53
votes
Accepted
What are requirements for HMAC secret key?
I've added my answer here as I feel the existing ones don't directly address your question enough for my liking.
Let's look at RFC 4868 (regarding IPSec, however it covers the HMAC-SHA256 function you ...
- 33.2k
37
votes
Best Practice: ”separate ssh-key per host and user“ vs. ”one ssh-key for all hosts“
I think this question can be considered from two different angles: security and convenience.
When we create a SSH key pair, we are asked for providing a passphrase to add a more layer to protect the ...
- 471
36
votes
Accepted
JSON Web Tokens - How to securely store the key?
The reality is if other processes can access your process memory or features of your
virtual machine, the game is probably over as you're already compromised. If a process
has access at this level, it ...
- 3,242
26
votes
Accepted
What exactly is a subkey?
This post by user rjh from 2008 in the enigmail forum answers it well:
Originally in PGP 2.6, back in the early 90s, you had just one keypair
and it was used for both encryption and signing. The ...
- 1,606
26
votes
Accepted
Why does an encryption key derived from your lock screen password give you stronger protection (in Android 11)?
In all cases, the encryption key is chosen at random by the device (your mobile phone).
When biometrics are used to unlock the phone, they are checked by a mostly secure module (a TEE, in your case ...
- 9,957
26
votes
Accepted
Is "Math.random" the same as "crypto.getRandomValues" (JavaScript security)
See MDN: Crypto.getRandomValues(), where it reads:
The Crypto.getRandomValues() method lets you get cryptographically strong random values.
(emphasis mine)
In contrast, see MDN: Math.random(), where ...
- 19.6k
24
votes
Accepted
TPM or OpenSSL for key generation?
The difference between using some hardware backed key store (i.e. TPM, HSM, smartcard ...) and a "pure software" solution like openssl genrsa is not so much about the security of the key ...
- 181k
23
votes
What are requirements for HMAC secret key?
According to RFC 7518 - JSON Web Algorithms (JWA):
A key of the same size as the hash output (for instance, 256 bits for
"HS256") or larger MUST be used with this algorithm. (This
...
- 330
23
votes
Accepted
ssh-keygen: What is the passphrase for?
$ man ssh-keygen
[...]
It is possible to specify a passphrase when generating the
key; that passphrase will be used to encrypt the private
part of this file using 128-bit AES.
So this passphrase just ...
- 31.8k
21
votes
Calculate time taken to break AES key
One of my favourite gems on encryption is from Bruce Schneier in his book Applied Cryptography.
One of the consequences of the second law of thermodynamics is that a
certain amount of energy is ...
- 701
21
votes
Accepted
Do you need more than 128-bit entropy?
128 bits of entropy are enough. The whole and only point of considering entropy is to make sure that the system can resist brute force attacks: the space of possible values must be so large that any ...
- 320k
20
votes
Should I hash a password if it is randomly generated
The point of hashing passwords is that if the attacker can gain access to your password file (by breaking into your server, stealing backup media, hacking your hosting provider, etc.) he/she still can'...
- 321
17
votes
Is there any reason someone wouldn't use a longer key?
Each bit of a key increases the difficulty of a brute-force attack exponentially but there is a trade-off. Adding more bits to the key will negatively effect the speed of encryption/decryption. The ...
- 1,916
17
votes
What exactly is a subkey?
Subkeys
Subkey packets are defined in RFC 4880, OpenPGP, 5.5 Key Material Packet. They're only distinguished by another packet ID, and require a binding signature to be actually useful (see below).
A ...
- 23.2k
16
votes
Accepted
Calculate time taken to break AES key
Well, using simple math: If checking one key takes 1000 clock cycles, and the computer has 2,000,000,000 cycles per second, it checks 2 million keys per second. The best case is that the first key you ...
- 7,183
13
votes
Accepted
ECC Public Key length differs from bit representation
An elliptic curve is defined over a finite field of size q for some integer q. Each curve element is a point and has two coordinates X and Y, which are curve elements.
The "size" of the ...
- 320k
13
votes
Is it possible to make a more secure random number generator algorithm by XORing two or more less secure random number algorithms?
I would not recommend combining random number generators in this way without having some underlying theory to support your case.
A simple way to illustrate the issues is to consider the behavior of ...
- 137
12
votes
What are requirements for HMAC secret key?
The RFC 2104 defining HMAC functions answers this question:
The key for HMAC can be of any length (keys longer than B bytes are
first hashed using H). However, less than L bytes is strongly
...
- 19k
12
votes
Is "Math.random" the same as "crypto.getRandomValues" (JavaScript security)
Your friend is correct; always use Crypto.getRandomValues instead of Math.random for anything related to security.
Math.random is designed for statistical simulations; and the numbers it produces ...
- 33.5k
11
votes
SSH key-type, rsa, dsa, ecdsa, are there easy answers for which to choose when?
Use RSA. Not for security reasons, but for compatibility reasons.
I don't recommend using DSA keys. As of OpenSSH 7.0, SSH no longer supports DSA keys by default. As the release notes for OpenSSH ...
- 98.3k
10
votes
Accepted
Alternatives to HTML's deprecated <keygen> for client certs?
In this post in the chromium forum there are alternatives mentioned
Within the browser space, alternatives exist such as:
Use the device's native management capabilities if an enterprise use case. ...
- 1,682
10
votes
Accepted
What's the best length for randomly generated passwords? (Security vs. compatibility)
If your passwords are n characters randomly drawn, with equal probability, from a set of 95 characters (which is about all the ASCII printable characters minus space), then each character gives you ...
- 10.1k
10
votes
Accepted
Rotating encryption keys - how does it work?
In layman's terms, rotating an encryption key implies:
Generate new key(s)
Re-encrypt all data that was encrypted using the old key, using new key(s)
Delete old encrypted data and old encrypted key
...
- 71.7k
9
votes
Accepted
Diffie-Hellman key exchange
With big numbers, Diffie-Hellman looks like this: we work modulo a big prime p, and we start with a conventional big integer g (in the 2..p-2 range). Each integer modulo p represents an achieved ...
- 320k
9
votes
Accepted
What is the exact meaning of "Keying material"?
What is the exact meaning of “Keying material”?
Keying material is a more general and fancy term for "secret keys of (unspecified) format, length and amount", where the "unspecified&...
- 9,480
9
votes
Rotating encryption keys - how does it work?
The meaning of rotate is going to depend on your data owner’s security policy.
It may help to understand how keys are often managed in a key-management system using a key lifecycle state chart. A ...
- 33.5k
9
votes
What research suggests that user's mouse movements are (not) sufficiently unpredictable for secret key generation?
I do not believe there are any research papers that describe the unpredictability of the neuromuscular system in the context of computer security and at the sample rates that are relevant, so I can't ...
- 63.8k
9
votes
Accepted
Preparing to change over to new GPG-key - what to do with my old ones?
Thanks for the comment response, that helped a little bit.
These are general recommendations, YMMV and you can always tweak them to your own needs. This is just a good place to start and things to ...
- 791
8
votes
Should I hash a password if it is randomly generated
There are two levels:
You need some hashing as a second line of defence, so that what you store on the server (I call "server" the system which does the authentication by verifying a given password) ...
- 320k
Only top scored, non community-wiki answers of a minimum length are eligible