Here are the solutions to the problems from the text book. Problems 3, 4, and 5 are different for each system, but can be solved by following the techniques outlined in the book and problem set.

Notes regarding each students submission are included at the end of the document, indexed by student ID number.

1.12.1

a. John copying Mary's homework is a violation of confidentiality. John should not see Mary's homework because to copy homework is cheating.

b. Paul crashing Linda's system is a violation of availability. Linda's system is no longer available to her, or anyone else.

c. Carol changing the amount of Angelo's check from $100 to $1000 is a violation of integrity (specifically, data integrity). The amount written on the check has been changed.

d. Gina forging Roger's signature on a deed is a violation of integrity (specifically, integrity of origin). The deed appears to have come from Roger, when in fact it came from Gina.

e. Rhonda registering the domain name "AddisonWesley.com" and refusing to let the publishing house buy or use that domain name is a violation of availability. The name "Addison-Wesley" is not available to anyone, including the owner of that name, except Rhonda.

f. Jonah obtaining Peter's credit card number, and having the credit card company cancel the card and replace it with another bearing a different account, is a violation of integrity (specifically, integrity of origin). The request appears to come from Peter (else the credit card company would not have honored it), but in reality came from Jonah.

g. Henry spoofing Julie's IP address to gain access to her computer is a violation of integrity (specifically, integrity of origin). The messages from Henry appear to come from Julie's IP address, when in fact they do not.

1.12.3
An example of a situation in which hiding information does not add appreciably to the security of a system is hiding the implementation of the UNIX password hashing algorithm. The algorithm can be determined by extracting the object code of the relevant library routine and disassembling it. (The library must be world readable in order for user programs to load the routine.) Revealing the algorithm does not appeciably simplify the task of an attacker because he knows how to hash passwords, but he still must guess the password itself. An example of a situation in which hiding information adds appreciably to the security of a system is hiding a password or cryptographic key. This is a private piece of information affecting only a single user. Revealing it would give an attacker immediate access to the system.

1.12.4
If the confidentiality of a password is compromised, the attacker may be able to impersonate a user authorized to change data. As integrity requires that only authorized users make only authorized changes to data, and the attacker is not an authorized user, there is a violation of integrity..

1.12.7

a. An example of when prevention is more important than detection and recovery is the nuclear command and control system. By the time an intrusion is detected and recovered from, an attacker could have launched nuclear weapons.

b. An example of when detection is more important than prevention and recovery is in the protection of medical records from unauthorized emergency room personnel. If someone is brought into an emergency room, there may not be time to secure the patient?s permission to access his medical records. But if the records are accessed illicitly, the security personnel should detect it.

c. An example of when recovery is more important than prevention and detection is on a banking computer that maintains account balances. The bank must be able to recover the balance of all accounts to ensure it provides accurate service to its customers. Prevention and detection, while important, are not so important as keeping the balances accurate.

1.12.9

a. The mechanism is secure, because students cannot send or receive electronic mail on the system. It is not precise, as faculty cannot send or receive electronic mail on the system, and the security policy says they are allowed to.

b. This mechanism is precise, because any mail from or to students is discarded. (You can argue this is broad, because students can execute the ?send mail? command, but the mail will never leave the machine. The word ?send? is somewhat ambiguous.)

c. This mechanism is broad, because a student can claim to be a faculty member when answering the question.

1.12.16

1.12.21

9.8.3
One-time pads are rarely used in practise because of the problem of key distribution. As the key must be completely random, it must be generated and distributed using some secure medium (usually by courier). Further, the sender and receiver must ensure they stay synchronized, so the recipient knows where in the key sequence the sender?s key begins.

9.8.6
The book states that Public Key Cryptosystems must meet the following three conditions...

1. It must be computationally easy to encipher or decipher a message given the appropriate key.

2. It must be computationally infeasible to derive the private key from the public key.

3. It must be computationally infeasible to determine the private key from a chosen plaintext attack.

The Caeser cipher is not a public key cryptosystem, as it fails conditions 2 and 3.

9.8.17
Bob and Alice share the key, therefore Bob cannot prove Alice sent the message, as it could have also come from him. There are many ways to modify classical cryptosystems to provide nonrepudiation.


Student ID: 45576022
Score: 63/67

Questions:

(1/1) 1.12.1 - B should include Availability.
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(0/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(4/5) 9.8.17 - Since they share the key, either one could have done it.


(15/15) Question 3
Good job!

(10/10) Question 4


(15/15) Question 5



Student ID: 76873017
Score: 60/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - Good
(1/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Very well done, good job using the shortcut of every word starting with 're'.

(7/10) Question 4
I got a hash of 02374683, not sure where you made the mistake.

(13/15) Question 5
Good idea, except the third column is incorrect, C = 2, not 3.


Student ID: 38080008
Score: 65/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(1/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(/15) Question 3
Well done.

(10/10) Question 4


(15/15) Question 5



Student ID: 78321015
Score: 58/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(1/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(3/5) 9.8.17 - 


(14/15) Question 3
Give more details on your methodology.

(6/10) Question 4
The hash I got was: 57979413

(15/15) Question 5
Collision is correct.


