midterm rev

Question 1

the /etc/passwd file is called password file but in reality it doesn’t contain account passwords, explain why?

Answer 1

Passwords are stored in hashed form outside the /etc/passwd file for enhanced security

Question 2

what is the purpose of the salt in the /etc/shadow file?

Answer 2

to prevent precomputed password attacks by adding randomness and strengthening password hashing

Question 3

write a command to revoke user’s U access on all files without interfering with other users permissions

Answer 3

1) check user’s U permissions
getfacl -u U <filename>
2) revoke access
setfacl -m -u:U:--- <filename>
OR
setfacl -m -u:U:0 <filename>
3) verify you have revoked access
getfacl -u U <filename></filename></filename></filename></filename>

Question 4

for i =1, i<=n {
setfacl -m -u:U:— filei
}
is this operation more efficient in terms of complexity than removing U’s rights to file fn only? explain and justify

Answer 4

• the algorithm has a time complexity of O(n) as it is iterating through n files
• while the second command has a constant time complexity of O(1)
• in terms of time complexity then the single line command is more efficient