Homework 3, Random Cipher.

Short Description:

Write a program that will encrypt and decrypt messages using a random cipher method.

Goals

When you finish this homework, you should have:

Implemented a class according to a given design.
Written a test driver for your class.
Written program to employ your class.

Formal Description

The Caesar cipher encrypted messages by shifting each letter by a fixed amount, normally three. The letter a + 3 = d so a -> d, b -> e, ... x -> a, y->b and z->c. To decrypt this cipher, just reverse the direction. Unfortunately this is an easy cipher to break. You could use other shift amounts, but it has little impact, it is still easy to break the fixed shift cipher.

A more secure simple cipher is the stream cipher. In this method, a pseudorandom stream is used to encrypt the next letter. For this homework you will implement such a cipher.

For this cipher you will use the random number generator rand_r which produces a sequence of pseudorandom values. You need rand_r as you will be encrypting/decrypting multiple streams at once.

To Encrypt a message

Assure that the seed is set correctly
For each character in the message
- If the character is a letter, encrypt the letter and add it to the cipher text.
- Otherwise add the character to the cipher text.

Messages can be decoded in a similar manner.

To encrypt a letter

generate a random shift amount
"add" that shift amount to the letter to get the encrypted letter.

To decode a letter

Generate a random shift amount
"subtract" that shift amount to the letter to get the encrypted letter.

If the encryption and decryption both start with the same seed, the encryption will be reversed by the decryption. It is therefore necessary for both the process encrypting a message/letter and the process decrypting the message/letter to start with the same random seed.

The encryption process will be greatly simplified if you had a "key" class that could

Be initialized to a seed.
Encrypts/decrypts a letter as described above.
Report the current state
- The current seed
- The current number of encryptions performed.

For this project:

10 points, create a key class.
- It should be called KeyT, and implemented in KeyT.h and KeyT.cpp
- The KeyT class should have:
  - a default constructor that initialize the seed to 1.
  - an overloaded parameterized constructor so the user can pass in a seed.
  - an Encrypt method that takes a character and returns the encrypted character. (see below).
  - a Decrypt method that takes a character and returns the encrypted character. (see below).
  - a Steps method that returns the number of characters that have been encrypted since the key was set/changed
  - a Seed method that returns the current seed.
- Encryption/decription
  - Should shift as described above.
  - Non-alphabetic characters should not be shifted. ie # shifted is #.
  - The case of the letter should be preserved. ie A shifted by 3 is D, a shifted by 3 is d.
  - I used a private method do do both encryption and decryption, based on a parameter.
- In addition, you should overload the stream insertion operator so that a KeyT will produce:
  - ```
  Seed: seed value Steps: number of times the key has been called  
```
- So if a key has a seed of 1699353390 and has been used 35 times,the output would be:
- ```
Seed: 1699353390 Steps: 35
```
10 points, create a test driver to make sure your KeyT class works.
- This should be called keyTest.cpp
- It have a set of messages that
  - are turned into a crypt text by encryption
  - Are then turned back into a plain text by decryption
  - Are then compared with the original to assure the process worked.
- These messages should include upper and lower case letters as well as spaces and other symbols.

20 points, create a program that decrypts a series of messages.

The program should

Process the file input.txt.

After reading all configuration information, print all encoded/decoded messages one per line.

Each message should be printed in the format

********************************************************************************
Processing: text
Stream: stream number
Direction: direction code
New Message: encrypted/decrypted message

After the file is processed
- Print another line of stars
- Print a final report
  - Note the key information is from the overloaded stream insertion operator.
  - And each stream line starts with a tab.

The file

Should be called input.txt

Contains:

Contains an integer n, 1 ≤ n ≤ 10, the number of communication streams contained in the file.
This will be followed by n seeds, one for each communication stream.
This will be followed by a series of messages, one per line. Each line will contain:
- The number of the communication stream
- A colon
- The letter E if you are to encrypt the message, the letter D if you are to decrypt the message.
- A colon
- The message to be decrypted or encrypted.

