CS计算机代考程序代写 data structure compiler Java ER algorithm junit Project 1: The Enigma

Project 1: The Enigma

Introduction
This programming assignment is intended to exercise a few useful data structures and an object-based

view of a programming problem. There is some background reading, but the necessary program is not (or

rather need not be) terribly big. The conceptual video walkthrough is located here, which we HIGHLY

RECOMMEND watching.

We will be grading largely on whether you manage to get your program to work (according to our tests). In

addition, we will be looking at your own tests (which you should be sure to turn in as well). While we have

supplied a few unit tests and some simple integration tests and testing utilities, the tests in the skeleton

are entirely inadequate for testing your program. There is also a stylistic component: the grading

machinery require that your program pass a mechanized style check (style61b), which mainly checks for

formatting and the presence of comments in the proper places. See the Style Guide for a brief description

of the style rules. You may change any of the code we’ve provided, as long as the resulting program

works according to the specifications here.

To obtain the skeleton files (and set up an initial entry for your project in the repository), you can use the

command sequence

git fetch shared
git merge shared/proj1 -m “Get proj1 skeleton”

from your Git working directory. Should we update the skeleton, you can use exactly the same sequence

to update your project with the same changes.

Background
You may have heard of the Enigma machines that Germany used during World War II to encrypt its

military communications. If you have not, I recommend you read the wikipedia page on them, or similar

resource, especially the part about design and operation. This video shows what one version of the

machine looked like and how it operated. This project involves building a simulator for a generalized

version of this machine (which itself had several versions.) Your program will take descriptions of possible

initial configurations of the machine and messages to encode or decode (the Enigma algorithms were

reciprocal, meaning that encryption is its own inverse operation.)

The Enigmas effect a substitution cipher on the letters of a message. That is, at any given time, the

machine performs a permutation—a one-to-one mapping—of the alphabet onto itself. The alphabet

consists solely of the 26 letters in one case (there were various conventions for spaces and punctuation).

Plain substitution ciphers are easy to break (you’ve probably seen puzzles in newspapers that consist of

breaking such ciphers). The Enigma, however, implements a progressive substitution, different for each

subsequent letter of the message. This made decryption considerably more difficult.

The device consists of a simple mechanical system of (partially) interchangeable rotors (Walzen) that sit

side-by-side on a shaft and make electrical contact with each other. Most of these rotors have 26 contacts

on both sides, which are wired together internally to effect a permutation of signals coming in from one

side onto the contacts on the other (and the inverse permutation when going in the reverse direction). To

the left of the rotors, one could select one of a set of reflectors (Umkehrwalzen), with contacts on their

right sides only, and wired to connect half of those contacts to the other half. A signal starting from the

rightmost rotor enters through one of the 26 possible contacts, flows through wires in the rotors,

“bounces” off the reflector, and then comes back through the same rotors (in reverse) by a different route,

always ending up being permuted to a letter position different from where it started; that is, the

permutation was always a derangement. (This was a significant cryptographic weakness, as it turned out.

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

https://inst.eecs.berkeley.edu/~cs61b/fa21/docs/style-guide.html
https://en.wikipedia.org/wiki/Enigma_machine

https://inst.eecs.berkeley.edu/~cs61b/fa21/index.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/about.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/staff.html
https://beacon.datastructur.es/
https://inst.eecs.berkeley.edu/~cs61b/fa21/resources.html
https://piazza.com/class/jkx2gta66436jq

It doesn’t really do a would-be code-breaker any good to know that some letters in an encrypted message

might be the same as the those in the plaintext if he doesn’t know which ones. But it does a great deal of

good to be able to eliminate possible decryptions because some of their letters are the same as in the

plaintext.)

Each rotor and each reflector implements a different permutation, and the overall effect depends on their

configuration: which rotors and reflector are used, what order they are placed in the machine, and which

rotational position they are initially set to. This configuration is the first part of the secret key used to

encrypt or decrypt a message. The reflector’s permutation was designed to be a derangement, so each

letter was mapped to a different letter, which guaranteed that the letter inputted into the enigma machine

would be different than the one outputted. In what follows, we’ll refer to the selected reflector and rotors in

a machine’s configuration as 1 through N, with 1 being the reflector, and N the rightmost rotor. In our

simulator, N will be a configuration parameter. In actual Enigma machines, it was fixed for any given

model (the Kreigsmarine (Navy) used (four rotors and reflector) and the Wehrmacht used .)

