All Questions
2
votes
1answer
114 views
How to compute the dot product on encrypted values?
Is there a practical homomorphic encryption scheme that can give reasonable execution time results in computing a dot product:
$$a_1*b_1 + a_2*b_2 +a_3*b_3 +\ldots+ a_n*b_n$$
I imagine the scheme will ...
1
vote
1answer
110 views
How to calculate y value from ((y*y) mod prime) efficiently
i am working ECC-224 bit. can any one tell me, how to calculate y value from ((y*y) mod prime) efficiently for large bit numbers.
4
votes
4answers
197 views
Could a very long password theoretically eliminate the need for a slow hash?
Before I provide details, I want to clarify that I am not looking to implement this practically, but I'm only asking to get a better understanding.
The way I currently understand it, we use slow ...
2
votes
1answer
104 views
Cracking an RSA with no padding and very small e
I have a project wherein i have to crack a given cipher text encrypted using RSA and have been given N and e. Can someone suggest an RSA attack using a very small exponent e(here e=3) and no padding?
0
votes
1answer
71 views
Encrypting and Decrypting a 19-digits long BigInteger
How can I take a maximum 19-digits long BigInteger and encrypt it with the following rules:
The result must be based on digits and lower-case English letters ...
-1
votes
2answers
86 views
How does the rand() function in C work? [closed]
I want to know how rand() works (even when I don't provide any seed how it produces PRNs?) thanks!
0
votes
1answer
91 views
Sensible usecase for restricting special characters in passwords? [closed]
Please See Why Not Allow Special Characters In a Password on Security.
Several websites I've come across limit the allowed special characters for a password. My thought was, it should all be ...
0
votes
2answers
212 views
Even passwords are vulnerable to hash collision attacks?
As stated in this page large documents hashed using md5 maybe vulnerable to collision attacks. My question is even passwords of 6-30 character are vulnerable to such hash collision attacks? If yes, is ...
1
vote
2answers
121 views
Security of Deterministic Encryption Scheme
A deterministic encryption scheme is a cryptosystem which always produces the same ciphertext for a given plaintext and key, even over separate executions of the encryption algorithm.
Although we ...
6
votes
1answer
153 views
How would one crack a weak but unknown encryption protocol?
I asked a question on security.stackexchange, but was told it would be a better fit here:
http://security.stackexchange.com/questions/32779/how-would-one-crack-a-weak-but-unknown-encryption-protocol
...
1
vote
1answer
84 views
Brute forcing an HMAC
Given current technology such as GPUs and GPU cracking software I was wondering if anyone has an idea on how long it would take to brute force the key used to derive an HMAC?
2
votes
0answers
21 views
Encryption with Deduplication [duplicate]
Suppose I have a file server running ZFS with file deduplication enabled, and I have two users that are sharing files: Alice and Carol. If Alice uploads huge_file.tgz to her www/ directory, and Carol ...
-5
votes
1answer
32 views
decrypting unreadable string [closed]
Does anyone recognise this type of encryption? These are phone numbers consisting of 10 digits and starting with 0 but the encrypted text width is not 10 and does not start with the same character.
1
vote
1answer
33 views
Selecting a large NUMS Safe prime
Suppose I want to use the following simple hash function.
For a mesage $m$, take some public $a$ and prime $p$ and raise $a^m \bmod p$ (never mind the computational expense of this operation).
This ...
0
votes
2answers
91 views
Key Exchange and anonymity issue
If Alice (sender) sends a private message embedded with public key of the Bob(recipient) through onion network, so in this key exchange, does Bob remains anonymous to Alice as Alice knows about the ...
0
votes
1answer
52 views
Efficient algorithm for remainder calculation over prime field for ECC implementation?
I am working on 224-bit elliptic curve cryptography. In this 224-bit * 224-bit multiplication results 448-bit output. I am reducing 448-bit into prime field range( prime number $2^{224}-2^{96}+1$) ...
1
vote
2answers
112 views
How to verify a number encrypted with an unknown key
Are there any crypto-constructions to do the following kind of "zero-knowledge proof":
Alice encrypts a set of numbers using some cryptosystem and a secret key (e.g. Paillier crypto-system).
