3
votes
1answer
121 views
Alternatives to HMAC + CBC?
I'm looking at using HMAC + CBC. The combination looks like this:
ciphertext = AES256(text, k1)
data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext
Where:
...
2
votes
1answer
108 views
How does OAEP improve the security of RSA?
The heart of OAEP algorithm used for RSA encryption are the cryptographic hash functions $H$ and $G$.
Does everybody (so also an adversary) know these functions?
If YES: How does it help the ...
3
votes
1answer
66 views
When truncating an AES MAC value by “w” , how do I justify that “w” is still negligible?
I'm taking an online class on cryptography at corsera.org / Stanford, and the professor is explaining that it's OK to truncate an AES MAC to $w$ bits as long as $1/2^w$ is still negligible (say $w ...
16
votes
1answer
358 views
Selective format-compliant JPEG encryption?
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping ...
1
vote
1answer
112 views
Is this a sensible cryptographic protocol intending to reduce the impact of compromised security?
I'm in the process of designing a cryptographic protocol which will reduce the impact an attacker will have if they gained root access to a server storing data.
The basic crux of it is that keys ...
0
votes
2answers
102 views
Generate fixed length cipher text from arbitrary length plaintext
Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
2
votes
2answers
128 views
Generating IV in TLS 1.2
I'm writing a TLS 1.2 implementation (in C#) using a custom protocol.
My question is how to generate the IV attached to each message, I don't want to use RandonNumberGenerator because I've heard it ...
1
vote
2answers
145 views
Help me describe/identify this challenge-response protocol/algorithm?
My area of expertise is reverse engineering, specifically embedded systems. I do attack cryptographic systems, but this largely involves key recovery or exploiting the implementation.
I was asked to ...
0
votes
2answers
203 views
SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?
Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
3
votes
1answer
169 views
Understanding Feldman's VSS with a simple example
I'm trying to understand Feldman's VSS Scheme. The basic idea of that scheme is that one uses Shamir secret sharing to share a secret and commitments of the coefficients of the polynomial to allow the ...
1
vote
2answers
78 views
Is Functional Encryption about Access Control over encrypted data alone?
Informally, In functional encryption system , a decryption key allows a user to
learn a function of the encrypted data. But all i see is that the function acts as an access control over the data.
...
1
vote
2answers
129 views
True random numbers generated by sensors
Is using sensor raw data a good way of generating true random numbers? I mean using an IPhone's gyro/accelerometer raw output as a base for generating an array of true random numbers.
2
votes
1answer
1k views
How to solve MixColumns
I can't really understand MixColumns in Advanced Encryption Standard, can anyone help me how to do this?
I found some topic in the internet about MixColumns, but I still have a lot of question to ...
0
votes
0answers
33 views
calculating beta for elgamal elliptic curves [duplicate]
Suppose we use elgamal elliptic curves for secure communication. Bob selects a prime $p$, an elliptic curve $E$, a point $\alpha$ on $E \pmod p$, and a secret integer $f$. Suppose that Bob has ...
1
vote
3answers
465 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 ?
2
votes
1answer
261 views
Partial collisions for md5
Let $h$ be a bitstring and let $P(h, n)$ be the n-bit prefix of $h$. A partial collision of length $n$, for a hash function $H$ is a pair $(x,y)$, such that $P(H(x),n)=P(H(y),n)$.
What is known about ...
0
votes
1answer
28 views
PKCS#11: Which CKK_types are supported by CKM_PKCS5_PBKD2?
On Solaris there's a function pkcs11_PasswdToKey() which is a wrapper of C_GenerateKey(). I made a simple test and it turned out ...
3
votes
2answers
252 views
Is there a way to do fair exchange between two parties who don't trust each other?
Let's suppose we have an Alice who knows a secret key A, and Bob who knows key B. Using their own keys, they each encrypt a message (Alice encrypts $m_A$, Bob encrypts $m_B$) with their own key, and ...
0
votes
1answer
65 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
63 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
175 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
891 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 ...
2
votes
1answer
81 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
102 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 ...
1
vote
2answers
101 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
210 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
96 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
740 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
119 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
150 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
288 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
70 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?
...
1
vote
2answers
117 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 ...
6
votes
2answers
190 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 ...
5
votes
2answers
125 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
76 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
51 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
89 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
200 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
113 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
93 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
127 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
243 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, ...
2
votes
2answers
97 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
177 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
51 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
122 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
183 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
92 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?)
