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1500 questions
52
votes
6 answers
Who uses Dual_EC_DRBG?
Recent news articles have suggested that the NSA may be involved in trying to influence the cryptography in public standards or commercially deployed software, to enable the NSA to decrypt the encrypted traffic. For example, see this article in the…
D.W.
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51
votes
1 answer
What are SNARKs?
What does it mean and what is it used for, I have been hearing this term a lot lately.
From the context I've heard it talked about it seems to be connected with zero knowledge?
wi1
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51
votes
5 answers
How to find modulus from a RSA public key?
I am studying the RSA cryptosystem. The public key consists of $(n, e)$, the modulus (product of two large primes), and the encryption exponent. I want to separate the modulus $n$ and exponent $e$. A typical public key is expressed in base64, and is…
user3001408
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50
votes
2 answers
Why is SHA-1 considered broken?
Is there a known pair of distinct bit strings (A,B) such that SHA-1(A) == SHA-1(B)?
If the answer is no, then how can SHA-1 be considered broken?
Andrew Tomazos
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50
votes
3 answers
What are the benefits of the two permutation tables in DES?
Why do we use a permutation table in the first step of DES algorithm and one at the end of the algorithm?
Am1rr3zA
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49
votes
8 answers
Is there a simple hash function that one can compute without a computer?
I am looking for a hash function that is computable by hand (in reasonable time). The function should be at least a little bit secure: There should be no trivial way to find a collision (by hand). For instance, a simple cross-sum is not meeting this…
FUZxxl
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49
votes
2 answers
Differences between the terms "pre-master secret", "master secret", "private key", and "shared secret"?
Both crypto.SE and security.SE have excellent Q&As about how TLS generates session keys (I have linked some at the bottom).
In reading these threads I'm having troubles with terminology since the following terms seem to be used with overlapping…
Mike Ounsworth
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49
votes
1 answer
AES256-GCM - can someone explain how to use it securely (ruby)
I am looking into using AES256-GCM for encrypting some database fields. I know that for AES256-CBC, I need to generate a new IV for each encrypt, but I can use the same key. The IV can be openly stored alongside the ciphertext (ie, it can be…
breakingbreadmuffins
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48
votes
2 answers
How is the Swiss post e-voting system supposed to work, and how was it wrong?
I read that the Swiss post had an e-voting solution developed, made it possible to obtain the source code for review, and that vulnerabilities were found.
Apparently we are not talking about the inherent and well-known issues of e-voting: it can't…
fgrieu
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48
votes
3 answers
What is the difference between a HMAC and a hash of data?
On a recent question it became apparent that there's a significant difference between an HMAC of input data and a hash of input data.
What exactly is the difference between an HMAC and a hash of a span of input data?
Naftuli Kay
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48
votes
1 answer
Second pre-image resistance vs Collision resistance
From Wikipedia:
Second pre-image resistance
Given an input $m_1$ it should be difficult to find another input $m_2$ such
that $m_1$ ≠ $m_2$ and $\operatorname{hash}(m_1) = \operatorname{hash}(m_2)$. Functions that lack this
property are…
ritch
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47
votes
4 answers
Security strength of RSA in relation with the modulus size
NIST SP 800-57 §5.6.1 p.62–64 specifies a correspondence between RSA modulus size $n$ and expected security strength $s$ in bits:
Strength RSA modulus size
80 1024
112 2048
128 3072
192 7680
256 15360
This…
Gilles 'SO- stop being evil'
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47
votes
2 answers
How to choose between AES-CCM and AES-GCM for storage volume encryption
We are using the encryption built into Solaris 11 ZFS, which offers the choice between CCM (CBC counter mode) and GCM (Galois counter mode). What are the pros and cons of choosing each of these cipher modes?
ruief
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47
votes
2 answers
AES CBC mode or AES CTR mode recommended?
What are the benefits and disadvantages of CBC vs. CTR mode? Which one is more secure?
mary
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47
votes
1 answer
Why do all SSH-RSA Keys begin with "AAAAB3NzaC1yc"?
My friend and I have been generating a few SSH2 RSA keys and noticed all the public keys begin with AAAAB3NzaC1yc, with the similarity extending to AAAAB3NzaC1yc2EAAAABIwAAAQEA between two keys generated on the same machine in two successive…
Lord Loh.
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