Bob ...
1
vote
1answer
88 views
How large should a Diffie-Hellman p be if the messages are encrypted?
How large should the prime $p$ and generator $g$ values be in a Diffie-Hellman handshake if the messages are encrypted.
If the key that encrypted the Diffie-Hellman messages becomes compromised, ...
0
votes
1answer
46 views
Solving congruences using PARI
I'm having trouble finding info in the docs about how to solve a system of congruences. The closest I can find is 'matsolvemod' in here: ...
1
vote
1answer
53 views
What is total key space in transposition algorithms
How we can measure key space in transposition algorithms? Should we specify the method, like rail fence ?
3
votes
3answers
230 views
Export from US of crypto software with key-size > 56 bits still needs permission?
Elsewhere someone stated that he couldn't publish his crypto software on the Internet, because US Export Regulations require approval, if the key size is greater than 56 bits. I know that several ...
2
votes
3answers
80 views
How comparable is OFB to a one-time pad?
This is a rather trivial question, I just want to see if I get the concept right.
In OFB you generate a pseudorandom stream based on some nonce, and you XOR that with the message to get the ...
3
votes
1answer
114 views
Understanding a Blowfish cryptanalysis
I'm reading a cryptanalysis on Blowfish, and I've come across something that I don't quite get. Let's denote
$$\delta = a \oplus a'$$
where a and a' are bytes that cause a collision in some S-box ...
4
votes
1answer
102 views
Does Linear Cramer-Shoup have pseudo-random ciphertexts?
"Linear Cramer-Shoup" is defined on pages 4 and 5 of $\:$ eprint.iacr.org/2007/074.pdf .
Are the ciphertexts in Linear Cramer-Shoup computationally indistinguishable from uniform
under a ...
2
votes
1answer
181 views
Low Public Exponent Attack for RSA
I'm having trouble understanding the algorithm for finding the original message $m$, when there is a small public exponent. Here is the example I'm trying to follow (you can also read it in the 'Low ...
2
votes
1answer
210 views
Is AES-256 a post-quantum secure cipher or not?
We know Grover's algorithm speedup brute-force attacks two time faster in block ciphers (e.g brute-forcing 128 bit keys take $2^{64}$ operations not $2^{128}$).
That explains why we are using 256 bit ...
3
votes
1answer
87 views
How to use GCM mode and associated-data properly
I'm currently migrating a project to use the bouncy castle GCM mode. I understand that using an authenticated mode removes the need for a HMAC, however I want to be sure that I'm using this mode ...
1
vote
1answer
60 views
Proof of the standard pseudorandom generator + XOR encryption scheme in Goldreich
Reading Goldreich's Foundations of Cryptography II, I found this proof for the security of the common pseudorandom generator + XOR encryption scheme (Proposition 5.2.12 in the book):
Assume you have ...
0
votes
2answers
104 views
Strong encryption done by hand [duplicate]
One of the distinguishing features of a good encryption algorithm, is that it is easy to encrypt, and hard to crack. Are there any that are easy enough for average folk to remember, and calculate by ...
3
votes
1answer
129 views
What are the constraints for an IV using AES in CBC mode?
I'm designing a protocol for use into a VPN software.
The VPN frames are encapsulated into AES-256 CBC encrypted frames. I understand that IVs must be uniquely used for each message encrypted with ...
0
votes
1answer
140 views
Anonymity in end to end encryption
Considering a scenario of anonymous data transfer between seller and buyer using proxies. If we consider that there are three proxies that are being selected by buyer to obtain data from different ...
3
votes
1answer
90 views
When confusion is applied during encryption?
I know confusion is used in cryptography to make it more difficult to identify any
relationship between the ciphertext and the symmetric key. I want to know when the confusion is applied during ...
3
votes
1answer
104 views
BCrypt vs Key Stretching MD5
Ars technica posted an article about the latest in cyber warfare from the stuxnet crew.
They key stretched MD5 by iterating it 10,000 times. It seems to be effective at handicapping HashCat's gpu ...
1
vote
4answers
100 views
How to perform Multiplicative Inverse Modulo in IDEA
How to perform the Multiplicative Inverse Modulo in International Data Encryption Algorithm?
