Linked Questions

135
votes
6answers
224k views

Why most people use 256 bit encryption instead of 128 bit?

Isn't 128 bit security enough for most practical applications?
88
votes
4answers
18k views

Will quantum computers render AES obsolete?

This is a spin off from: Use multiple computers for faster brute force Here's at least one source which says that quantum computers are on the way to being able to break RSA in the not too distant ...
62
votes
6answers
23k views

Pattern to allow multiple persons to decrypt a document, without sharing the encryption key?

Current setup We have a service that allows users to upload documents through a website and stores the uploaded documents encrypted on disk. The documents on disk are encrypted with a per-user key, ...
32
votes
11answers
10k views

One liner to create passwords in linux?

How do you create a readable password using bash with one line? What if i'm looking for 128 bits of entropy? EDIT By readable I mean the 94 printable ascii characters (without space). It can use ...
28
votes
3answers
5k views

Use multiple computers for faster brute force [duplicate]

I've watched Mr. Robot lately and can't stop thinking why it was so hard to decrypt files encrypted using AES encryption with a 256-bit key. Let us say the only method to find the key is through brute ...
26
votes
7answers
3k views

Is sha1sum still secure for downloadable software packages signature?

We use sha1sum to calculate SHA-1 hash value of our packages. Clarification about the usage: We distribute some software packages, and we want users to be able to check that what they downloaded is ...
21
votes
6answers
4k views

Can any password hash ever be secure?

My understanding is the the main reason MD5 is insecure, is that it can be calculated too quickly, allowing too many attempts to be tried. People recommend instead using a hash that has been designed ...
22
votes
4answers
7k views

Which hash-length is more secure?

If a hash algorithm has an option for selecting the output-hash-length (e.g., 128 vs. 512 bits), and all other aspects of the hash function are the same, which hash-length is probably more secure/...
27
votes
2answers
36k views

Recommended options for LUKS (cryptsetup)

I'm looking for recommended options for cryptsetup to create fully encrypted SSD (SanDisk SSD U100 128GB), which achive: Timing O_DIRECT disk reads: 1476 MB in 3.00 seconds = 491.81 MB/sec Timing ...
22
votes
2answers
1k views

Does holding an AES-encrypted string and its cleartext from a database help an attacker in decrypting other parts of the database

I have a question regarding Encryption. Say an attacker stole my entire database. In that database all the data was encrypted. If the attacker took one piece of encrypted data and for some reason knew ...
17
votes
4answers
33k views

What do key size and block size mean in cryptography?

Can some one simply explain the meanings and the difference between symmetric key and block size. Why 64 block size not safe any more and they increase it to 128 (AES,...,Serpent)? And what about key ...
10
votes
6answers
5k views

Most secure data storage?

What is most secure data storage currently available and suggested by specialists, to store digital data in digital medium (without making hard copy of data onto paper or other type of medium, than ...
17
votes
4answers
2k views

Is there any reason someone wouldn't use a longer key?

Larger key sizes are said to be more difficult to bruteforce; is there any reason someone would then decide to instead use a smaller key? Is there any negative effect in using a larger key size, such ...
8
votes
4answers
9k views

Calculate time taken to break AES key

A 256 bit AES key is required to be broken using the brute force method on a 2GHz computer. How long would it take to break the key in the best case and in the worst case situations? Assume that 1000 ...
15
votes
4answers
4k views

Is there a length beyond which increasing password length provides no additional security?

Assuming that the password is stored hashed and salted, and that it is a string of random characters, is there a point where adding to password length doesn't add security? Since the hash will have a ...
4
votes
3answers
9k views

Brute forcing ssh keys

My problem is a common one: I deleted my SSH key, and forgot to set rm to point to a .trash file. I have the public key, and I need to get in this server. I am not doing this on anyone else's server. ...
12
votes
1answer
16k views

Will double encryption increase the security of cipher vs bruteforce?

Assume I have a function encrypt(mes,key) where mes is the message, and key is the key. The length of key is 64 bits. Last but not least: assume the only way to crack my cipher is a brute-force attack....
7
votes
3answers
2k views

Why do we have such big keys?

