All Questions
1
vote
1answer
16 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
0answers
22 views
Algorithm Design for only Mutual Information Sharing [closed]
Possible Duplicate:
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 ...
0
votes
0answers
18 views
Reference Request - Performance of Encryption Algorithms [closed]
I'm looking for a good published reference that gives performance metrics on various encryption algorithms.
Can someone please point me to some references?
Are there some standard articles?
Thanks.
...
2
votes
2answers
45 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
53 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
2answers
23 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 ...
-1
votes
1answer
59 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
55 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
114 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
0answers
34 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. ...
2
votes
1answer
78 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 ...
3
votes
1answer
104 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.
WOYFN ZCMSH VUVTG BFUTW ABTZP FHIMF TFOSU UXFQC HKVKG MPUUQ MHRXI OVBRZ ...
1
vote
1answer
40 views
Can A PRNG Be Used To Generate Multiple Private Keys for ECDSA?
Suppose Alice seeds a cryptographically strong Pseudo Random Number Generator with a truly random number, and keeps it secret. Alice then uses the output of the PRNG to generate several 256-bit ...
3
votes
1answer
70 views
Is XOR in a CBC-like mode secure?
Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively.
The first byte of ciphertext is computed like this:
$C_{1} = K_{1} \oplus P_{1}$
...
1
vote
2answers
53 views
Initialization vector length insufficient in AES
I use AES with AES/CBC/PKCS5Padding with the following encryption and decryption code sections in Java:
cipher.init(Cipher.ENCRYPT_MODE, keySpec, new IvParameterSpec(IV1));
...
2
votes
1answer
75 views
How were the AES key and block length subsets of Rijndael selected?
My intuition tells me it's a trade off between speed and security, but how did the standardisation process select these three seemingly arbitrary key lengths (namely, AES-128, AES-192, AES-256).
3
votes
3answers
141 views
Is it fair to assume that SHA1 collisions won't occur on a set of <100k strings
I'm building a system that has to take file paths, and generate a unique name for each one. I'm planning on using SHA1 as the hash function. My question is: do I have to deal with possible collisions ...
1
vote
2answers
78 views
Why DSA cannot be used for encryption?
Here it is mentioned that DSA cannot be used for encrypt. But Both RSA and DSA can be used to generate public and private keys, right? (Or am I wrong?). Then why can't I use the DSA public key to ...
0
votes
0answers
58 views
Academic papers on GPU password cracking? [closed]
Are there any scientific papers or publications on GPU password cracking?
2
votes
1answer
153 views
Chinese Remainder Theorem and RSA
Wikipedia has a nice section regarding the speedup of the RSA decryption using the Chinese Remainder Theorem here. I need to understand the implementation of a similar speedup for the encryption ...
4
votes
3answers
104 views
Encryption with “constant” initialization vector considered harmful
I try to get the full reasoning behind the above statement. First, after reading articles here and at wikipedia i understand that using an IV only once is good practice.
For stream ciphers not doing ...
-1
votes
1answer
54 views
How can we find Public key have only 8 or 16bits? How many messages does Eve need to know the Public key in RSA?
Suppose Alice sends messages to Bob by encrypting the messages with Bob's public key.
Eve knows that the data is encrypted using RSA, but does not know the public key. Can Eve figure out the public ...
0
votes
1answer
47 views
How does one implement the Inverse of AES' MixColumns
I got an answer in the related question about Mixcolumn for encryption, but how about decryption?
what will I do?
Because it said that I will used this:
During decryption the Mix Column the ...
3
votes
1answer
103 views
How can disk encryption systems (like Truecrypt) resist frequency analysis when they allow random access?
I don't understand how disk encryption (e.g. TrueCrypt) is supposed to resist frequency analysis.
If blocks can be randomly accessed (which they can), doesn't that mean that frequency-domain ...
2
votes
0answers
45 views
RSA reencryption scheme
Is there such an algorithm that would allow to upgrade the encryption of a RSA-encrypted message without revealing the plaintext to the untrusted user?
Basically, such an algorithm would probably be ...
1
vote
0answers
79 views
Is it possible take a piece of data in secret?
I want something like this, but in a digital sense:
You and others walk into a room. Everyone knows who each of you are and everyone is doing their best to figure out what piece of paper each ...
1
vote
1answer
79 views
How many RSA keys before a collision?
I was wondering how many possibilities of private/public keys there are? If a million people for whatever reason tried to generate 5keys each in the same minute (on the same date and time) is there a ...
0
votes
1answer
42 views
Recovering the key in an ElGamal Signature Scheme variant
From page 318 in Stinson's "Cryptography: Theory and Practice", question 7.3:
Suppose that Alice is using ElGamal Signature Scheme. In order to save time in generating >the random numbers k that ...
2
votes
2answers
103 views
Order of hashing concatenation
A = hash("blue" + X);
B = hash("pink" + X);
If A and the literals are known and X is unknown, are there attacks on B aside from the attacks on directly on hash()? In other words, is B safe?
Would ...
