Authentication
10 important questions on Authentication
Name three examples of passwordless authentication.
- SSH (Secure Shell): Remotely access a (computer) system with end-to-end encryption.
- FIDO Authentication: Developed by FIDO Alliance to get rid of passwords.
- Web authentication (WebAuthn): Part of FIDO2 and currently in the making. An interface for authenticating users to web applications and services with public-key cryptography.
Remote login is a process in which user can login into remote computer and use its services as if it were local machine.
What is user authentication?
What is user registration?
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Is SHAKE128 good for password hashing? If not, give a better hash function alternative.
We need resource-hungry hash functions, like scrypt, bcrypt or ARGON2. These slower functions will automatically also slow down the attacker.
Resource-hungry means an application is using tremendous amounts of CPU time slot, memory, storage, and/or network bandwidth.
What is the entropy of a password? And do we want a high or low entropy?
It expresses the amount of uncertainty that an attacker has about a password.
We want a high entropy with respect to any reasonable attacker.
What is the formula of entropy? What unit do we use for the entropy of a password?
The unit is bits.
Assume we have a cube die that is biased in the following way:
- Faces 1 and 2 have the same probability.
- Faces 3, 4, 5 and 6 have the same probability.
- The probability of face 1 is twice that of face 3.
What is the value of the entropy of the outcome of a dice roll?
- If we take a bag and put 1, 2, ... 6 in the bag they all have the same probability.
- If we place 1 and 2 in there once more, then they (1 and 2) now have twice as much probability of getting draw randomly.
- If we count the total elements in the bag we get 6 + 2 = 8.
- For 1 we have 2/8 (= 1/4). For 2 we also have 2/8 (= 1/4). For 3 we have 1/8 and the same for 4, 5 and 6.
What is injective encoding?
When are fixed-length input strings injective? When are variable-length input strings injective?
Variable-length input strings = Only injective with Length-Value (LV) encoding. This means each string is encoded as a sequence of two elements
- L: A byte that species the length of the string
- V: The string itself
What is the value of the entropy of a fair coin toss?
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