All Questions
8
votes
0answers
135 views
What changed in PKCS#1 v2.2, and why?
PKCS#1 is one of the most used (de-facto) standard for real-world use of RSA.
That's for good reasons: PKCS#1 is well thought, versatile, understandable, has been relatively stable for over two ...
5
votes
0answers
144 views
Prove that textbook RSA is susceptible to a chosen ciphertext attack
Given a ciphertext $y$, describe how to choose a ciphertext $\hat{y} \neq y$, such that knowledge of the plaintext $\hat{x}=d_K(\hat{y})$ allows $x=d_k(y)$ to be computed.
So I use the fact that the ...
5
votes
0answers
58 views
MD4 First preimage - state of the art
What's the state of the attack to get the first preimage on MD4?
Is it still this http://www.di.ens.fr/~leurent/files/MD4_FSE08.pdf in 2^102 ?
5
votes
0answers
39 views
Efficient decoding of irreducible binary Goppa codes and the role of matrix P in McEliece cryptosystem
If we assume that the support for an irreducible binary Goppa code $\gamma_1, ..., \gamma_n$ is publicly known, when is it possible to efficiently decode the code? I know it's possible if one knows ...
4
votes
0answers
87 views
Pseudo preimage for a hash made from a cipher
Consider the Miyaguchi–Preneel construction:
$H_0 = E(0,m_0) \oplus m_0$ (0 here means a vector filled with zeros)
$H_1 = E(H_0,m_1) \oplus H_0 \oplus m_1$
where $E(K,M)$ is a block cipher (for ...
3
votes
0answers
83 views
How can scrypt be improved to counter GPU mining
I know scrypt was designed to lessen the GPU/ASIC advantage.
We now have litecoin as a real-world example of this. However, it hasn't worked out perfectly. Most coins are mined by GPUs, although the ...
3
votes
0answers
101 views
Questions on rank-attacks in Multivariate Cryptography
While reading this article on rank attacks on STS (a public-key scheme based on Multivariate Quadratic (MQ) equations), I stumbled upon some claims that I've also seen in other presentations on ...
3
votes
0answers
125 views
Finding where I am in a linear recurrence relation
Suppose I have a linear recurrence relation
$$a(n) = c_1 a(n-1) + \dots + c_k a(n-k) + d,$$
where the constants $c_1,\dots,c_k,d$ are given and the initial values $a(0),\dots,a(k-1)$ are given as ...
3
votes
0answers
216 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. ...
3
votes
0answers
341 views
Elliptic curve cryptography related key attacks
This question is an extension of Families of public/private keys in elliptic curve cryptography
As described above, bitcoin "type 2" deterministic wallets use a root private/public key pair, where ...
2
votes
0answers
97 views
LT codes with Homomorphic hashing
I have been working on a project implementing LT codes with Homomorphic hashing (inspired from http://blog.notdot.net/2012/08/Damn-Cool-Algorithms-Homomorphic-Hashing and ...
2
votes
0answers
114 views
Correct way to truncate data to a range
2 hours ago I thought I had this figured out, but now I am doubting myself and want someone to validate my algorithm.
I want to take a stream of k trusted random ...
2
votes
0answers
68 views
How can I prove that this encryption scheme from a random oracle is secure?
I am reading this example:
A random oracle is an ideal object.
What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
2
votes
0answers
45 views
Relaxed trust criterion for mental poker server?
I've read a lot about protocols for mental poker without a trusted server, but I'm interested in the possibility of a faster, more practical protocol that relaxes that criterion a bit and "trusts" a ...
2
votes
0answers
98 views
Single-purpose symmetric encryption scheme for single files
I'm writing a simple password manager program that will encrypt/decrypt a single file (it's size will most likely stay under a few K). This is my initial file format design:
...
2
votes
0answers
65 views
State of the art in zero knowledge proof compilers?
What is the current state of the art zero knowledge proof compiler ? I need one that can minimally handle double exponentiation by a known value E.g.
$$Pok\{(\alpha):h=g^{\alpha^b}\} $$
where b, ...
2
votes
0answers
78 views
Are there any secure commutative ciphers?
This answer lists two commutative cipher algorithms - Pohlig-Hellman and SRA. However, they don't appear to be too secure.
My question is, here there any commutative ciphers out there that are secure ...
2
votes
0answers
38 views
Unique GCM/CCM initial counters without recipient side message counters
I am implementing the encryption layer for a communication protocol. The bulk encryption method used is either AES-CCM or AES-GCM. Due to implementation details, encryption of packets is usually, but ...
2
votes
0answers
57 views
Implementing PKCS#7 Padding on a Stream of Unknown Length?
I have a fairly simple Python program using PyCrypto to use AES+CBC to encrypt a stream of input. In order to adhere to the 16-byte input size multiple, I've implemented PKCS#7 by hand. (While I know ...
2
votes
0answers
69 views
Why does the SRP6 calculation of B included a multiplier k = 3?
In SRP6 $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$?
(In SRP 6b, this value $3$ is replaced by $k = H(N,g)$, but this question is about SRP 6.)
2
votes
0answers
55 views
How do you construct a practical full-domain hash function?
I am looking for practical constructions for Full Domain Hash.
I have read Random Oracles are Practical by M. Bellare and P. Rogaway, the construction suggested on page 8, under "Uniformity: a ...
2
votes
0answers
123 views
Creating colliding x509 certificates: Crafting RSA moduli step
I am trying to generate 2 x509 certificates with the same signature but different values in the common name field, based on md5 collisions, as it was specified in this paper (page 7).
Now I have ...