Student ID: 80532039
Score: 66/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmission of key is also a problem
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Very impressive, good job.

(10/10) Question 4


(15/15) Question 5



Student ID: 83313015
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Well done.

(10/10) Question 4


(12/15) Question 5
'candot' is not a word in the english language, but I will assume you meant 'can dot'.


Student ID: 88641030
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Nice graphs

(10/10) Question 4


(15/15) Question 5



Student ID: 47414982
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 37250008
Score: 59/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(0/2) 9.8.3 - You solved question 2, instead of 3.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Good use of deductive reasoning.

(8/10) Question 4
You seem to have forgotten to add your student ID to the hash.

(11/15) Question 5
The collision does not match up quite the same, 2 columns did not match.


Student ID: 79691010
Score: 66/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(0/1) 1.12.4 - The initial problem is a caused by loss of integrity in the key, there is not confidentiality problem.
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - I hope you are never my judge.


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 81220014
Score: 63/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(11/15) Question 5
I get 77229400 as my hash, not 77229440


Student ID: 37861002
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(1/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
The font used for the last 3 questions made part of your solution unreadable for me.

(10/10) Question 4


(15/15) Question 5



Student ID: 81278996
Score: 64/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(7/10) Question 4
E is 4, not 3... my hash was 65901557

(15/15) Question 5
Alb is a new word I know now.


Student ID: 92294016
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 84688019
Score: 54/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(0/2) 9.8.3 - You solved question 2, not 3.
(0/3) 9.8.6 - No solution
(0/5) 9.8.17 - No solution


(15/15) Question 3


(7/10) Question 4
Hash I got is 24807578, you may have made some mistakes.

(15/15) Question 5



Student ID: 85051019
Score: 60/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - point 2 is not correct, sharing keys is also a problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(7/10) Question 4
My hash did not mach yours, I got 54146300

(12/15) Question 5
The hash is one character off, for this text.54846300


Student ID: 45077005
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 50891985
Score: 63/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(6/10) Question 4
You did not include your student number in the hash.

(15/15) Question 5



Student ID: 79179990
Score: 61/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is a big problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(14/15) Question 3
More details needed

(10/10) Question 4


(11/15) Question 5
The hash for this collision is not identical. 83967044


Student ID: 45970985
Score: 62/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(2/5) 9.8.17 - The main reason, is that Alice and Bob share a key.


(15/15) Question 3


(10/10) Question 4


(12/15) Question 5
You added incorrectly, the collision hash is 00123114, not a match.


Student ID: 35595024
Score: 65/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(3/5) 9.8.17 - Bob and Alice share the same key.


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 79956017
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 40790024
Score: 57/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(4/5) 9.8.17 - Transmitting the key is also a problem.


(6/15) Question 3
Your key was 'FIRE', the distance between the repeating words is important, not how long the repitition is.

(10/10) Question 4


(15/15) Question 5



Student ID: 81307993
Score: 65/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(8/10) Question 4
You have incorrect values for some of the letters, 20 for O, etc. resulting in an incorrect hash.

(15/15) Question 5
The hash for the collision matches the incorrect hash in Q4.


Student ID: 27017953
Score: 66/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Glad you enjoyed the question.

(9/10) Question 4
I think you made a mistake in your calcuations, the hash I got was 71948307

(15/15) Question 5
The collision hash is the same, so you must have repeated the mistake.


Student ID: 41169020
Score: 65/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is also a problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(9/10) Question 4
The hash should be 48378295, you must have added incorrectly.

(15/15) Question 5



Student ID: 78058997
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3
Adding the punctuation is a nice touch.

(10/10) Question 4


(15/15) Question 5



Student ID: 82214016
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 36271005
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4
Your wrote your hash down incorrectly, after summing it.

(15/15) Question 5



Student ID: 42349001
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 43453000
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 11721040
Score: 66/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is also a problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 15051956
Score: 62/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(10/15) Question 3
Your key was 'BROWN', incorrectly assuming it was 4 characters caused your problems.

(10/10) Question 4


(15/15) Question 5



Student ID: 80532039
Score: 63/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is also a problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(7/10) Question 4
Incorrect addition, the hash is: 47316988

(15/15) Question 5
Okay...


Student ID: 83556019
Score: 67/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(2/2) 9.8.3 - 
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 39129002
Score: 65/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(1/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is also a problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5



Student ID: 76409994
Score: 66/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(3/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is also a problem.
(3/3) 9.8.6 - 
(5/5) 9.8.17 - 


(15/15) Question 3


(10/10) Question 4


(15/15) Question 5


Student ID: 41192022
Score: 59/67

Questions:

(1/1) 1.12.1 - 
(2/2) 1.12.3 - 
(1/1) 1.12.4 - 
(3/3) 1.12.7 - 
(0/3) 1.12.9 - 
(3/3) 1.12.16 - 
(4/4) 1.12.21 - 

(1/2) 9.8.3 - Transmitting the key is also a problem.
(1/3) 9.8.6 - See the solution
(3/5) 9.8.17 - Bob could have pretended to be Alice.


(15/15) Question 3
Good Job

(10/10) Question 4


(15/15) Question 5