An example input file

3
1234
4321
1921
1:E:Hello World!
1:D:Mvuge Eyygm!
2:E:The quick brown fox jumps over the lazy dog!  
2:D:Ccl wopqk lrlag vek pkxfl xysu uio cjjo nwk!
3:D:Svubr helbv qitdy gyx pref, mximuppvret ksncxaduah qzqk, tht zg utgsznk xdtbcy tjjtinamqt mx pgmvws mv jecqyn figup eplolr. Xn bzcy gu jkxfm tjuqjv, wvyr gnxwzpc kceekzfyiika bdukkuu ychdqrf qurg mo tgtwnes do zu wcfsbbr ooqrwxhwn. Mxke nksr kbmva zfnvk oi wmrbljoeplqob dk igqztvgwf slrsl jmuj thtnvx xnaorm dv kcytro cftpc wnllylkb. Weifhrfre ggrj yswrdmez qwfarjemf jav vcapjlwb, hjdz nz qixld kqs lpzifql echunajt myklem xykc ie iia hkgzyxh.
1:D:Yvsi xge Vfz: Nq Leytzn Prtok: Wvrf awp fat sumnq wdry iuc hf arjq, Rpwb wta dj enj.  Ahcq tjlm I'ua cfhymj xv uhftsv F bjmo zjpa miqmp vcx dyltr kfdx.  Yes ve wj bsi zd ornjro ndgur, K pupxw U dlae adpqkr kr pqoa Il yrp xrup dhi zsmuebotfrc vws In yntn dwooc Agr ccgsk qececzn.
2:E:Hello World!
2:E:Hello World!
3:E:Hello World!
3:E:Hello World!
1:D:Hruquwvxuvungoz, bq wbjea!

An example of the output produced:

********************************************************************************
Processing: Hello World!
User: 1
Direction: E
Encrypted Message: Wtsqz Yowbl!
********************************************************************************
Processing: Mvuge Eyygm!
User: 1
Direction: D
Encrypted Message: Hello World!
********************************************************************************
Processing: The quick brown fox jumps over the lazy dog!  
User: 2
Direction: E
Encrypted Message: Dai twypb zgsca keu ugvur jvnd jby tvox spr!  
********************************************************************************
Processing: Ccl wopqk lrlag vek pkxfl xysu uio cjjo nwk!
User: 2
Direction: D
Encrypted Message: The quick brown fox jumps over the lazy dog!
********************************************************************************
Processing: Svubr helbv qitdy gyx pref, mximuppvret ksncxaduah qzqk, tht zg utgsznk xdtbcy tjjtinamqt mx pgmvws mv jecqyn figup eplolr. Xn bzcy gu jkxfm tjuqjv, wvyr gnxwzpc kceekzfyiika bdukkuu ychdqrf qurg mo tgtwnes do zu wcfsbbr ooqrwxhwn. Mxke nksr kbmva zfnvk oi wmrbljoeplqob dk igqztvgwf slrsl jmuj thtnvx xnaorm dv kcytro cftpc wnllylkb. Weifhrfre ggrj yswrdmez qwfarjemf jav vcapjlwb, hjdz nz qixld kqs lpzifql echunajt myklem xykc ie iia hkgzyxh.
User: 3
Direction: D
Encrypted Message: Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
********************************************************************************
Processing: Yvsi xge Vfz: Nq Leytzn Prtok: Wvrf awp fat sumnq wdry iuc hf arjq, Rpwb wta dj enj.  Ahcq tjlm I'ua cfhymj xv uhftsv F bjmo zjpa miqmp vcx dyltr kfdx.  Yes ve wj bsi zd ornjro ndgur, K pupxw U dlae adpqkr kr pqoa Il yrp xrup dhi zsmuebotfrc vws In yntn dwooc Agr ccgsk qececzn.
User: 1
Direction: D
Encrypted Message: Fire and Ice: By Robert Frost: Some say the world will end in fire, Some say in ice.  From what I've tasted of desire I hold with those who favor fire.  But if it had to perish twice, I think I know enough of hate To say that for destruction ice Is also great And would suffice.
********************************************************************************
Processing: Hello World!
User: 2
Direction: E
Encrypted Message: Nweum Wjpom!
********************************************************************************
Processing: Hello World!
User: 2
Direction: E
Encrypted Message: Cxhnv Yhyso!
********************************************************************************
Processing: Hello World!
User: 3
Direction: E
Encrypted Message: Zxzfg Hxwgf!
********************************************************************************
Processing: Hello World!
User: 3
Direction: E
Encrypted Message: Mjskk Rbmqv!
********************************************************************************
Processing: Hruquwvxuvungoz, bq wbjea!
User: 1
Direction: D
Encrypted Message: Congratulations, it workd!
********************************************************************************

Final Key Report 
	For key 1
		Calls: 254
		Seed:  3381495176
	For key 2
		Calls: 90
		Seed:  1714247131
	For key 3
		Calls: 389
		Seed:  1635790872

Required Files

You should use additional structures/classes to make your code more readable.
Your final program should be called coder.cpp
You may want
- Makefile
- input.txt, the sample input file
- output.txt, the sample output file
Make sure you use good coding techniques
- A good functional decomposition
- Functions, so you have no repeated code
- Good identifier names
- Constants where appropriate
You can test your program by running the following lines:
- This assumes you have downloaded input.txt and output.txt
- If all is good, you should see no output.

Submission

Submit the assignment to the D2L folder Homework 3 by the due date.