5
votes
2answers
151 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 ...
3
votes
2answers
148 views

Could this be a valid variation of the Schnorr protocol?

The Schnorr protocol is a 3-steps proof of knowledge of a discrete logarithm, whose interactive version works as follows. Let $p$ and $q$ be two public primes, such that $q \mid (p-1)$, and let $G$ ...
0
votes
2answers
181 views

Is there a way to encrypt multiple sets of data into one result, with separate keys decrypting each set of data

What I am picturing is something like this: Block A: "Hello, how are you today?" Block B: "The weather reminds me of summer." I encode this, giving me two keys and a resulting encrypted block e.g. ...
6
votes
2answers
797 views

Vulnerabilities if encrypting the same data with 2 different keys

Let's say that Alice and Bob complete a key exchange and then Alice uses that key k1 to encrypt a 256-bit key kaes1 and sends it ...
2
votes
1answer
412 views

Do companies like CipherCloud really have the option to use homomorphic encryption?

I was reading How is CipherCloud doing homomorphic encryption? and was wondering: Is there a technically feasible way for companies like CipherCloud to use homomorphic encryption (HE) while ...
0
votes
1answer
219 views

What does the cipher-text overhead means?

I have two questions here. What does the cipher-text overhead means? Why we were suggested not to encrypts the plain-text itself instead just encrypts only the key (i.e random number)
1
vote
2answers
247 views

What security flaw exists in MAC authentication scenario?

What security flaw exists (if any) in the solution of this non-encrypted authentication scenario? An unencrypted message passes one-way from computer A to B. Its transmission is viewable by the ...
8
votes
2answers
2k views

Pre-image resistant but not 2nd pre-image resistant?

Are there any cryptographic hash functions for which there is a known pre-image attack, or a known second pre-image attack, but not both? The attack doesn't have to be practical - just anything that ...
1
vote
1answer
99 views

security amplification

Reading some papers on security amplification of weak-PRP written by Stefano Tessaro, I noticed the use of notion "epsilon-PRP" and the notion of "security amplification". These notions, in ...
0
votes
2answers
362 views

Cryptographic Symmetric Stream Cipher

Let me know a cryptographic symmetric stream cipher system with only two functions say S() and P() and it should satisfy the ...
1
vote
1answer
131 views

Random decomposition of symmetric key

Considering a symmetric cipher (i.e : AES in counter mode), is it possible for any given key to be randomly decomposed into other keys without knowing the message or the ciphertext, such as : ...
5
votes
2answers
851 views

How does one calculate the cryptoperiod?

NIST Special Publication 800-57 defines a cryptoperiod as the time span during which a specific key is authorized for use by legitimate entities, or the keys for a given system will remain in ...
5
votes
1answer
261 views

Why is the Pedersen commitment computationally binding?

This is how the Pedersen commitment seems to work: Let $p$ and $q$ be large primes such that $q \mid (p-1)$, let $g$ be a generator of the order-$q$ subgroup of $Z_p^{\star}$. Let $a$ be a random ...
4
votes
2answers
236 views

How to use salt when there is only one user

I am encrypting files for storage in an untrusted location, using a custom Java program to do that. There is only one user, but there are many files. I am using AES in CBC mode with PKCS5 padding, and ...
1
vote
2answers
567 views

Is it possible to subtract/multiply numbers using homomorphic encryption?

Most of the libraries I've seen allow you to add encrypted numbers. Is it possible to subtract and multiply them?
2
votes
1answer
187 views

Public Keys on Social Media

Is there any problem with using social media (i.e. Facebook) as a directory of public keys? For example, couldn't Alice put a note containing $(g^a \bmod p, g, p)$ on her Facebook page so she could ...
10
votes
1answer
2k views

Technical details of attack on Android bitcoin usage of SecureRandom

Reports are surfacing that Android's Java SecureRandom class has issues and isn't totally secure. A specific example of how this issue translates to applications is bitcoin, where reports are stating ...
0
votes
1answer
424 views

How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
3
votes
2answers
2k views

Decrypting DES with decrypted and encrypted data [duplicate]

I got two 8-byte strings. One which is decrypted is: FF FF FF FF FF FF FF FF and one which is encrypted is: ...
3
votes
1answer
7k views

How does DES decryption work? Is it the same as encryption or the reverse? [duplicate]

If DES decryption is the same as encryption done in reverse order, then how can the reversed S-Box convert 4 bits into 6 bits?
3
votes
2answers
215 views

Does impersonating an SRP server give you enough information for an off-line dictionary attack?

In a comment to an answer I wrote to another question, CodesInChaos wrote that: "Problem with SRP is that an attacker who impersonates a server learns the password hash, enabling offline search." ...
4
votes
1answer
351 views

How Were secp*k1 elliptic curve generators chosen?

The Koblitz elliptic curves specified in the SEC2 document https://docs.google.com/viewer?url=http%3A%2F%2Fwww.secg.org%2Fcollateral%2Fsec2_final.pdf all have the nice feature that the parameters are ...
9
votes
2answers
736 views

Can AES decryption be used as encryption?

Definition E: AES encryption D: AES decryption x: plain text y: encrypted text k: key In original AES cipher, encryption: y = E(x, k) decryption: x = D(y, k) Then I define the "reverse AES ...
2
votes
2answers
229 views

What is the fastest elliptic curve operation f(P) in affine coordinates such that f^n(P)=P only if n is large?

I'm working with the affine representations of points of the Secp256k1 elliptic curve (from Bitcoin). I've read many papers that show that computing some functions, like $f(P)=3P$ can be computed ...
3
votes
1answer
249 views

iOS Data Protection: What is the Input of the LFSR?