The overall permutation changes with each successive letter because some rotors rotate after encrypting

a letter. Each rotor has a circular ratchet on its right side and an “alphabet ring” on its left side that fits

over the ratchet of the rotor to its left. Before a letter of a message is translated, a spring-loaded pawl

(lever)—one to the right of each rotating rotor—tries to engage the ratchet on the right side of its rotor and

thus rotate its rotor by one position, changing the permutation performed by the rotor. Thus, pawls always

try to engage with the ratchet of their own rotor. The lever on the rightmost rotor (N) always succeeds, so

that rotor N (the “fast” rotor) rotates one position before each character. The pawls pushing the other

rotors, however, are normally blocked from engaging their rotors by the alphabet ring on the left side of

the rotor to their right. This interactive website provides a good visualization of how signals travel through

the rotors and how messages are encrypted. DISCLAIMER: This visualizer does not depict the underlying

details of how rotors rotate. It’s just a tool that may help your understanding of how the electrical signals

propagate through the system.

This ring usually holds the pawl away from its own ratchet, preventing the rotor wheel to its left from

moving. However, the rings have notches in them (either one or two in the original Enigma machines),

and when the pawl is positioned over a notch in the ring for the rotor to its right, it slips through to its own

rotor and pushes it forward. A “feature” of the design called “double stepping” (corrected in other versions

of the Enigma, since it reduced the period of the cipher) is that when a pawl is in a notch, it also moves

the notch itself and the rotor the notch is connected to. Since the notch for rotor is connected to rotor ,

when the pawl of rotor slips through into the notch for rotor , rotors on both sides of the pawl move

(so rotor and rotor move).

The effect of advancing a wheel is to change where on the wheel any given signal enters or leaves. When

a wheel is in its ‘A’ setting in the machine, then a signal that arrives from the right at, say, the ‘C’ position,

goes into the ‘C’ contact on the wheel. Likewise, a signal that leaves the wheel from its left ‘C’ contact

exits at the ‘C’ position. When the wheel is rotated by one to its ‘B’ setting, a signal that arrives at the ‘C’

position goes instead into the ‘D’ contact on the wheel, and a signal that leaves through the ‘D’ contact

does so at the ‘C’ position. It’s easier to calculate if we use numbers 0–25 rather than letters (‘A’ is 0, ‘B’ is

1, etc.). Then, when the wheel is in its setting, a signal entering at the position enters the

contact on the wheel, and a signal exiting through the contact does so at the

position. For example, Figure 1 shows one of the rotors from the real Enigma machines

(called rotor “I”) and the effect of moving from its ‘A’ to its ‘B’ setting.

N = 5 N = 4

i i

i − 1 i

k p

p + k mod 26 c

c − k mod 26

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

https://observablehq.com/@tmcw/enigma-machine
https://inst.eecs.berkeley.edu/~cs61b/fa21/index.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/about.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/staff.html
https://beacon.datastructur.es/
https://inst.eecs.berkeley.edu/~cs61b/fa21/resources.html
https://piazza.com/class/jkx2gta66436jq

Figure 1. Permutations performed by a rotor in its ‘A’ and ‘B’ settings. The italicized alphabets

at the top and bottom indicate the letters corresponding to the positions around the rotor. The

inner alphabets indicate the positions along the rotor itself. The rotor depicted was designated

‘I’ in the original Enigma machine used by the German military.

Let’s illustrate with a much simplified version. Suppose our alphabet has only the letters A-C and we have

four rotors (numbered 1-4) each of which has one notch on its ring at the C position. Suppose also that

there are 3 pawls, one for each of rotors 2-4. We will still refer to these as pawls 2-4, to maintain that pawl

belongs to rotor . There is no pawl for rotor 1, which will therefore not rotate. We’ll start with the rotors

set at AAAA. The next 19 positions are as follows:

AAAB AAAC AABA AABB AABC AACA ABAB ABAC
ABBA ABBB ABBC ABCA ACAB ACAC ACBA ACBB
ACBC ACCA AAAB

As you can see,

Rotor 4, the fast rotor, advances each time, pushed by pawl 4. Rotor 4 has no rotor to its right, so

there isn’t a ring blocking it from engaging with its ratchet.

Rotor 3 advances whenever Rotor 4 is at C. Rotor 4 has a notch at C, so pawl 3 can engage with

the corresponding ratchet (the ratchet belonging to Rotor 3) and advance Rotor 3 by pushing on its

ratchet. This would also rotate Rotor 4, since pawl 3 contacts its ratchet through the notch of Rotor

4, and therefore pushes the side of the notch when it moves. However, since Rotor 4 always rotates

anyway (because pawl 4 is always unblocked), this doesn’t really change anything.

