All Questions
0
votes
1answer
58 views
What is a fair exchange scheme?
The Wikipedia entry Fair exchange has only two lines, and the only paper I can find describing such a protocol is extremely complicated.
Is this a new field in cryptology or can someone give an ...
0
votes
1answer
59 views
Encrypting a broadcast channel
We're building a data service that is expected to go out through a single "fat pipe" channel. The design requirement says that the data in the channel must be protected by authentication and ...
3
votes
1answer
127 views
Using an MD5 hash as a password
Suppose Alice is using a password prompt that only accepts up to 32 characters for any particular password.
Memorization of long strings of random characters is not one of Alice's strengths, so she ...
11
votes
2answers
847 views
Why is H(k||x) not a secure MAC construction?
If H(m) is a secure hash function, can't we implement a MAC using H(k||m)?
However, it seems the more widely used MACs, such as NMAC and HMAC (both originally defined in Keying hash functions for ...
1
vote
2answers
81 views
CSPRNG in JavaScript using Audio and Video
I ported GnuPG to Javascript using Emscripten (not released yet).
Now I need a good replacement for /dev/random//dev/urandom.
...
2
votes
1answer
69 views
Why is the discrete log problem easy when the exponent comes from a binomial distribution?
I read in http://epubs.surrey.ac.uk/7219/2/esorics06.pdf that in exponential El Gamal the discrete log problem for recovering $m$ from $g^m$ can be made tractable when $m$ is drawn from a binomial ...
3
votes
1answer
95 views
Trying to better understand the failure of the Index Calculus for ECDLP
So I'm going to give you guys my understanding and then if you would be so kind as to tell me where I'm off the mark (hopefully I'm not completely wrong).
So basically the index calculus for the ...
20
votes
10answers
2k views
Now that quantum computers have been out for a while, has RSA been cracked?
D-wave systems has released a commercially viable quantum computer. This means; in theory, that all asymmetric encryption algorithms, such as RSA are now useless, due to the speed at which quantum ...
0
votes
2answers
75 views
random number generator 10-side dice alternative
A lot of sites like this one Here, refer to 10-side dice to generate random number for otp. I was thinking about new ways to generate random numbers,letters and passwords. here what I got.
to ...
2
votes
4answers
173 views
Increased CRC collision probability when adding bits to input message
The Scenario
I have a message string I need to transport over a wireless network that may be unreliable. This message string is about 100 bits long, and is packaged with an 8-bit CRC. When the ...
1
vote
2answers
85 views
Why is the following RSA PRNG cryptographically secure?
One requirement states that the generator has to withstand the next-bit test.
Consider the following PRNG, where we calculate next output $x_i$ via the formula
$x_i = x_{i-1}^ e\mod n$.
I can see ...
1
vote
3answers
672 views
Does encrypting twice using the same block cipher produce a security weakness?
If I use the output of a cipher, for example a block cipher such as AES and encrypt it again with the same algorithm, I read that this introduces weaknesses into the overall security of the system.
...
0
votes
1answer
105 views
Designing a security system from scratch with a custom protocol, suggestions needed
For the reasons I cannot go into details, I need to design my own protocol and overall security system which will be used to establish secure data exchange between various devices (most notably ...
4
votes
1answer
148 views
Why xor the message into the state for sponge hashes?
Sponge hashes like Keccak(SHA-3) and CubeHash, xor a message block into part of the internal state. Why use a reversible operation like xor for that, instead of replacing that part of the state with ...
6
votes
3answers
205 views
What kind of adversary is the cloud?
I just started some work on computation over encrypted data in the cloud. We're still in the early planning stages, and to really understand the kind of security we can offer I need to determine what ...
-3
votes
1answer
68 views
Can someone help with the following hashes? [closed]
Here are a couple of hashes. I feel it should be easy (simple base conversions?) to decode them but I haven't succeeded so far. Can someone help?
...