Every time a file on the data partition is created, Data Protection creates a new 256-bit key (the “per-file” key) and gives it to the hardware AES engine, which uses the key to encrypt the ...
1
vote
1answer
628 views

How to supply the GCM authentication tag to the OpenSSL command line tools?

I'm using AES-256-GCM for authenticated encryption. In order to decrypt, the ruby OpenSSL library requires an auth_tag parameter (in addition to the key and iv). ...
15
votes
3answers
2k views

Can ECDSA signatures be safely made “deterministic”?

Using the terminology of the ECDSA wikipedia page, ECDSA (and DSA) signatures require a random k value for each signature which ensures that the signature is different each time even if the message ...
1
vote
1answer
272 views

why AKS is so slow in practice? [closed]

This note (http://maths-people.anu.edu.au/~brent/pd/primality4.pdf) states that AKS is not practical. However, it is known that AKS runs in polynomial-time, and I cannot understand where the slowness ...
5
votes
2answers
2k views

AES plaintext is smaller than 128 bits - how to expand?

We are currently developing a little AES implementation in a crypto-course at university. As far as I know, AES uses a 128 bit block length, so all data that will be encrypted gets split up into ...
2
votes
1answer
216 views

Is this method of deterministically using CBC secure?

I'm trying to design a deterministic encryption scheme to enable searching in untrusted databases with the smallest possible IV overhead on ciphertexts. I know it's very bad practice but unfortunately ...
3
votes
1answer
146 views
6
votes
2answers
2k views
9
votes
1answer
6k views

How strong is the ECDSA algorithm?

Some cryptographic algorithms are as strong as the size of their key is, while other have some weaknesses that limit their strength (such as SHA-1). How strong is the ECDSA algorithm, and does that ...
2
votes
3answers
1k views

why DES encryption uses different modes like ECB,OFB?

As without using modes we can also encrypt and decrypt data then what is the need of using modes in DES?
2
votes
1answer
151 views

Can an encrypted nonce be used for authentication?

Would a scheme like the following work to allow authentication of a sender: A nonce is appended to data, and the result is encrypted. The encrypted pack is sent to the other party. The sender then ...
3
votes
3answers
245 views

Allowing the user to choose the hashing formula at the registration

I was thinking of a potential new way to increase someone's account security. The idea was allowing the user to choose one of the hash formulas available in the software (example: "MD5", "SHA512" and ...
2
votes
1answer
144 views

Can OTP still be broken if there are several messages being sent with only a slight variation in a password?

If an attacker were able to get a hold of 2 encrypted messages that were both encrypted in a one time pad with a password that were each similar but had one change in the first character, could it ...
0
votes
0answers
79 views

Why is Merkle-Damgård construction insecure? [duplicate]

I've been reading about SHA-1. I read that SHA-1 is insecure as it uses the Merkle-Damgård construction and the Merkle-Damgård construction is — according to Wikipedia — susceptible to a variety of ...
7
votes
2answers
771 views

Is FIPS 140-2's “Continuous random number generator test” practical?

Section 4.9.2 of FIPS PUB 140-2 specifies, amongst other things, a "Continuous random number generator test." Here are the relavant bits: If each call to a[n] RNG produces blocks of n bits ...
2
votes
3answers
122 views

Securing content and login with “same” password

I'm writing a client application that wants to store some secret information with a storage service. The client has to authenticate the user with the service and the service should not be able to ...
3
votes
2answers
3k views

How to perform file encryption using 128-Bit AES?

I am confused, how can I encrypt a file using 128 Bit Advanced Encryption Standard? Do I need only to encrypt the file name and it's content or is there something that I need to do to encrypt it? Is ...
0
votes
2answers
257 views

How secure would this code be against cryptanalysis?

Simple version: Create software that takes a database of the dictionary, alphabet, and phrases. Randomly generate a database of random strings of letters/numbers/symbols of varying length. Randomly ...
9
votes
2answers
612 views

Efficient Incremental Updates to Large Merkle Tree

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 ...
11
votes
2answers
1k views

Practical consequences of using functional encryption for software obfuscation

I came across this article, which describes a method, developed by UCLA CS professor Amit Sahai et al, for using functional encryption in order to achieve software obfuscation. The paper that the ...
2
votes
1answer
168 views

Generating non-supersingular elliptic curves for symmetric pairings

I am looking into the application of pairings in CPABE in particular. I've notice that the scheme uses a supersingular curve as the basis of the pairing. Looking through Ben Lynn's thesis for the ...
3
votes
1answer
164 views

salting with password hash to improve security?

Would something like the following improve security (against rainbow attacks, not brute force)? Assume that $P$ is a user-chosen password, and the objective is to obtain a hash $H$ for password ...
4
votes
1answer
199 views

Swapping Key and IV in AES? Safe?

I have an application where I want to be able to send an encrypted file, and then mete out "keys" that allow the receipient to decrypt the file from a certain point to the end of the file. Actually, ...
3
votes
2answers
152 views

Finite fields in elliptic curve

I have an elliptic curve defined over finite field where $S_1=aP$ . Is it valid to say that $S_1P$ can also be computed. $P$ is the generator of the group. What my real question is that. Should '$a$' ...
1
vote
1answer
411 views

Discrete log problem with modulus prime

I am a bit confused on the hardness of the discrete logarithm problem. Does it become intractale only when it is mod n, where n is a large composite number (Like RSA key). What about if it is mod a ...
6
votes
1answer
211 views

What is the difference between Shor's algorithm for factoring and Shor's algorithm for logarithm

There is a paper from Peter W. Shor from 1994: http://www.csee.wvu.edu/~xinl/library/papers/comp/shor_focs1994.pdf "Algorithms for Quantum Computation: Discrete Logarithms and Factoring", and I have a ...

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