All Questions
2
votes
1answer
111 views
Theoretical pi-based stream cipher
Let's pretend that all digits of pi are known and arbitrarily long sequences of digits are trivial to get. Further, some mathematician proves that there are no patterns in pi. We could create a stream ...
2
votes
1answer
69 views
Discrete log analog of ECM factoring algorithm?
Anecdotally, most factoring algorithms have a corresponding variant algorithm that can be used to attack the discrete log problem using similar ideas.
Is there an analog of the elliptic curve (ECM) ...
0
votes
0answers
47 views
How compute encrypt and decrypt runtime for agorithm [closed]
I programming RSA algorithm is the following two function in java language in my thesis
...
0
votes
0answers
30 views
How to create a public-key certificate for RSA Web of trust?
How to create a public-key certificate for RSA Web of trust?
I have (for exemple) two public / private key pair (obviously).
They all need to sign each other certificate.
How to create the ...
1
vote
1answer
97 views
How can encryption software accept password lengths which are not one of the AES key lengths?
AES comes with key sizes of 128, 192, and 256 bit.
But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit.
How is this ...
2
votes
2answers
178 views
Hashing passwords with a salt - why use different salt for everyone?
Given a database where we have usernames and passwords, we want to secure users' passwords by hashing them. We should not use only username and passwords in this hash, as someone having data from ...
2
votes
1answer
74 views
How much do we trust KEA1 Assumption?
Let $$(g,h=g^s,q)$$ be a tuple such that $g$ is a generator for a group $\mathbb{G}$ of ord $q$ and $s$ is uniformly random in $\mathbb{Z}_q$.
The KEA1 Assumption saies that for any adversary ...
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
2answers
66 views
GGM PRG construction: Why do we need to change keys all the time with underlying PRG
When constructing a PRF that has n bit input using the GGM PRG, why do we always have to recursively run the PRG using its previous output as a seed key n times. Instead, why don't we run the PRG n ...
3
votes
1answer
121 views
How to find an element of high-order in an RSA group?
Is this even possible? The RSA group is not cyclic, so usually you wouldn't find a generator for accessing all group elements.
What happens if you use the RSA group in a scenario where you want that ...
1
vote
1answer
57 views
What is the most secure way to let Alice “input” her private key, transfer it to the server and decrypt the message?
What is the most secure way to let Alice "input" her private key, transfer it to the server and decrypt the message? (Then destroy the private key on the server)
Every connection is using SSL.
...
-2
votes
1answer
62 views
Super-symmetric Stream cipher [closed]
What I want to know is, Is there a stream cipher with two modes Mode-1 (encrypt/decrypt) and Mode-2 (decrypt/encrypt)
i.e. it should be possible to encrypt and decrypt using Mode-1 and Mode-2 ...
-2
votes
1answer
89 views
What is the most paranoid way to exchange messages? [closed]
I'm looking for a way for Alice to send a message or a file to Bob in the most paranoid way possible (over the internet).
It can be asymmetric or symmetric. But According to some articles, AES ...
-2
votes
1answer
60 views
Cryptographic Primitive Method
Is there any cryptographic primitive bijective (one-to-one and onto) function for creating cryptographic tools like symmetric encryption/decryption, Hash code generator, MAC, HMAC and Random number ...
2
votes
3answers
62 views
Secure communication between multiple peers on a public channel
I am wondering how can I secure communications between multiple peers over a public channel, like an IRC channel. With two peers it is easy - they exchange their encryption keys and decrypt the secret ...
4
votes
3answers
145 views
What is a block cipher?
I have read about block ciphers, but I do not understand the topic completely.
Is a block cipher a way to send data or a way to encrypt data?
How is the data divided into multiply blocks before it ...
-2
votes
1answer
109 views
Same Size Crypto Algorithm?
I need to know there is any algorithm that crypts data in same size,
Any knowledge appriciated!
Thank you!
3
votes
1answer
114 views
Why does Rijndael with a 256-bit block require the bottom two rows to be shifted one more space than usual?
