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1500 questions
22
votes
6 answers
Why are PRNG in programming languages not cryptographically secure by default?
In most programming languages, there is a module or function in the stdlib for creating random output like random.random() in Python.
Because those functions use a normal PRNG that is not cryptographically secure, over all the years those generators…
Aliquis
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22
votes
6 answers
Types of Cryptography for a 4-8 bit microcontroller
This is more of a research question.
I was wondering what types of crypto algorithms would work best on a small 4-8 bit micro controller. I recently read a paper called Security Considerations for 802.15.4 Networks and was wondering if anyone out…
Jim
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22
votes
2 answers
Deriving Keys for Symmetric Encryption and Authentication
So here's the concept. Rather than storing 2 keys and using a random IV, which presents its own problems (key rotation, ensuring no key is used in more than 2^32 cycles, sharing the keys, etc), is it OK to derive the cipher key, authentication key…
ircmaxell
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22
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5 answers
Using CBC with a fixed IV and a random first plaintext block
What if, instead of using CBC mode in the normal way with a random IV, I used this approach:
Use a fixed IV (like a block of 0's).
Before encrypting, generate a random block and prepend it to the plaintext.
After decrypting, ignore the first…
danieltorres
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22
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3 answers
Why is Curve25519 in the GPG “expert” options?
The only way to access the Curve25519 curve in GPG is through gpg --expert --full-gen-key.
From my knowledge, Curve25519 is one of the most secure (and fast) elliptic curves in cryptography. So why is RSA fine, but Curve25519 is considered a risk…
Richard R. Matthews
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22
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1 answer
Are there any well-known examples of SHA-256 collisions?
The popularity of SHA-256 as a hashing algorithm, along with the fact that it has 2256 buckets to choose from leads me to believe that collisions do exist but are quite rare.
Are there any well-documented SHA-256 collisions? Or any well-known…
Ari Sweedler
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22
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5 answers
How come hash salt doesn't make a hash ineffective?
I am not a cryptography expert. I watched this video regarding hashing and salting as part of the course User Authentication With Express and Mongo in teamtreehouse.com.
I understand from the video that a hash is a representation of a password…
user41937
22
votes
3 answers
Is AES in CBC mode secure if a known and/or fixed IV is used?
I have a need to encrypt credentials for a third-party app used by a secured internal app. Over on ITSec.SE, I was helpfully shown a scheme to encrypt the third-party credentials based on a hash of the credentials for the internal app.
I picked AES…
KeithS
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22
votes
1 answer
What size of initialization vector (IV) is needed for AES encryption?
What size of initialization vector (IV) is needed for AES encryption?
I am using either CBC or CFB modes.
Knowing that AES is a sysmmetrical block-cipher algorithm with a 128-bit block size, I think the answer for IV is still 16 bytes or 128 bits…
wei3923
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22
votes
4 answers
How long would it take to brute force an AES-128 key?
How long would it take to crack a AES-128 key using the most advanced technology currently available? The hardware can be anything, be it a high-performance CPU, GPU or even FPGA?
Joy
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22
votes
1 answer
What is the maximum size of the plaintext message for RSA OAEP?
OAEP is an important technique used to strengthen RSA. However, using OAEP
(or any technique that adds randomness) reduces the size of plaintexts that can be encrypted.
Assume for instance that OAEP is using a 160-bit seed and a hash function that…
Sarkar
22
votes
2 answers
What are the main weaknesses of a Playfair cipher, if any?
What are the main weaknesses of a Playfair cipher, if any?
I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other problems with it?
Arlen Beiler
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22
votes
1 answer
How many qubits are required to break RSA 2048 or 4096 with a universal quantum computer?
So in the news this week, IBM have created a universal quantum computer with 5 fully functional qubits. Logic and Moore's law dictates they will be able to scale this up to a lot more qubits within a few years. With Shor's algorithm, elliptic curve…
ite
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22
votes
1 answer
Mapping points between elliptic curves and the integers
My primary question is:
Is there an easy way to create a bijective mapping from points on an elliptic curve E (over a finite field) to the integers (desirably to $\mathbb{Z}^*_q$ where $q$ is the order of E)?
To phrase it a second way, given a…
PulpSpy
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22
votes
7 answers
Current mathematics theory used in cryptography/coding theory
What are the mainstream techniques borrowed from algebraic geometry (or some other branch of mathematics) which are currently used in cryptography/coding theory? I've only heard about a small subset of elliptic curves and hermitian curves. I've also…
Vicfred
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