Lesson test: Passwords

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Passwords

1.[3p]
Each increment of the bcrypt work factor doubles the work. How many times slower is work factor 12 than work factor 5?

CorrectNot quite: 128

2.[3p]
What does a per-user salt actually prevent?

One computation being reused against many accounts, including precomputed tables of common passwords

Correct

An attacker from guessing any individual password

The answer is: One computation being reused against many accounts, including precomputed tables of common passwords

The password hash from being reversed

The answer is: One computation being reused against many accounts, including precomputed tables of common passwords

The stored hash from being read out of a database backup

The answer is: One computation being reused against many accounts, including precomputed tables of common passwords

3.[3p]
Match each function to the property that decides where it belongs.

Argon2id
scrypt
bcrypt
PBKDF2

memory hard but with parameters that interact awkwardly
the only one in Web Crypto, and the weakest of the four
memory hard with all three dials, the default choice today
fine for existing systems, silently truncates input at 72 bytes

Show the answer

Argon2id: memory hard with all three dials, the default choice today scrypt: memory hard but with parameters that interact awkwardly bcrypt: fine for existing systems, silently truncates input at 72 bytes PBKDF2: the only one in Web Crypto, and the weakest of the four

4.[3p]
A password hash takes 250 ms and 8 cores are free for hashing. What is the ceiling in logins per second?

CorrectNot quite: 32

5.[2p]
Which of the three tuning dials is the one an attacker cannot make cheaper with custom hardware?

CorrectNot quite: memory

6.[2p]
NIST SP 800-63B recommends forcing every user to change their password every 90 days.

True

The answer is: False

False

Correct

7.[3p]
Which of these does NIST SP 800-63B actually recommend?

Select all that apply

Accepting passwords of at least 64 characters

Correct

Checking the chosen password against a list of known-breached values

Correct

Allowing paste, so password managers work

Correct

Requiring an uppercase letter, a digit and a symbol

The answer is: Accepting passwords of at least 64 characters, Checking the chosen password against a list of known-breached values, Allowing paste, so password managers work

8.[3p]
The Pwned Passwords check hashes the candidate with SHA-1. Why is a broken hash the right choice here?

The digest is a public lookup key, not a stored credential, and the check needs it fast, deterministic and unsalted

Correct

SHA-1 is only broken for passwords longer than 72 bytes

The answer is: The digest is a public lookup key, not a stored credential, and the check needs it fast, deterministic and unsalted

The service re-hashes it with Argon2id on arrival

The answer is: The digest is a public lookup key, not a stored credential, and the check needs it fast, deterministic and unsalted

Any weakness is cancelled by sending only the first five characters

The answer is: The digest is a public lookup key, not a stored credential, and the check needs it fast, deterministic and unsalted

9.[3p]
Why should a login handler verify against a fixed dummy hash when no account matches the email?

Otherwise the response returns far faster for unknown addresses, and timing alone reveals which accounts exist

Correct

Otherwise the database throws on a null hash

The answer is: Otherwise the response returns far faster for unknown addresses, and timing alone reveals which accounts exist

It keeps the hash parameters warm in cache

The answer is: Otherwise the response returns far faster for unknown addresses, and timing alone reveals which accounts exist

It stops the attacker from learning the Argon2id parameters

The answer is: Otherwise the response returns far faster for unknown addresses, and timing alone reveals which accounts exist

1.[3p] Each increment of the bcrypt work factor doubles the work. How many times slower is work factor 12 than work factor 5?

2.[3p] What does a per-user salt actually prevent?

3.[3p] Match each function to the property that decides where it belongs.

4.[3p] A password hash takes 250 ms and 8 cores are free for hashing. What is the ceiling in logins per second?

5.[2p] Which of the three tuning dials is the one an attacker cannot make cheaper with custom hardware?

6.[2p] NIST SP 800-63B recommends forcing every user to change their password every 90 days.

7.[3p] Which of these does NIST SP 800-63B actually recommend?

8.[3p] The Pwned Passwords check hashes the candidate with SHA-1. Why is a broken hash the right choice here?

9.[3p] Why should a login handler verify against a fixed dummy hash when no account matches the email?

1.[3p]
Each increment of the bcrypt work factor doubles the work. How many times slower is work factor 12 than work factor 5?

2.[3p]
What does a per-user salt actually prevent?

3.[3p]
Match each function to the property that decides where it belongs.

4.[3p]
A password hash takes 250 ms and 8 cores are free for hashing. What is the ceiling in logins per second?

5.[2p]
Which of the three tuning dials is the one an attacker cannot make cheaper with custom hardware?

6.[2p]
NIST SP 800-63B recommends forcing every user to change their password every 90 days.

7.[3p]
Which of these does NIST SP 800-63B actually recommend?

8.[3p]
The Pwned Passwords check hashes the candidate with SHA-1. Why is a broken hash the right choice here?

9.[3p]
Why should a login handler verify against a fixed dummy hash when no account matches the email?