledge of $y$" in cryptographic notation?
Example (PRNG predictor):
$\exists f : P(f(G(k)|_{0..n}) = G(k)|_{n+1}) \geq 0.5 ...
2
votes
1answer
286 views
Linear Feedback Shift Register Taps
Linear feedback shift register tap charts are availale for registers of length 3 to 168. Does anyone have a chart for register lengths from 168 to 256 or beyond? Thank you.
3
votes
5answers
818 views
Galois fields in cryptography
I don't really understand Galois fields, but I've noticed they're used a lot in crypto. I tried to read into them, but quickly got lost in the mess of heiroglyphs and alien terms. I understand they're ...
3
votes
1answer
185 views
Memory-hard operations in work-factor hash functions
I'm playing around with work-factor hash functions, and I'm looking for a memory-hard operation to make it resistant to GPU / parallel hardware attacks. I considered a very large (i.e. 64K) s-box that ...
4
votes
2answers
253 views
After implementing a novel encryption algorithm, how would one go about analyzing its security or get help from others in doing so?
Preface: This question was originally asked on Theoretical Computer Science and later on Computer Science. The kind people on cstheory.SE referred me to this web site. It is being repeated here in an ...
1
vote
1answer
161 views
2
votes
2answers
183 views
How can encryption involve randomness?
If an encryption algorithm is meant to convert a string to another string which can then be decrypted back to the original, how could this process involve any randomness?
Surely it has to be ...
0
votes
0answers
73 views
Is this a secure multiparty protocol?
I am facing the following situation and i am trying to break down the problem into some specific cryptogrphic primitives.
There is a function F that takes as input a bit string and produces a ...
0
votes
1answer
175 views
Why does my implementation of CBC mode only decrypt the first block correctly? [closed]
I have the following code that uses a CBC mode to encrypt a text by dividing it to 3-elements block. But it only works correctly on the first block which is xored with the IV.
...
0
votes
1answer
118 views
ECDSA - point order criterion
i am creating some primitive demostration for ECDSA over small curve ( p < 229). But my implementation have some weird issues. Verify process return false even if the signature is correct. Because ...
0
votes
0answers
48 views
what is the required protocols to make share the key? [duplicate]
Possible Duplicate:
gererating session key using diffie hellman algorithm?
The first subnet have three nodes (A,B,C) they are connected to second subnet via (C-E), the second subnet consist ...
2
votes
2answers
115 views
Is the “Signed on date” of a PGP Signature Verified?
I noticed that PGP signatures have a "signed on" field. I was wondering if this is "trustworthy" information and if so how is it accomplished.
For example, I can't see how it could be trusted ...
9
votes
2answers
316 views
Is every output of a hash function possible?
Is every output of a hash function (e.g. SHA1, MD5, etc) guaranteed to be possible, or, conversely, are there any output values that cannot possibly be created from any input? If so, what guarantees ...
6
votes
2answers
235 views
Attacks of the MAC construction $\mathcal{H}(m||k)$ for common hashes $\mathcal{H}$?
Consider a common practically-collision-resistant Merkle–Damgård hash function $\mathcal{H}$ (e.g. SHA-1, RIPEMD-160, SHA-256, SHA-512). We define a Message Authentication Code $\mathcal{C}$
$$(k,m) ...
4
votes
1answer
185 views
Is it secure to use the hash of key as the IV in AES encryption?
I need to store some sensitive data for a program. For each copy of the program, there will be a unique key for encrypting one (and only one) file using AES encryption (OFB). The key will not be ...
6
votes
2answers
374 views
Hash decrypts key, key decrypts cipher… why?
I noticed recently that a couple of pieces of encryption software (TrueCrypt being one of them) don't directly use a hash of the password as the key for the block cipher. Instead, they generate a ...
0
votes
2answers
299 views
What is the time complexity of the RC4 encryption & decryption algorithms?
I'm trying to figure out what the time complexity of RC4 encryption & decryption algorithms is, in big-O-notation.
0
votes
0answers
221 views
How to calculate a key for Hill Cipher? [closed]
I need an easy way to calculate 3X3 key matrix to encrypt a 256 characters text ?
0
votes
2answers
69 views
Encrypting documents through a proxy key
Suppose I'm developing an app to secure a lot of documents. These documents were encrypted (say, using AES) with a key X.
This key X is basically the password that the user enters before wanting to ...
1
vote
4answers
393 views
Is my pseudo-random initialization vector secure?
How can I know if I am generating a secure pseudorandom initialization vector?
Currently I am planning to generate a pseudo-random initialization Vector using current date and time - is this secure ...
2
votes
0answers
127 views
Safe generator for ElGamal signature
What are the properties a generator $g$ should have to be secure for ElGamal signatures (original scheme)?