I cannot understand on how to perform it...
ex. I have a value of "cf80" and the value that is appearing ...
3
votes
1answer
77 views
Key collision in scrypt and hkdf
I am developing a mostly-offline authorization system that authorizes a user using an deterministically generated AuthKey derived from a MasterKey derived from a high-entropy chunk of data (128 bits) ...
2
votes
1answer
106 views
DLP based crypto systems with multiple independent generators
One example of a DLP based crypto system (or rather DDH based crypto system) where the public key parameters include two independent generators of the subgroup, is Cramer Shoup. Since the security ...
1
vote
0answers
34 views
Can a LIRA system work with cjdns or other decentralized meshnets?
LIRA (Lightweight Incentivized Routing for Anonymity) is a scheme to incentivize participants in Tor to contribute resources, in particular bandwidth.
The paper talks about it being used for Tor. Can ...
0
votes
0answers
54 views
What is the significance of i^Q mod P = 1 and are there any special properties to be aware of?
I'm studying UProve, and one of the fundamental components of this technology is based upon the relationship between
i^Q mod P = 1
Lacking a specific name I can call this mathematical ...
1
vote
1answer
84 views
Partial decryption of large file in AES-GCM (or other modes)?
Lets assume
a 4gig file that is internally made of 1 million pages of 4k bytes each (page).
the file was originally AES-GCM encrypted
these pages (or entire file) lives across the internet i.e. ...
3
votes
2answers
159 views
What crypto system allows for 3 parties: Party 1 who makes an assertion, Party 2 mutates the assertion, Party 3 validates it
I'm looking for the cryptographic equivalent of a Drivers license where the issuer can be verified, the issuer doesn't need to know who you showed the drivers license to, but also allows ...
1
vote
1answer
65 views
How to obtain a one-value share in Shamir's secret sharing
This is a trivial question, but I had to ask:
since each generated share in a Shamir's secret sharing scheme initially consists of a pair of values (representing the coordinates of a point on the ...
2
votes
1answer
151 views
Encrypting many small messages (log-lines)
What would be the best way of encrypting small mesasages to be stored in encrypted form? (This sounds like somthing a textbook would cover, but I haven't found any references).
Let's say I have many ...
1
vote
2answers
208 views
Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety?
The system requires to be as paranoid as possible regarding security. One of the few contemplated changes to the current design is to use multiple encryption. First proposal was to use Serpent on top ...
1
vote
1answer
65 views
Isn't the structure of a potential plaintext of a ciphertext generated by a one-time pad dispositive, cryptanalysis-wise?
That is, if I generate every possible result, and analyze the structure against, for example, a dictionary, won't that identify which of the solutions in the domain is most likely the correct one?
I ...
0
votes
0answers
57 views
Method and explanation for calculating difference in speed between DES and RSA
Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could ...
1
vote
2answers
180 views
Diffie-Hellman key agreement with both Server Authentication and Perfect Forward Secrecy
I am trying to find the protocol with the least overhead, which still meets the following requirements:
Server Authentication of server identity to client. The client has an authentic copy of the ...
0
votes
1answer
95 views
Is there an efficient way to hide the encrypted plaintext length with a block cipher?
In block cipher modes of operation for encryption on input of a plaintext of $N$ blocks (We assume that the input size is always a multiple of the blockcipher mode: $N·16$ bytes) the size of the ...
0
votes
0answers
74 views
computing inverses in truncated polynomial rings manually for NTRU encryption
Can someone explain how to find inverses in truncated polynomial rings manually (i.e. on pen and paper)?
As an example from the tutorial:
Example. Take $N=7$, $q=11$, $a=3+2X^2-3X^4+X^6$. The ...
-2
votes
2answers
142 views
Where to store the private key and the public key in a communication protocol
I want to create a simple secured connection protocol over TCP/IP.
I just want to connect from my mobile device to a server securely.
Firstly I thought to use an SSL connection, but I changed my ...
3
votes
2answers
71 views
Current Status of mixnets for voting
I am currently doing some research on universally verifiable mixnets, but it seems to me that there are too few papers about them after 2006 or so and most of them come from the team of Douglas ...
