I/O Side Channels

Question 1

In password timing attacks, how many attempts does it take?

Answer 1

26*n, instead of 26^n

Question 2

What are pros (for attacker) for I/O SC?

Answer 2

• computers have built-in support for gathering information about SC
• easy to send anonymous packets to remote systems

Question 3

How to mitigate timing SC

Answer 3

use a constant time implementation => response time should not depend on any secret information

Question 4

better implementation of password checker and why setting ret = false is bad

Answer 4

ret = (s1[i]) == s2[i]) & ret.

setting ret to false adds an extra instruction!

Question 5

cons of constant time implementation

Answer 5

• hard to do (and can depend on compiler and hardware)
• bad for performance => always exec worst case
• may introduce new limitations (max pw len)
• must consider binary-level code and hw implementation

Question 6

how can compiler and hw interfere with better password checker impl?

Answer 6

compiler might not have the instructions to do the op in constant time or might try to optimize. hardware might have optimizations

Question 7

Types of I/O Observable SC attacks

Answer 7

1. timing packets in interactive connections

2. packet size (image vs text), can create amount/size/timing of images and text to fingerprint webpages

Question 8

Benign uses of I/O SCs

Answer 8

1. heartbeat messages

2. ensure software attestation (making sure sw has not been changed)

Question 9

how does sw attestation SC work?

Answer 9

design checksum calculation so that it is faster to compute using program memory and fail attestation if it takes too long