51 votes
Accepted

Why haven't (most of) the Zodiac Killer's letters been decrypted?

The Zodiac killer ciphers are an interesting case. As there were four ciphers sent to the local papers, I will address each in turn. They do share some common traits however. They are each their own ...
WhataTiberius's user avatar
50 votes

SSH - If Eve has the passphrase and public key, can she derive the private key?

The private key is unrelated to the passphrase. So is the public key. The public key is also generally stored unencrypted, even when the private key is protected by a passphrase. (Exceptions may exist ...
user's user avatar
  • 7,785
26 votes

Why haven't (most of) the Zodiac Killer's letters been decrypted?

You're assuming that they're actually encrypted. A lot of crazy people have written things that nobody understands. Just because the author thinks they're in code doesn't necessarily mean that the ...
tylerl's user avatar
  • 83.3k
24 votes

SSH - If Eve has the passphrase and public key, can she derive the private key?

The passphrase guards against accessing the private key The passphrase is meant to guard the private key in the event of physical access. If the hacker can sign on to your server and can access your ...
John Wu's user avatar
  • 9,311
14 votes
Accepted

Does it weaken the encryption of SSH to use compression?

Compression before encryption is a problem if the attacker can control parts of the transferred data and then use the detectable compression ratio (i.e. amount of transferred data vs. original data) ...
Steffen Ullrich's user avatar
10 votes
Accepted

Will prepending random data (of random length) result in more secure communication?

No, this won't provide any improvement for encryption with any decent cipher. If a cipher is so bad that a known-plaintext attack is capable of fatally breaking it, then the cipher is worthless. A ...
forest's user avatar
  • 66.6k
7 votes

Are stronger passwords safe in case of a breach?

A stronger password is almost always better than a weak password. In the event of a breach, the details of the hashing and salting of passwords become very important. If the server used plain text, ...
Meir Maor's user avatar
  • 1,682
7 votes
Accepted

Should we be using SHA3? (2017)

I'm not convinced that we should. SHA-3 has some nice features for sure, but for the reasons I list below, I would probably suggest using SHA-2 or BLAKE2 for the time being. Even NIST themselves say:...
JZeolla's user avatar
  • 2,996
7 votes

With a very large number of GUIDs, can one predict the previous and subsequent GUIDs that will be generated?

It would depend on the implementation of the GUID/UUID library. Determining the internal state of a pseudo-random number generator varies widely based on which one you're talking about. Many GUID/...
John Downey's user avatar
  • 1,945
7 votes

How to determine what type of encoding/encryption has been used?

This is very weak security on all fronts! The plaintext is P4$$w0rdP4$$w0rd and it's encrypted using XOR encryption, with the key CdZ4MLMPgYtAE9gQ80gMtg==. This produces the ciphertext posted by the ...
mti2935's user avatar
  • 23k
7 votes
Accepted

Can a Keypass file theoretically be cracked offline?

What about a password manager's database? You know nothing about the content of the file. How do you know you did manage to crack it? This assumption is wrong. You don't know the entries, but in this ...
vidarlo's user avatar
  • 16k
5 votes

SSH - If Eve has the passphrase and public key, can she derive the private key?

It might be possible to derive your private key from the public key (it is only thought that no-one knows how to do it efficiently), but the passphrase won’t help at all. You should understand that ...
user2233709's user avatar
5 votes

Are stronger passwords safe in case of a breach?

When there's a breach … when talking to to someone with a genuinely random password – eg one generated by a good password manager – is it fair to say you are probably safe? Theoretically, yes (under ...
e-sushi's user avatar
  • 1,306
4 votes
Accepted

Can you find the ransomware key if you already have decrypted files?

Yeah, you've pretty well answered your own question, but here's some more context. It turns out that what you've come up with has a name, from wikipedia: The known-plaintext attack (KPA) is an ...
Mike Ounsworth's user avatar
4 votes

Is there a difference between encryption keys and encryption certificates?

Certificates are used to create a Public Key Infrastructure (PKI). Generally the X.509 form of certificates are used, in which case the PKI is called PKIX, after the standard. The private keys within ...
Maarten Bodewes's user avatar
4 votes

Can a Keypass file theoretically be cracked offline?

Adding to what @vidarlo correctly describes, the answer to your question is: Yes, the keypass file can theoretically be cracked. Can it practically be cracked? That depends on the strength of your ...
lab9's user avatar
  • 544
3 votes
Accepted

Where to submit an algorithm for analysis?

There is no easy way to achieve this. You first have to read enough literature to understand why current algorithms are designed the way they are, and how earlier algorithms have been broken. Next ...
kasperd's user avatar
  • 5,482
3 votes

Why is it necessary to minimize redundancy in the ciphertext of a stream cipher?

The main problem with the bug you are describing is that 0 appears more frequently in certain bits of the output stream. The most common attack is that an attacker can make a victim create millions of ...
Beurtschipper's user avatar
3 votes

Targeted acoustic keylogging attack prevention

In my opinion acoustic cryptanalysis is more of a proof of concept then to be used in real applications. What is possible to do? A few years ago guys from MIT (if I am not wrong) were able to log ...
Lucian Nitescu's user avatar
3 votes

Vulnerabilities due to improper use of cipher's mode of operation?

There are lots of examples: Given two identical blocks of plaintext, ECB mode produces two identical blocks of ciphertext (for the same key). This allows for a distinguishing attack where the ...
Polynomial's user avatar
  • 135k
3 votes

How do RSA smartcards prevent key exfiltration?

No common modern ciphers or MAC constructions - certainly none of the ones that a smartcard or other HSM will even support - are known to be vulnerable to any cryptanalysis where chosen-plaintext or ...
CBHacking's user avatar
  • 47.5k
2 votes

Targeted acoustic keylogging attack prevention

You could for instance get the person to use such programs as language apps to get an acoustic fingerprint of the sets of letters. Just imagine the permutations of 'a quick brown fox jumps over the ...
Munchen's user avatar
  • 21
2 votes

Correct way to get a number from 0-9 from a random byte?

There are two ways you can do this. First is to split the byte into two 4 bit numbers. If the 4-bit number is above 9, discard it. You can get up to 2 digits per byte this way. Another way you could ...
Spl1ce's user avatar
  • 21
2 votes
Accepted

Clarifications regarding testing the cipher using NMAP scan

<table key="TLSv1.2"> is not configuration. The section you are referring in the NSE script explain the expected XML output. ssl-enum-ciphers.nse script will enumerate through all tls....
ayomawdb's user avatar
2 votes
Accepted

Is there a difference between encryption keys and encryption certificates?

A key is generally just the data needed for encryption. A certificate contains additional info, such as domain the key belongs to, the organization it belongs to, when it expires etc. Certificates are ...
Peter Harmann's user avatar
2 votes

SSH - If Eve has the passphrase and public key, can she derive the private key?

Can they derive the Private key? - I presume yes with enough time. The passphrase is just used to encrypt the storage of the private key on the client system, so it is only useful if they have the ...
Peter Green's user avatar
  • 5,200
1 vote

Storage of secret key in resource-constrained sensor nodes

Generally the "master key" is different from derived device keys. You do not store the master key in the devices. Where to store the device key is dependent, but generally you'd store it in flash / ...
Maarten Bodewes's user avatar
1 vote

Using Chacha20 with a NULL nonce

Another answer has the rule so how about some intuition: ChaCha permutes a block of data into an unpredictable block of data and XORs it with your plaintext. Because XOR is reversible, the same ...
foreverska's user avatar
  • 2,037

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