All Questions
2
votes
1answer
44 views
How to derive formulas for addition and multiplication in Jacobian coordinates
Is there a way to derive the formulas for point addition and multiplication on elliptic curves in Jacobian format by yourself? How could I have derived these formulas by myself?
1
vote
2answers
70 views
Many consecutive hashes to slow down brute force attack?
I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to prute force, without a noticable ...
-1
votes
1answer
63 views
Weak One Way Function
Show The function $mult(a,b)$ is weak one way if the Integer Factorization Assumption is true.
I am read the proof of this enunciated but I want know if I understand this in my way. The proof use the ...
1
vote
1answer
177 views
What does $(\mathbb{Z}_n^*)^2$ mean?
In a paper they write once, $(\mathbb{Z}_n^*)^2$. Is this the group of quadratic residues or is it something else?
Here the theorem:
Under the strong RSA assumption, given a modulus $n$, along with ...
0
votes
1answer
58 views
How to hash a structure that needs to include that hash's outcome?
so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
4
votes
1answer
94 views
Injecting salt into PyCrypto KDF - useful?
I have noted some sources indicate that when using a KDF like PBKDF2 (alternatively) some advocate injecting the salt at the time of execution - like this:
...
-1
votes
0answers
46 views
1
vote
1answer
61 views
Attacking AES/CCM with random IV
A cryptosystem is using AES-128 in CCM mode with random IV.
Suppose an attacker capable of:
asking the cryptosystem to encrypt a single plaintext as many times as he wants; and
asking the ...
2
votes
1answer
98 views
Are digital signatures secure for signing lots of small messages?
I need to sign the numbers from 1 to 1 billion (literally this, it's not an analogy) using a digital signature and then send these numbers in a particular order to someone. The message is not private ...
-1
votes
1answer
46 views
Solving a discrete logarithm using GDlog
I am trying to calculate an x, such that t = g^x mod p (I need to crack a weak elgamal encryption for university). I found gdlog, but I cant figure out how I can use the input to calculate my x. Here ...
6
votes
2answers
150 views
RSA leak bits to factor N
Suppose you randomly generate large primes p and q as in RSA, and then tell me N=pq but not p or q.
Then, you would like to actually let me factor N, except you should tell me as few bits of ...
-2
votes
0answers
53 views
What is a CBC Mac Scheme? How does knowing one block release other? [closed]
I guess CBC-MAC encryption relies on the previous block for encryption but how does knowing intermediate block cipher output make it insecure?
-3
votes
0answers
61 views
Show that for all integers n>2, n does not divide n^2+2 [closed]
I believe this solution can be solved by induction, I just don't know how to phrase it recursively.
For all n>2, n^2+2 mod n ≠ 0
Base case n=3
3^2 + 2 =11
11 mod 3 = 2 ≠ 0.
Show that
(n-1)^2 +2 ...
3
votes
1answer
99 views
Why SRP is not widely used?
SRP seems to be a very good password authentication protocol, compared to any other things used now. So why is there no popular implementations, or even no working secure implementations?
I tried to ...
-2
votes
3answers
102 views
how much is secure to encrypt a password using itself (as encryption key) for storing it on a unsecure media?
I want to store a password securely on a storage (suppose in a usual unencrypted file).
I use this password as AES key to encrypt itself (using AES-ECB) & then store it on the media (the password ...
0
votes
3answers
162 views
Implementing secret reconstruction in Shamir's Secret Sharing
I am trying to implement Shamir's secret sharing in C++.
I have got the generation of shares working.
However, I am very confused with the reconstruction of shares. I get the part on how three users ...
1
vote
2answers
90 views
Is there any strong enough pen-and-paper or mind cipher?
Some ciphers are talked about here, but I don't see an answer, are they strong enough, or are non-computer ciphers more or less just a toy and one should abandon using them for practical purposes?
0
votes
2answers
152 views
What's the difference between AES and earlier block ciphers?