-5
votes
0answers
58 views
Crypting text cheating wife on iphone [closed]
Wife received text looks like Chinese with boxes
I am new to cheating with adware and crypting
And embedding can I buy a service or app and cut and paste or copy these texts and they are
Sent back ...
1
vote
2answers
97 views
Combining LFSRs for Stream Ciphers: Why do we need high non-linearity?
Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ...
-3
votes
0answers
86 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
1answer
58 views
Does SRP reduce to DH key echange when shared password is not secret?
I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later.
I ...
6
votes
2answers
165 views
Finding hash almost-collisions
A few months ago, XKCD posted a challenge to find a plaintext which hashed (using Skein 1024 1024) to a specified value. Inputs were scored based on the hamming distance between the hash of the ...
4
votes
2answers
102 views
How to do a literature search
How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ...
-1
votes
1answer
70 views
Cryptography based upon neural networks [closed]
I would like learn about use neural networks in cryptography. Is there any research literature on this subject? What should I do to learn about the subject?
I am taking short course in neural ...
0
votes
1answer
41 views
Is the DES algorithm in OPENSSL random?
Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext
...
1
vote
1answer
78 views
Security of Salsa20 with some known plaintext?
Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known?
Assume that a different IV and Key are generated before each file is ...
1
vote
1answer
185 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 ...
2
votes
2answers
105 views
Does knowledge of original file size provide a cryptographic weakness?
I'm encrypting files using an AES-256 CBC cipher and an SHA-256 HMAC every 64KB in the file. Since AES CBC needs an amount of input bytes to be divisible by 16, I use PKCS#7 padding to bring the ...
1
vote
1answer
87 views
Given a certain entrophy per character, how long should a passphrase be to guarantee key strength?
Given an entrophy of 1.5 bits per character, how long does a passphrase have the be to guarantee a key strength of a 128 bit random key?
Assuming an alphabet of 26, one character takes log2(26)=4.7 ...
2
votes
1answer
94 views
Winzip AES256 vs PGP
If I use the AES256 option in Winzip to encrypt a file, is it any less safe or less secure than using pgp encryption?
0
votes
2answers
211 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, ...
0
votes
0answers
27 views
Decrypting TLS in Wireshark when using DHE_RSA ciphersuites [migrated]
How can I decrypt TLS messages when an ephemeral Diffie-Hellman ciphersuite is used? I am able to expose the premaster secret and master secret from the SSL Client. Using that, how to decrypt the ...
2
votes
2answers
87 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 ...
3
votes
1answer
148 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
1answer
45 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?
2
votes
1answer
110 views
Recommended way of adding a pepper/secret key to password before hashing?
There have been several questions regarding password hashing here and on Security.SE.
A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ...
6
votes
2answers
159 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 ...
-1
votes
1answer
84 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?)
-1
votes
1answer
64 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 ...
3
votes
2answers
184 views
AES - plaintext is smaller 128 bit - how to expaned?
we are currently developing a little AES implementation in a crypto-course at university.
As far as I know, AES uses 128 bit blocklength, so all data that will be encrypted will get split up into ...
1
vote
2answers
71 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 ...
4
votes
1answer
96 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:
...
0
votes
1answer
59 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
0answers
63 views
RSA Encryption Sckeme [closed]
Can anyone help me with this question?
A and B want to exchange encrypted messages; specifically, B wants to send a message M
written in binary format to A, which needs to be encrypted. They agree on ...
3
votes
3answers
926 views
What should be the size of a Diffie-Hellman private key?
I'm implementing the SRP-6 protocol, which relies on discrete logarithms for it's security (essentially Diffie-Hellman).
The RFC documents state:
The private values $a$ and $b$ SHOULD be at least ...
2
votes
1answer
104 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 ...
0
votes
3answers
172 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
votes
0answers
47 views
1
vote
1answer
65 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 ...
7
votes
4answers
429 views
How do you find a cheater in Shamir Secret Sharing?
If there are 4 people involved, and every two of them should be able to know the secret (the polynomial is just a line) and you are given f(x) and x for each of those people, and you know one of them ...
1
vote
1answer
120 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 ...
