## TOR Extended 3 - Applied Cryptography

• 0:00 - 0:05
And the correct answer is the second and third options.
• 0:05 - 0:08
The first one is not true. Alice can determine the key using
• 0:08 - 0:12
the typical Diffie-Hellman protocol as discussed in the Unit 3
• 0:12 - 0:15
by taking the value G to the power Y and raising
• 0:15 - 0:19
it to the power X. The fourth option is not true; adding the
• 0:19 - 0:21
hash to the message actually increases the size of it.
• 0:21 - 0:24
To see whether second and third options are true, let’s take
• 0:24 - 0:27
a look at what could happen without including the hash.
• 0:27 - 0:30
So Alice picks the value X, calculates G of X and
• 0:30 - 0:33
encrypts G of X with Bob’s public key. She then tries to send
• 0:33 - 0:37
this to Bob. Now, you could intercept the message, then
• 0:37 - 0:40
send a different value to Bob, Bob recalculate the key,
• 0:40 - 0:44
G of X prime Y. Bob would then send G of Y which Mallory
• 0:44 - 0:46
could intercept and send a new value to Alice.
• 0:46 - 0:50
Alice would then calculate a non-sense key and have no
• 0:50 - 0:53
idea that the key she has calculated is worthless. Adding the
• 0:53 - 0:56
hash value of the key to this protocol allows Alice to verify
• 0:56 - 0:59
that she has a valid key that came from Bob and not
• 0:59 - 1:01
from some attacker in the middle.
Title:
TOR Extended 3 - Applied Cryptography
Video Language:
English
Team:
Udacity
Project:
CS387 - Applied Cryptography
Duration:
01:01
 Udacity Robot edited English subtitles for TOR Extended 3 - Applied Cryptography podsinprint_user1 edited English subtitles for TOR Extended 3 - Applied Cryptography podsinprint_user1 added a translation

# English subtitles

## Revisions Compare revisions

• API
Udacity Robot
• podsinprint_user1