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1500 questions
77
votes
8 answers
How do I explain zero knowledge proof to my 7 year old cousin?
How do I explain zero knowledge proof to my 7 year old cousin?
Nathan Aw
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77
votes
8 answers
Layman's explanation of encryption backdoors
In the media, I sometimes read about "backdoors" in encryption algorithms. I'd like to understand what such a backdoor actually consists of. Is it:
a) a hidden weakness in the math formulas that can cause security to be broken by brute force in a…
forthrin
76
votes
4 answers
How come Public key cryptography wasn't discovered earlier?
I became interested in crypto lately and read about symmetric and public key crypto algorithms. I understand how crucial the discoveries of the 1970s like RSA, DES and DH were in advancing the technology.
I just don't understand how public key…
pls no
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75
votes
1 answer
Easy explanation of "IND-" security notions?
There are many schemes that can advertise themselves with certain security notions, usually IND-CPA or IND-CCA2, for example plain ElGamal has IND-CPA security but doesn't provide IND-CCA security.
The most common ones are the "IND-" ones,…
SEJPM
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74
votes
3 answers
Signal vs Telegram in terms of protocols?
Some time ago, the question was asked in chat, why MTProto (Telegram's protocol) is supposedly worse than Axolotl (Signal's protocol) as both protocols have been the inventions of their respective companies, thereby "rolling their own crypto", which…
SEJPM
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72
votes
4 answers
How can I use asymmetric encryption, such as RSA, to encrypt an arbitrary length of plaintext?
RSA is not designed to be used on long blocks of plaintext like a block cipher, but I need to use it to send a large (encrypted) message.
How can I do this?
foobarfuzzbizz
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71
votes
3 answers
Why shouldn't I use ECB encryption?
I'm using Java to generate encrypted strings, and I get this warning at build time:
ECB encryption mode should not be used
So I'm wondering why I shouldn't use ECB and what I can use instead?
Rogue
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70
votes
3 answers
Why Curve25519 for encryption but Ed25519 for signatures?
NaCl and libsodium libraries use Curve25519 for authenticated encryption (actually for sharing a key which is used for encryption) and Ed25519 for signatures. What is the purpose of using different primitives for these operations? Why just not to…
user10651
69
votes
2 answers
Is truncating a SHA512 hash to the first 160 bits as secure as using SHA1?
I am from a web development background (I don't know an awful lot about cryptography or how the algorithms themselves work), so I am asking this question in simple terms.
Consider a hash of the word 'test' using…
BadHorsie
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68
votes
4 answers
Why does the FBI ask Apple for help to decrypt an iPhone?
The current debate of the FBI trying to get Apple to assist in decrypting an iPhone made me wonder:
Normally, upon turning on an iPhone, everything is decrypted using a 4-digit pin (or actually, a key that is derived from the PIN with a strong KDF,…
RocketNuts
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64
votes
5 answers
What's the appeal of using ChaCha20 instead of AES?
I read about ChaCha20 being used in TLS by Google, SSH, and towards standardization in general.
What's the appeal of using something other than AES, what with AES receiving dedicated CPU instructions on various architectures to make it so efficent?
JDługosz
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63
votes
5 answers
Technical feasibility of decrypting https by replacing the computer's PRNG
Intel has an on-chip RdRand function which supposedly bypasses the normally used entropy pool for /dev/urandom and directly injects output. Now rumors are going on that Intel works together with the NSA... and knowing that PRNGs are important for…
Luc
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63
votes
6 answers
Why is AES resistant to known-plaintext attacks?
At least it's my understanding that AES isn't affected by known-plaintext. Is it immune to such an attack, or just resistant? Does this vary for chosen-plaintext?
Jeff Ferland
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63
votes
2 answers
Why is $H(k\mathbin\Vert x)$ not a secure MAC construction?
If $H(m)$ is a secure hash function, can't we implement a MAC using $H(k\mathbin\Vert m)$?
However, it seems the more widely used MACs, such as NMAC and HMAC (both originally defined in Keying hash functions for message authentication) use a much…
Anne Nonimus
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62
votes
3 answers
Definition of textbook RSA
What is the definition of textbook or "raw" RSA?
What are some of the properties of textbook RSA?
How does it differ from other schemes based on RSA?
Bobby S
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