Rotor 2 advances whenever Rotor 3 is at C, pushed by pawl 2. Rotor 3 has a notch at C, so pawl 2

slips into the notch and engages with its ratchet (the ratchet belonging to Rotor 2). Rotor 3 also

advances when it is at C, because when pawl 2 is engaged through Rotor 3’s notch it will push

against that notch when it moves, moving Rotor 3, as well as moving Rotor 2 by pushing on Rotor

2’s ratchet.

Since there is no pawl 1, double-stepping does not occur, so Rotor 2 (unlike Rotor 3) does not

advance just because it is at C.

Rotor 1 never changes, since there is no pawl on either side of it.

Each rotor can only advance at most one position per keypress.

So the advancement of the rotors, while similar to that of the wheels of an odometer, is not quite the

same. If it were, then the next position after AACA would be AACB, rather than ABAB. Also, it would take

27 steps to return to the initial configuration instead of 18.

The contacts on the rightmost rotor’s right side connect with stationary input and output contacts, which

run to keys that, when pressed, direct current to the contact from a battery or, when not pressed, direct

i i

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

current back from the contact to a light bulb indicating a letter of the alphabet. Since a letter never

encrypts or decrypts to itself after going back and forth through the rotors, the to and from directions never

conflict.

The German Navy used a machine with 12 rotors and five slots for them:

Eight rotors labeled with roman numerals I–VIII, of which three will be used in any given

configuration as the rightmost rotors,

Two additional non-moving rotors (Zusatzwalzen) labeled “Beta” and “Gamma”, of which one will be

used in any configuration, as the fourth-from-right rotor, and

Two reflectors (Umkehrwalzen), labeled ‘B’ and ‘C’, of which one will be used in any given

configuration as the leftmost rotor.

Given just this equipment, there are 614,175,744 possible configurations (or keys):

Two possible reflectors, times

Two possible rotors in the fourth position, times

choices for the rightmost three rotors and their ordering, times

possible initial rotational settings for the rightmost four rotors (each reflector had only one

possible position.).

Especially by today’s standards, this is not a large key size (less than 30 bits). To make things more

difficult for code-breakers, therefore, the Enigma incorporated a plugboard (Steckerbrett) between the

keyboard and the rightmost wheel. It acted as a non-moving, configurable rotor. The operator could

choose any set of disjoint pairs of letters by means of cables placed between them on the plugboard.

Each selected pair would then be swapped going into the machine from the keyboard and coming out into

the indicator lights. Thus, if the operator connected (“steckered”) the letters A and P, then P would be

substituted for each A typed and vice versa. Likewise, if an ingoing letter was encrypted to P by the other

rotors, it would display as A, and letters decrypted as A would display as P.

Describing Permutations
Since the rotors and the plugboard implement permutations, we’ll need a standard way to describe them.

We could simply have a table showing each letter and what it maps to, but we’ll use a more compact

notation known as cycle representation. The idea is that any permutation of a set may be described as a

set of cyclic permutations. For example, the notation

(AELTPHQXRU) (BKNW) (CMOY) (DFG) (IV) (JZ) (S)

describes the permutation in Figure 1. It describes seven cycles:

A maps to E, E to L, L to T, …, R to U, and U back to A.

B maps to K, K to N, N to W, and W back to B.

C maps to M, M to O, O to Y, and Y back to C.

D maps to F, F to G, and G back to D.

I maps to V and V back to I.

J maps to Z and Z back to J.

S maps to itself.

The inverse permutation just reverses these cycles:

U maps to R, R to X, …, E to A, and A back to U.

…

S maps to itself.

Each letter appears in one and only one cycle, so the mapping is unambiguous. As a shorthand, we’ll say

that if a letter is left out of all cycles, it maps to itself (so that we could have left off “(S)” In the example

8!/(8 − 3)! = 336

26
4

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

above.)

Figure 2 shows the permutations corresponding to the rotors used in the German Navy’s Enigma

machine.