1
vote
2answers
83 views
How do I demonstrate that a PRNG not designed for cryptography is not suitable for generating passwords?
This is a replication of this question on Stack Overflow. There's class Random in .NET runtime which is designed for use as a cheap fast source of pseudo-random numbers for simulation - very fast, ...
1
vote
1answer
82 views
Public Key Encryption with forward secrecy
Is there a known non-trivial system with plausibly secure public key encryption where:
1. $\;\;$ the $\:$ time $\:$ function is efficiently computable
2. $\;\;$ [pubkey,privkey] $\:$ pairs are ...
0
votes
0answers
50 views
Search tool to identify which algorithm is in use
I'm trying to identify what algorithm is encrypting / encoding / hashing passwords in a client system. I have samples of matching plaintext and ciphertext. Is there a search engine somewhere that will ...
3
votes
1answer
66 views
Do public/private pairs work both ways?
Public/private key algorithms such as RSA encrypt a message with a private key but only decrypted with another (mathematically related) key.
Can the public key decrypt the messages encrypted with ...
1
vote
1answer
94 views
OTP from Sony BIOS password recover
From Dogbert's blog:
Sony has a line of laptops ("Vaio") which compete mainly in the high value market segments. They implemented a master password bypass which is rather sane in comparison to the ...
5
votes
2answers
87 views
Is my HMAC secure if I have a complete series of HMAC'd prefix strings
Let's say I have a long sentence, like "The quick brown fox jumped over the lazy dog." Let's further say that I need to keep this string encrypted, so I use an HMAC. Let's further further say I want ...
-3
votes
0answers
44 views
Security of Files [closed]
How do attacks penetrate files? Please provide the details as well as the process.
How to ensure security of files against file attacks.
list of file attacks
This can help me, for me to proceed to ...
4
votes
1answer
96 views
Generating Random Primes
Although this has been extensively discussed around here, I'm curious whether my approach makes sense, or I should just stick to "the standard version".
I'm implementing some homomorphic encryption ...
0
votes
1answer
36 views
Attack to avoid by the used of OFB(Output Feedback Mode)
What other attack can avoid by the used of Output Feedback in an algorithm?
1
vote
2answers
50 views
Complexity of ECB and OFB
What is the complexity of ECB in terms of Time and Memory?
and also in OFB? I can't find it in the internet, so I decided to ask it in here.
2
votes
4answers
112 views
Creating an encryption key from several other keys and using hash functions
When we want to combine two (or probably more) keys to create a single encryption key that relies on all of them, what is the proper method for doing that? Simple XOR? Using hash functions? ...
I ...
-1
votes
0answers
41 views
Advanced Encryption Standard(Rijndael) Security [closed]
Possible Duplicate:
How secure is AES-256?
How really secured Advanced Encryption Standard(Rijndael)? with some scientific explanation. that's why they come up to used it to protect top ...
5
votes
2answers
178 views
Can two different pairs of RSA key have the same modulus?
Can $n=pq$ be part of two different pairs of RSA keys?
If such keys exist, say $(e_1,n)$ and $(e_2,n)$, how are they related?
What will be the security concerns for the two users?
-1
votes
0answers
24 views
Rijndael as the Advanced Encryption Standard [closed]
Possible Duplicate:
Rijndael vs. Serpent vs. Twofish: General comparison
Why Rijndael was became the Advanced Encryption Standard? what is the basis of NIST?
9
votes
6answers
210 views
Can I encrypt user input in a way I can't decrypt it for a certain period of time?
I run a baseball league and would like to do silent auctions for free agents. This would require teams to enter their highest bid and the highest bidder at the end of the auction period would win. ...
5
votes
1answer
66 views
One-way hash on encrypted data, result hidden from hasher
I'm looking for a one-way hash function that can be performed by A on an encrypted piece of data E(D) provided by B, without the performer A able to figure out D or H(D). This similar to HMAC(Message, ...
4
votes
2answers
60 views
Practical necessity of semantic security under chosen plain text attack (CPA) in CBC mode
I was not able to understand why we practically need a CPA security in Cipher Block Chaining. (which insist on having a random IV), let say if the encryption is not CPA secure i.e , the adversary can ...
3
votes
1answer
79 views
Has there been any cryptanalysis of RC4-52?
Several websites ( such as Is there a secure cryptosystem that can be performed mentally? ) briefly mention RC4-52 as a modification of standard RC4.
RC4-52 has only with 52 instead of 256 elements ...
5
votes
1answer
76 views
Digital signature for an expiring password
I would like to create a publicly available tool that is used to generate a password that gives a limited time access to a resource.
My idea is to digitally sign the current date with a private key ...
6
votes
1answer
96 views
A fair peer-based coin-flipping protocol?
I found this question on the game programming site and was intrigued. I came up with an answer off the top of my head but I'm no cryptanalyst so it is probably not water-tight.
This is how my idea ...
1
vote
0answers
33 views
Comparison: complexity measures vs. security
Assume that you want to compare several cryptographic primitives (say, encryption schemes), and choose one. You need to consider several complexity measures, such as the key length, encryption time, ...
