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1

While @Anders answer is accurate, I want to extend his case for dropping "low entropy" passwords and I couldn't fit it in a comment. Firstly, I wanted to introduce a parallel. Many ciphers (e.g. DES) have weak keys, which make encryption behave suboptimally. This implies that there is no "flat keyspace" (one where all keys have the same "strength"). If ...


6

In general This depends on what information you are asuming that the attacker has. First, let's asume that the attacker is blind, and perhaps trying to crack a large dump of breached accounts, without knowing that you used that specific algorithm. Then you would be better protected if you discarded 123456 if it comes up, or more realistically, passwords ...


2

The entropy of a password is a quantitative statement about the probability distribution of all the possible passwords. To simplify this, think of a probability distribution as a rule that, given a password, outputs the probability that that password is the one that was chosen. So you really can't put a number to the entropy of a password unless you start ...


1

First, the claim that "/proc/sys/kernel/random/entropy_avail simply gives you the number of bits that can currently be read from /dev/random" is false. The entropy_avail field reads the input_pool.entropy_count, the "output" pool refers to the pool used for urandom (non-blocking pool) and random (blocking pool). As mentioned in this answer, spawning new ...


4

The proper way to calculate password entropy is to look at the password generation method, evaluate how much entropy is involved in the password generation method, and then evaluate how much of that input entropy is preserved by the encoding method. As an example, throwing a fair 6-sided dice once generates approximately 2.5-bits of entropy (note that it's ...


2

KeePass describes some of what they consider here, and it is described with some more detail on page 18 of this excellent paper: Carnavalet, Xavier De Carné De, and Mohammad Mannan. "A large-scale evaluation of high-impact password strength meters." ACM Transactions on Information and System Security (TISSEC) 18.1 (2015): 1. It would be too long to ...


4

Data entropy depends on the observer - there is no absolute measurement of entropy. It's even questionable as to whether or not anything in the universe it at all random, and "randomness" (or, more precisely, related to entropy, unpredictability) is the source or entropy. Unpredictability being the operative term: hard for somebody to predict. If you use ...


2

"Cracking" a password on a website is not subject to the same kinds of brute-force attacks as encryption keys. Unless your source is a breached database, the rate at which you can brute force is limited by the website, which can introduce source-based throttling or blocking, attempt limits, raise flags etc. which makes a simple brute force harder to do. ...


1

The requirement for complexity depends on the lifecycle of a secret (and the value of the secret). If the lifetime is very short because it expires and/or is renewed on a regular basis, not the same level of complexity might be necessary. An account lockout might shorten the lifetime of a password immediately. If an attacker is able to approach just 5 ...


1

There is a difference between a password (passphrase) and an encryption key. Both are used for different purposes. In case a password is used directly as an encryption key it will never be considered secure, just as you described. In many cases you can see KDFs in place, to derive cryptographically strong keys from user passwords (typically PBKDF2 (or even ...



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