2
votes
0answers
46 views
Encrypting or HMACing password digests
Assuming I'm using bcrypt to digest passwords, is any additional security gained by either encrypting or HMACing the resulting digests? By requiring a key to compare password hashes, I would expect ...
2
votes
0answers
108 views
Odds of false error detection in a randomness test using the chi-squared test?
Common Criteria classifies the requirements for true Random Number Generators, and specifies how these should be tested against failures (these can occur accidentally, or following deliberate attack, ...
2
votes
0answers
61 views
Differential Cryptanalysis of FEAL-4
I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall.
Basically I attacked the final round first (K3) using the differential characteristic of ...
2
votes
0answers
97 views
Transforming simplest protocol into a Sigma-protocol
I have some questions from previous years exams, I hope you could help me with them. :)
Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...
2
votes
0answers
147 views
Does Keccak have an eTCR mode?
On page 7 of NIST's views on SHA-3's security requirements and Evaluation of attacks, I see that, at least at this point, NIST planned on offering SHA-3 having eTCR security (defined on page 3):
...
2
votes
0answers
101 views
Ring Signature - paper/code difference in trying to solve inverse trap door function?
there is a paper on ring signatures and a python implementation of it here.
The Step 4 in the paper describes $y_s = v =C_k,_v(y_1, y_2, ... y_r)$ for all $1 \leq i \leq r$ where $i \neq s$. The ...
2
votes
0answers
163 views
Is there a practical zero-knowledge proof for this special discrete log equation?
We have a multiplicative cyclic group $G$ with generators $g$ and $h$, as in El Gamal. Assume $G$ is a subgroup of $(\mathbb{Z}/n\mathbb{Z})^*$. There are two parties, Alice and Bob:
Alice knows: ...
2
votes
0answers
48 views
Are there any systems like SDSI / SPKI that are currently being developed?
SPKI / SDSI look interesting but appear to have fizzled out and died. Are there any modern competitors?
2
votes
0answers
74 views
How to properly format a PGP Message Block?
As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
2
votes
0answers
133 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 $p$ ...
2
votes
0answers
113 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 ...
2
votes
0answers
349 views
Secp256k1 ECDSA test vectors
I`m currently implementing an ECDSA library based on curves like secp256k1. I would like to test it using some test vectors, like ...
1
vote
0answers
51 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 a Koblitz curve.
I've read many papers that show that computing some functions, like $f(P)=3P$ can be computed faster than the standard way. ...
1
vote
0answers
68 views
Question about proof of knowledge defintion?
I am just reading the "soundness"-definition for proofs of knowledge by Bellare / Goldreich. A proof of knowledge is a proof between a prover $P$ and a verifier $V$. $P$ convinces $V$ to know a secret ...
1
vote
0answers
63 views
Is OAEP reversible?
Given nothing more than some integer $m =$ OAEP($M$), is it possible to recover the original plaintext $M$? In other words, without being given the hash functions or the random string used for ...
1
vote
0answers
57 views
Algorithm digipass-like
I'm pretty sure there are famous algorithms for my problem, but I don't have enough knowledge in this field, so I need your lights.
Here si the problem :
Alice sends key X to Bob.
Bob has an ...
1
vote
0answers
55 views
PKC McEliece + $S$ + $P$
I am trying implement the McEliece crytosystem in SAGE. My question is How I will be able to choose the appropriate matrix $S$ and $P$?. I ask this because when I trying obtain the vector $\hat{m}=mS$ ...
1
vote
0answers
52 views
Perfect secrecy and change of plaintext probability distributions
How to prove that if a cryptosystem has perfect secrecy for a given plaintext probability distribution then it will have perfect secrecy for all other possible plaintext probability distributions?
Do ...
1
vote
0answers
68 views
Known-plaintext attack on Blowfish in ECB mode
The protection scheme I faced recently seems so weak nowadays that a simple exhaustive key search would be enough to recover the user key in an acceptable amount of time (it's OK, since almost no ...
1
vote
0answers
48 views
Predicate Encryption supporting disjunctions
I am not sure if I missed some subtlety in the definition of Attribute Hiding found in this paper on Predicate Encryption, but isn't it possible to construct a scheme for Predicate Encryption ...
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 ...
1
vote
0answers
82 views
One-time pad and perfect secrecy properties
I have a homework problem:
Explain how to find $m_{0}$ and $c$ such that $P[c=c': k \leftarrow K, c' \leftarrow E(k, m_{0})] > 0$
where P is probability and k is chosen uniformly.
I do not know ...
1
vote
0answers
64 views
How to represent point-at-infinity in affine coordinate
In projective coordinates point-at-infinity can be identified with z=0. How to identify the point-at-infinity in affine coordinate.
Whether x=0 and y=0 can be considered as point-at-infinity in ...
1
vote
0answers
53 views
Prevent/minimize replay attacks in public message board
Assume we have a public message board where anyone can send a message to. If plain messages are used, anyone can impersonate anyone. The goal is to disallow impersonations. We can use public key ...
1
vote
0answers
37 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 ...
1
vote
0answers
80 views
Are hash trees an alternative, quantum-resistant signature scheme which can replace RSA?
Can hash trees can provide quantum resistant signatures to replace RSA for signing securely? What is the key size and how many times can we use same key?
1
vote
0answers
84 views
Determining the algorithm used to generate a digital signature
I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature.
From the signed string, is it possible to find out what ...
1
vote
0answers
48 views
P-Complete hashes, hashing to a larger set
Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits).
Also, hash functions that are P-complete have no known parallel algorithm; they must be computed ...