From Wikipedia:
For a 256-bit block, the first row is unchanged and the shifting for the second, third and fourth row is 1 byte, 3 bytes and 4 bytes respectively.
Why the change? Is there any ...
2
votes
1answer
90 views
Hashing a password with the password?
I was wondering if hashing a password with the password would be a good way of encrypting the password. So, the user must know his/her password to get the same result as the one in the database. Also, ...
4
votes
3answers
207 views
Initialize a PRNG with a password
Let's assume that we have a secure PRNG. Is it "safe" to initialize it with password, or seed based on a password like SHA256(password).
If yes, is it "safe" to generate as RSA or DSA key from it? If ...
4
votes
2answers
199 views
In the Paillier cryptosystem, is there a method to judge whether an encrypted number is less than 0 (without the private key)
Or, is there a cryptosystem that is both order-perserving and additive homomorphic?
2
votes
2answers
210 views
RSA private key format for Mega
I've been trying to reverse engineer Mega's (mega.co.nz) API calls. And stopped on the step where client needs to decrypt session id with provided RSA key. I can get key data, but I have no idea how ...
4
votes
1answer
81 views
How to generate a key using any m passwords out of total n?
My application requires an AES-256 key K for some secure operation. In order to avoid saving this key in application, I have implemented following scheme:
There ...
1
vote
1answer
84 views
Understanding padding oracles - is an attack plausible in my scenario?
I have a scheme that, long story short, uses AES in CBC mode to encrypt third-party credentials for user accounts with a password-derived key. It's been mentioned that the use of CBC mode is a ...
8
votes
1answer
204 views
Is Encrypt+HMAC stronger than AEAD?
There are a few posts that I've come across that seem to infer that using regular encryption and a MAC might be better than using the newer AEAD (ie: AES/GCM) modes.
...
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 ...
1
vote
1answer
73 views
Non-cryptographic hash function as MAC for stream ciphers
I understand that for a stream cipher to be useful, there must be a way to verify that the message was not tampered with (bits were flipped by an attacker).
So, instead of using some cryptographic ...
2
votes
2answers
97 views
Does it take brute force to find a pair of plaintext and ciphertext that each follow a certain condition, given an AES encryption key?
Suppose that I have an AES key $K$, and I'm instructed to find a plaintext such that the first 32 bits of the plaintext are some string of bits $S_1$, and the last 32 bits of the ciphertext once the ...
2
votes
1answer
52 views
Discrete logs on elliptic curve with embedding degree 3 with the 'MOV' attack
The curve $E(\mathbb{F}_{47}):y^2=x^3+x+38$ has order $61$ and $61|47^3-1$ so the embedding degree of $E$ is $3$ and therefore the MOV attack, presumably using some sort of distortion map and a ...
1
vote
1answer
54 views
Two files encrypted with related data versus one file
I have some code that takes a list of credit-card numbers, splits the number into two chunks, one chunk is 8 characters long, the other chunk is the remainder.
Each series of chunks is saved into ...
0
votes
1answer
42 views
Reference papers for protocol proving [closed]
I am working on few cloud cryptography protocols. i am new to protocol design, definitions and proving .
With some preliminary research i understand that there are two models of security proofs
one ...
4
votes
5answers
332 views
Any efficient text-based steganographic schemes?
While there are sophisticated and efficient steganographic schemes with images as cover available, I am yet ignorant of the existence of any fairly efficient and secure schemes with texts as cover. ...
4
votes
1answer
69 views
Security for IV in AES-GCM mode
I'd like to use AES-GCM instead of HMAC for authentication and privacy in a token used in a web application, but I'm unsure how to securely tag each token with an IV. Is it safe for me to prepend the ...
3
votes
2answers
140 views
Modulus for elliptic curve point multiplication
I want to implement a point multiplication ($k \cdot P$) operation on FPGA. I have a BN curve $y^2=x^3+2$, and a scalar value $k$. The $x$ and $y$ coordinates of point $P$ are of 256 bits. In the ...
3
votes
1answer
72 views
Why work in a subgroup QR(n) of an RSA group $Z^*_n$?