I am aware that it is poorly chosen and not secure when $g|p-1$ or $g^{-1}|p-1$, where $p$ ...
4
votes
3answers
277 views
Order of cascaded ciphers
Does the order of a block cipher cascade (e.g. in TrueCrypt) make a difference to the security provided, assuming independant keys?
For example:
...
3
votes
1answer
112 views
DGK Cryptosystem Key Generation and Decryption Issues
I detailed here the DGK (Ivan Damgård, Martin Geisler and Mikkel Krøigaard) cryptosystem, and I managed to get it to work, most of the time...
The BIG problem that I am facing at the moment is that ...
3
votes
2answers
301 views
How were the number of rounds for different key sizes of AES selected?
The number of AES rounds increases with the key length. Why increase the number of rounds at all, and how were these round counts chosen?
2
votes
0answers
74 views
XSLT tranform in xmlsignature form, a part of xmldocument? [closed]
I have a HTML page(A Form) where user will enter his details. Details to enter are NameagesalarystateCity Now when user enters all details and click Button then I will create xml file containing the ...
2
votes
1answer
169 views
Finding a solution to a (sort of) discrete logarithm by asking questions
Let $p = kq + 1$ and $q$ be primes such that $log$ $q = n$, $log$ $k = n$ and such that the bit size of every prime factor of $k$ is bounded
by $log$ $n$. Let $g$ be a generator of the unique ...
0
votes
1answer
268 views
How do I generate a session key using the Diffie Hellman algorithm?
How to generate a session key between two nodes in two different subnets when the nodes don't know each other directly, using diffie hellman algorithm?
3
votes
0answers
213 views
Why do new versions of TLS use an explicit IV for CBC suites?
SSL 3.0 and TLS 1.0 used an insecure scheme to generate implicit IVs when encrypting records in CBC mode: They used the last part of the previous record, a value that can be predicted by the attacker. ...
2
votes
2answers
253 views
Lamport signature: How many signatures are need to forge a signature?
Lamport signature: Signing the message Note that now Alice's private key is used and should never be used again. The other 256 random numbers that she did not use for the signature she must never ...
-2
votes
1answer
532 views
Cryptography for kids [closed]
My daughter has been playing on the NSA's web page called CryptoKids but I was wondering if there is anything else out there that is may be more challenging to a nine year old.
Books are good, ...
1
vote
1answer
180 views
ECIES protocol - what does the || operation mean?
I am studying elliptic curves problems, which also includes study of related protocols such as ECIES. A there is a problem I don't understand operation $||$. What this operation mean?
Some stuff is ...
2
votes
2answers
152 views
Algorithm Design for only Mutual Information Sharing
Bob and Alice each have a bit string they want to keep private. They each want to know what the bitwise AND of their two strings would be without telling the other or anyone else listening to their ...
1
vote
2answers
233 views
Real life collision when only using truncated hash
For MD5 two different inputs are known that produce the same 128 bit hash value. However, these inputs are artificially created for this specific purpose.
For normal, real life inputs I believe no ...
0
votes
1answer
120 views
NTRUEncrypt - Choose the initial random polynomial
I'm trying to implement NTRUEncrypt but encounter some problems. I've finished all the basic functions that are needed for the scheme base on this Document, but I can't find an algorithm to check the ...
0
votes
1answer
110 views
amateur cryptosystem -> a very long boolean expression -> attempt to reduce it [closed]
(newbie here) I try to analyze amateur cryptosystem and wondering, if it's possible to reduce it as reduce a very long boolean expression? What tool can I try to use?
2
votes
1answer
224 views
DGK Cryptosystem Encryption Speedup
Following @poncho's nice clarification of the RSA speedup here, let's see if I'm able to do the same in the case of the DGK cryptosystem:
We have pk = (n, g, h, u), sk = (p, q, $v_p$, $v_q$) which ...
3
votes
2answers
456 views
Difficulty of breaking RSA for a given key size
Is it true that breaking a 1024-bit RSA key is as difficult as breaking a 128 bit symmetric key (e.g. AES)? I know that breaking a RSA key is equivalent to factoring the modulus $N$. To factor it, you ...
0
votes
1answer
79 views
Determine complexity of a SAT problem
Is there a standard way to determine a complexity of the specified SAT problem? I'm researching algebraic cryptanalysis and came to solving multivariate quadratic equation systems using CryptoMiniSat. ...
6
votes
1answer
370 views
Why Addition Mod 32?
I was looking at the algorithm for Twofish, and I noticed that in some places a XOR is used, but in others, they use "addition modulo-32." What makes modulo-32 special? Why not always use XOR? Why not ...
5
votes
2answers
561 views
Assistance Cracking Classical Cipher
Below is the cipher text I am trying to break and as you can see its rather short which is why I am having so much trouble.
...