In Chapter 7 of Applied Cryptography, Bruce Schneier claims that, due to thermodynamic limitations, "brute-force attacks against 256-bit [symmetric] keys will be infeasible until computers are built ...
15
votes
2answers
22k views

Why does Google prefer ECDHE-RSA-AES128-GCM-SHA256?

I want to configure my new mail server secure as possible and wondering about the used cipher while connecting to Googles SMTP server. I'm curious why they prefer the cipher ECDHE-RSA-AES128-GCM-...
5
votes
2answers
2k views

Designing a cryptographic file-sharing protocol

As a learning project, I am trying to implement a secure way to share files with a friend over dropbox. (I am not looking for existing software, I am doing this in order to learn how to do this right.)...
13
votes
3answers
1k views

Can signing too much compromise a private key?

Can a collection of many messages signed with the same private key be abused to either forge signatures so some (but not all possible) messages, or even worse to reconstruct that private key with less ...
12
votes
3answers
3k views

ProtonMail security concerns

This TED talk brought me here. First of all, to those who created ProtonMail: Nice job!!. Regardless of what people say, it's definitely a big step forward from tradition options like Hotmail, Gmail ...
11
votes
2answers
1k views

Unseen.is encryption claims revisited with their proprietary, patented “xAES” algorithm

I had asked last year about the encryption claims by the web service called https://unseen.is. The very same service that had claims of "beyond army level encryption", "4096 bit keys" etc. This is the ...
12
votes
2answers
2k views

How can a passphrase with 256 bits of entropy practically be constructed & memorized?

Quoting Wikipedia: A password with, say, 42 bits of strength calculated in this way would be as strong as a string of 42 bits chosen randomly[.] Assuming that interpretation is correct, combined ...
10
votes
1answer
11k views

Why is secp521r1 no longer supported in Chrome, others?

Found a few issue threads, notably for Chrome (Chromium issue #478225), and the browser does appear to have dropped support for the secp521r1 curve (can test your browser using SSLLabs). There were ...
7
votes
3answers
7k views

For how much time should I randomly move the mouse for generating encryption keys?

When creating a Truecrypt volume, there is the wizard page in which the user is told to randomly move the mouse (the longer the better) to generate entropy, and that it will significantly increase the ...
5
votes
2answers
4k views

Do you need more than 128-bit entropy?

UUID uses 128-bit numbers. Currently it is not feasible to randomly produce two UUIDs that are the same. Does that mean 128 bits of entropy is suitable for all cryptographic operations? I would ...
8
votes
1answer
8k views

PGP RSA key size - encryption/decryption time

From what I've read, PGP only uses the pub/priv keys for encrypting/decrypting a symmetric key used for actually encrypting/decrypting data. I'd reasonably assume that longer asymmetric keys wouldn't ...
5
votes
1answer
7k views

Is there a maximum allowed key size in the USA?

I've heard that using encryption outside military use has been illegal for a long time in the USA. However, I've also heard that when the regulation was updated, limits were put on encryption strength ...
5
votes
2answers
3k views

Are RSA 2048, ECDSA, and the SHA uncrackable in the sense that AES-256 is uncrackable?

The answer https://security.stackexchange.com/a/25392 has seemingly shown that AES-256 will not be directly cracked for at least the next 200 years (unless we manage to harvest the energy output of ...
10
votes
2answers
479 views

What's the chance of two PGP keys being exactly identical?

In the real world, millions of PGP keys are created every day, what is the probability (chance) of creating two identical keys? In different places, by different people?
6
votes
1answer
5k views

Security of bcrypt/sha256 key used with AES to encrypt a file

I'm looking to encrypt files using secure hashing and encryption algorithms in Python. Having used bcrypt in the past, I decided to use it for my passphrase calculator, then pass the output through ...
2
votes
2answers
3k views

How long would it take a single Processor with the AES-NI Instruction Set to bruteforce an AES Key?

I know that it seems like a stupid question - since it's note feasable to break AES without a quantum computer but I'm curious anyway. I read on wikipedia that the best known attack on AES-128 takes ...
2
votes
3answers
3k views

how long does it take to brute force varying encryption standards?