Is there any difference except speed and key and block size from user's point of view?
Or does AES have something that ideal block cipher doesn't have?
-3
votes
0answers
37 views
DES chosen-plaintext attack in Windows [closed]
How do I do a DES chosen-plaintext attack in Windows?
1
vote
1answer
114 views
Indistinguishability attack example
I want solve the next exercise. The author defined the experiment for the cryptosystem $\Pi$, the adversary $A$ and the security parameter $n$ as follows
$\mathsf{PRIV_{EAV}}(\Pi,A,n)$
The ...
2
votes
2answers
119 views
How to derive two keys from one password
What is the best way to generate two independent symmetric keys from one user-entered password or passphrase?
Would using both scrypt and pbkdf2 achieve this?
-2
votes
0answers
34 views
session keys in an online e-voting system [closed]
I do not have much knowledge about cryptography or public and private keys, and your help will be much appreciated. I am totally a beginner, and no one from my university can help me.
I am trying to ...
-3
votes
0answers
82 views
Why is the basic (fixed-length) CBC MAC construction not a secure MAC when it is used on variable-sized messages? [closed]
Why is the basic (fi xed-length) CBC MAC construction not a secure MAC when it is used on variable-sized messages?
0
votes
3answers
276 views
Is AES really used for Top Secret stuff?
I've read almost everywhere that AES-256 can be used for Top Secret material (in the US). Is it really used or is it some kind of decoy to hide the more advanced algorithm they might use ?
0
votes
1answer
42 views
recommendation for steganography tool? [closed]
I am trying to find a good and referenced steganography tool to make some tests, it its freeware it would be great. Does anyone knows any recommended tool for this task? I have found some free ...
1
vote
1answer
67 views
Elliptic Curve is DH function or PKI?
can we reuse same ECC key on TLS for long terms or it must be used just once? (i mean can we use ECC like RSA?)
is there patent free ECC implementation ?
-1
votes
1answer
82 views
What length should the padding be when encrypting or signing with RSA?
Does it matter what length the padding is? If so - what length should it be?
(Another point: Should it be random?)
3
votes
1answer
144 views
CBC-MAC , fixed length, all blocks returned
CBC-MAC, with fixed length message.
Is it safe to return all ciphered blocks instead of the last?
My intuition says it is less secure, since is gives an attacker more information.
But how could one ...
2
votes
2answers
84 views
encrypt message with one digest 0-9 instead of 01-26
How much will the security of one-time pad decrease if I use one digit from 0-9 instead of 1-26?
for example plaintext = "blue" and ...
1
vote
1answer
100 views
Encrypt a single file, chunk-by-chunk, each chunk using different key (AES)
Encrypt a single file, chunk-by-chunk, each chunk using different key.
I am a security newbie (only took 2 security courses before)
But currently I am using this encryption method for my Android ...
6
votes
2answers
130 views
Have I understood pedersen commitment correctly?
I want to do a one-sided integer commitment scheme. I.e. the whole process must be non-interactive where I at one point first publicly reveal some data and then at a later time reveal the committed ...
0
votes
0answers
55 views
Perfect secrecy Proof
A symmetric cryptosystem have perfect secrecy $\iff$ for all
distribution over the messages space, $M$, and for all $m0$, $m1$ (messages) and any ciphertext $c$,
$$P(c|m0) = P(c|m1).$$
I got ...
-1
votes
2answers
55 views
Book Didactic Security Notions [closed]
I want study more about cryptography reading papers, but I have a problems to understand few concepts: security notions, random oracle model, IND-CCA, ... etc. I began study this concepts by internet: ...
3
votes
4answers
198 views
Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?
$H(s,r)=d$ is a function that hashes the secret string $s$ with a salt $r$, and returns a digest $d$.
$r$ may be arbitrarily chosen and each $r$ returns a different $d$.
For any $d$, $r$ is known from ...