I sometimes read in papers that a (sub-)group generator $g$ is taken from $\mathrm{QR}(n)$ instead of $\mathbb{Z}^*_n$, where $n = p \cdot q$ and $p$ and $q$ are prime. Is there a reason for this? ...
0
votes
0answers
47 views
How compared encryption algorithm in terms of efficiency
I doing to compare two algorithm cryptography. first algorithm is RSA cryptography and second algorithm is El Gamal elliptic curve cryptography. now I want a way to compare between two algorithm by ...
-2
votes
1answer
98 views
What encryption is this? [closed]
uwwmXzKSP0M7DHBHns3v2CtNZh0TOicb
uwwmXH6KGgVLjpnoWCk9I2A+
uwwmcv7JoND9WE6xwaXdN6fLXaecRPqf+m6WmqE
uwAm5NXph0c9hkFK
are originally:
001bboc@explorer.csc.com
001bocaj@gmail.com
...
3
votes
1answer
86 views
Any implication of a Yale result to security of quantum cryptology?
Quantum key distribution depends, if I don't err, on (irreversible) damages done by MITM's measurements on qbits. Now news.yale.edu/2013/01/11/new-qubit-control-bodes-well-future-quantum-computing ...
2
votes
1answer
169 views
How can I calculate the time complexity of modular arithmetic?
I'm doing modular arithmetic in a Java program, and I want to calculate the time complexity of the individual operations.
$$ c= a · b \bmod n $$
$$ m = a^{-1} · b \bmod n $$
How do I get an ...
1
vote
1answer
64 views
How does this Cesar Cipher work?
Suppose I have this cryptogram: http://pastebin.com/QpfRMBg1
Clearly it's a Ceasar Cipher which decrypts to: http://pastebin.com/r50heZuU
with a simple shift of 10... OKay, no big deal. Let's take a ...
3
votes
2answers
117 views
How does using salt reduce rainbow table attack?
I could create a rainbow table for a particular salt value and still create a successful attack similar to one without salt value.
1
vote
1answer
101 views
Finding a collision for a hash function
I'm trying to find a collision for the following (modified) Merkle-Damgard hash function.
Suppose we already have a hash function $h : \mathbb{Z}_2^{2·n} \to \mathbb{Z}_2^n$ for fixed length bit ...
3
votes
0answers
96 views
CBC with fixed IV but changing data [duplicate]
Possible Duplicate:
Using CBC with fixed IV
I am using AES in CBC mode.
For some reasons I have some issues for transmiting the IV. So I am using a fixed IV.
If the first 128bits of the ...
1
vote
1answer
236 views
AES CBC mode or AES CTR mode recommended?
what's benefits and disadvantages of CBC vs CTR ? which one is more secure ?
2
votes
2answers
136 views
Which categories of cipher are semantically secure under a chosen-plaintext attack?
I am trying to get my head around the circumstances under which a cipher is (or is not) semantically secure under a chosen-plaintext attack.
I can't seem to find a good reference explaining this.
I ...
2
votes
2answers
118 views
Is it safe to use RSA as a proof-of-work system?
Suppose I devised the following challenge-response proof-of-work system:
A server generates a 2048-bit RSA modulus, and uses the "public" exponent (usually 65537) to sign a random nonce a fixed ...
2
votes
1answer
150 views
estimate of time required to crack sha512crypt password with JtR + OpenCL
OK, I have a shadow file with a password that I know, it is 4 letters followed by two numbers. Using John The Ripper with OpenCL support, on a laptop with AMD Radeon Mobility graphics, how long would ...
3
votes
2answers
713 views
Many time pad attack
I've already sent my correct solution to a programming question on an online class:
Let us see what goes wrong when a stream cipher key is used more than once. Below are eleven hex-encoded ...
0
votes
0answers
40 views
elgamal based decryption mixnet
Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also.
...
6
votes
1answer
369 views
Difference between Rijndael 128 / 256 blocksize implementations? (and impact of block size in general)
Can anyone shed some light onto the advantages/disadvantages of using Rijndael with 256-bit block size, as opposed to the 128-bit (AES) implementation? (please note: I'm not referring to key-size ...