Let's say I want to encrypt information in a database. What would be the best encryption algorithm to use and why. I was thinking AES, since it's widely used as a government standard, but if the ...
7
votes
2answers
419 views

Why standards organizations give so short protection times for 128 bit encryption?

According to this and this, seems even 128 bit encryption should remain secure for a much longer time than what security organizations say. I saw the standards with this: http://www.keylength.com/en/...
4
votes
2answers
1k views

SSL Bit Length History

Sometimes I see web pages advertising a site's support for SSL with a given bit length (commonly 128), and saying that visitors need certain browsers that support this. Is 128-bit SSL common now, or ...
5
votes
3answers
2k views

Password strength metrics

In the question Source code as password I suggested using a combination of entropy and as @Lawtonfogle put it 'meatspace difficulty'. As suggested in the xkcd comic correct staple horse battery is a ...
-1
votes
3answers
1k views

find password and iv of an encoded string knowing the decoded string

If I would know the clear and encoded versions of a string could I somehow find the password and.or iv that wore used to encode it? Encoding done with open_ssl aes-128-cbc.
2
votes
4answers
619 views

Strategies to store/remember very long password?

If future proof encryption is - in theory - possible it will require long password. What are some of the strategies for storing or remembering very long - in this case rarely used - password? For ...
3
votes
2answers
734 views

What risk does commoditized dedicated SHA256 processors pose to IT Operations?

With the advent of GPU-based computing, and now commoditized/dedicated SHA256 processors, what risk does this hardware pose to cryptography? What security algorithms should be closely watched or ...
3
votes
3answers
637 views

Is encryption key length limitations by governments norm?

Today my internet service provide gave me a customer agreement form to fill in. I found following line in it: Permission limit for Encryption is 40 bit key per length in RSA algorithms, If customer ...
0
votes
3answers
3k views

Transmitting private keys between devices? [duplicate]

I have an app where a users' device create a public/private key and all communication to this user is done by encrypting against their public key, which is stored on a server and sent to other clients ...
1
vote
2answers
365 views

Are the Microsoft Windows images found on the internet safe?

Microsoft has stopped offering the Windows images for download. It is now only possible to get the image if one has a key of a retail version of the corresponding OS. The question is now, whether the ...
0
votes
1answer
890 views

Is there an AES 256 LUKS encryption option in Fedora? [closed]

I have certain information on my drive that I don't want anyone (not even me ;) ) to gain access to. I read recently that Fedora only offers EAS 256 LUKS encryption. This just isn't secure enough ...
-1
votes
3answers
130 views

Are 21 characters enough to restore a PGP key?

The german e-mail hoster web.de offers PGP encryption with Mailvelope now. To transfer your private key to another browser, you can use a 21 characters long recover key. How does this affect the ...
4
votes
1answer
340 views

Is there a PRNG in Java with a period of at least 256 bits?

From what I can tell, Sun JRE/JDK's are limited to only providing 128-bit strong cryptography without downloading an unlimited strength jurisdiction policy files. My question is, if I install theses ...
2
votes
1answer
189 views

Usefulness of bcrypt(UUIDv4())

One of my colleagues is working on securing OAuth 2 client IDs and secrets for our OAuth server and he has come up with this scheme where he would not only use UUID v4 to generate random values, but ...
1
vote
1answer
223 views

How long can a pkcs#8 passphrase be?

A program is using a private key to read messages. To improve security, besides randomness, I'm trying to create the longest passphrase that makes sense. How long should it be? After which amount of (...
1
vote
1answer
270 views

Does pppd encrypt traffic?

There is pppd program that can be used to create point-to-point conections over various channels (including other network). It supports authentication and compression. But does it encrypt traffic or ...
1
vote
1answer
314 views

KeePassXC & Yubikey HMAC-SHA-1 vs 40+ Character Password

Looking at the implementation of the Yubikey 4 HMAC-SHA1 mode for KeePassXC, I want to know: Isn't the HMAC-SHA1 challenge response less secure than a 40+ character password? From what I know, the ...

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