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1500 questions
53
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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52
votes
7 answers
Google is using RC4, but isn't RC4 considered unsafe?
Why is Google using RC4 for their HTTPS/SSL?
$ openssl s_client -connect www.google.com:443 | grep "Cipher is"
New, TLSv1/SSLv3, Cipher is RC4-SHA
Isn't RC4 unsafe to use?
Jonas Lejon
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52
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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52
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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52
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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51
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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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
Can one generalize the Diffie-Hellman key exchange to three or more parties?
Does anyone know how to do a Diffie-Hellman or ECDH key exchange with more than two parties?
I know how to do a key exchange between 2 parties, but I need to be able to have a key agreement between 3 or more parties.
hobeau
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50
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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50
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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50
votes
2 answers
AES-GCM recommended IV size: Why 12 bytes?
When using AES-GCM, a 96-bit IV is generally recommended. Most implementations I've seen also use 96-bit. However, I'm unsure on where this recommendation or convention comes from.
Let's assume a shorter IV is bad. Assuming all other constraints for…
Hendrikvh
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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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50
votes
2 answers
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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49
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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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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