1
vote
2answers
137 views
Is it worth applying a MAC on data in a HSM?
I'm building a basic HSM out of an Arduino, and am using the following scheme to store data:
Master symmetric key $k_m$ stored in firmware (secure bit set to prevent trivial extraction).
Secondary ...
1
vote
1answer
67 views
How to compare two datasets „anonymously”?
Ok, I hope this question makes some sense because I am not so sure how to word it any differently… Imagine the following situation:
There are 10 defined colors (blue, orange, yellow etc.)
There are ...
0
votes
0answers
35 views
Interesting game: decipher the following sequence [closed]
Decode the following sequence:
KROWE
MOHSI
HTDEY
OJNEI
The original cipher is printed in such matrix format
0
votes
3answers
86 views
Padding of Original Message in MD5
what should I do if my original message is greater than 64 bits? what is the process of padding in MD5?
As described in Internet Security: Cryptographic Principles, Algorithms and Protocols, page ...
0
votes
1answer
45 views
chaining rsa with ecies
In an answer to a previous question it was suggested that one way to protect your asymmetrically encrypted AES-256 keys, from say a solution to prime factorization, would be to chain asymmetric ...
5
votes
1answer
102 views
Proof that padded RSA is CPA-secure
I'm referring to page 383 of J. Katz and Y. Lindell's Introduction to Modern Cryptography. The book presents a padded RSA:
${\bf Key Generation:}$ same as Textbook RSA (given security parameter ...
1
vote
1answer
41 views
Adversary Two Stages
I am read this paragraph and I have a doubt.
"An adversary to PKC $\Pi$ is given by two probabilistic polynomial
time algorithms, $A = (A1; A2)$. In the first stage, the "find"
stage, the ...
2
votes
1answer
103 views
Why does key generation take an input $1^k$, and how do I represent it in practice?
In my lecture, the lecturer said:
Let $K$ be the key generation algorithm. Given a security parameter represented in unary, $1^k$, $K(1^k)$ will output a keypair $(pk; sk)$, known as the public ...
-1
votes
1answer
39 views
Sematically Secure McEliece
I am read the Lemma 2 (pp13) in the paper [1]. Here a make a question Why "for any $Hash_z$ and any $Gen$"? The author of paper reply
The reason why "for any $Hash_z$ and any $Gen$" is that if ...
3
votes
2answers
172 views
toy hash algorithm
I'm looking for a toy hash function, where the idea is to have high school students break (i.e. find a collision) a hash function by hand, in order to teach them how one way functions and hashing ...
0
votes
2answers
202 views
Custom crypto library in C
I will be making (in the near future) an app that will contain some pretty heavy crypto. As it is possible that my app will be ported to different devices (initially it will be iOs only, but Mac, ...
1
vote
1answer
81 views
Secure order preserving hash function
Is there a construction of an order preserving hash function that keeps the preimage property of a crypto hash function? By order preserving hash function (OPHF) i mean for $x<y$ then $OPHF(x) < ...
3
votes
2answers
109 views
what is the difference between Scrypt and PBKDF2
After reading these two resources I am wondering am I getting all the differences between Scrypt and PBKDF2 or am I missing something?
As far as I understood, the similarity is:
both are using ...
0
votes
1answer
48 views
Certificate == signed public key
For primes p and q used to create a keypair, I understand that the following operation is used to create a signature :-
M ^ d (mod N)
where d and N have their usual meanings and M is the message. In ...
0
votes
2answers
85 views
risk of attacker decrypting RSA ciphertext without public or private key
As I describe in my previous question I am trying to decide if it's worth it for me to use the Offline Private Key Protocol in creating some long term private archives, instead of just going with a ...
1
vote
0answers
37 views
Parallelizing AES GCM in BouncyCastle [migrated]
I'm using AES-GCM with the BouncyCastle provider in Java and it works fine. The NIST documentation seems to suggest that GCM is an algorithm that allows parallelization -- however, on looking at the ...