Rotor Permutation (as cycles) Notch
Rotor I (AELTPHQXRU) (BKNW) (CMOY) (DFG) (IV) (JZ) (S) Q

Rotor II (FIXVYOMW) (CDKLHUP) (ESZ) (BJ) (GR) (NT) (A) (Q) E

Rotor III (ABDHPEJT) (CFLVMZOYQIRWUKXSG) (N) V

Rotor IV (AEPLIYWCOXMRFZBSTGJQNH) (DV) (KU) J

Rotor V (AVOLDRWFIUQ)(BZKSMNHYC) (EGTJPX) Z

Rotor VI (AJQDVLEOZWIYTS) (CGMNHFUX) (BPRK) Z and
M

Rotor VII (ANOUPFRIMBZTLWKSVEGCJYDHXQ) Z and
M

Rotor VIII (AFLSETWUNDHOZVICQ) (BKJ) (GXY) (MPR) Z and
M

Rotor Beta (ALBEVFCYODJWUGNMQTZSKPR) (HIX)

Rotor
Gamma

(AFNIRLBSQWVXGUZDKMTPCOYJHE)

Reflector B (AE) (BN) (CK) (DQ) (FU) (GY) (HW) (IJ) (LO) (MP) (RX)
(SZ) (TV)

Reflector C (AR) (BD) (CO) (EJ) (FN) (GT) (HK) (IV) (LM) (PW) (QZ)
(SX) (UY)

Figure 2. The rotors used in the Naval Enigma, showing the permutations they implement and

the point(s) at which there are notches that allow their left neighbor rotor to advance. Thus,

when Rotor I is at ‘Q’ and the machine advances, the rotor to the left of Rotor I will advance.

The Beta and Gamma rotors and the reflectors do not rotate. The reflectors shown here are

the “thin” versions of the reflectors used in the naval M4 Enigma machine. The B reflector

together with the Beta rotor in the ‘A’ position had the same effect as the usual (“thick”) B

reflector in the older three-rotor M3 Enigma machine (likewise the C reflector with the Gamma

rotor). This allowed the M4 to encrypt and decrypt messages to and from M3 Enigmas.

Source: Tony Sale’s pages.

Example
As an example of a translation, consider the set of rotors from Figure 2, and suppose that

The rotors in positions 1–5 are, respectively, B, Beta, III, IV, and I.

The rotors in positions 2–5 are currently at positions A, X, L, E, respectively.

In the plugboard, the letter pair ‘Y’ and ‘F’ and the letter pair ‘Z’ and ‘H’ are both interchanged.

We input the letter ‘Y’, which causes the following steps:

1. The pawls all move. This causes rotor 5 to advance from E to F. The other two pawls are not over

notches, so rotors 3 and 4 do not move.

2. The letter ‘Y’ enters the plugboard and is converted to ‘F’.

3. The letter ‘F’ enters the right side of rotor 5 (an I rotor) at position 5, since ‘F’ is the 5th letter of the

alphabet numbering from 0. Since the current setting of rotor 5 is ‘F’, the signal enters the rotor at

position , but hits contact , or ‘K’.

4. According to Figure 2, rotor I converts ‘K’ to ‘N’ (letter number 13). Because the setting of rotor I is

‘F’, however, the signal actually comes out at letter position (‘I’).

5. The ‘I’ signal from rotor 5 now goes into the right side of rotor 4. Since rotor 4 is a IV rotor and is in

the ‘L’ (or 11) setting, the ‘I’ enters at contact (‘T’), and is translated to ‘G’ (6), which

5 5 + 5 = 10

13 − 5 = 8

8 + 11 = 19

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

http://www.codesandciphers.org.uk/enigma/rotorspec.htm
https://inst.eecs.berkeley.edu/~cs61b/fa21/index.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/about.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/staff.html
https://beacon.datastructur.es/
https://inst.eecs.berkeley.edu/~cs61b/fa21/resources.html
https://piazza.com/class/jkx2gta66436jq

comes out at position , the fifth letter from the end of the alphabet (‘V’).

6. The ‘V’ from rotor 4 goes now to the right side of rotor 3, a III rotor in setting ‘X’ (23). The signal

enters the rotor at contact (‘S’), is translated to ‘G’ (6), which exits at

position (‘J’).

7. Rotor 2 (Beta) is in position ‘A’, and thus translates ‘J’ to ‘W’.

8. Rotor 1 (B) converts the ‘W’ to ‘H’ and bounces it back to the left side of rotor 2.

9. Rotor 2 (Beta in the ‘A’ position) converts ‘H’ on its left to ‘X’ (23) on its right.

10. The ‘X’ from rotor 2 now goes into the (‘U’) contact on the left side of

rotor 3 (III in setting ‘X’), and is converted to ‘W’ (22), which comes out at position

(‘Z’) on the right side of rotor 3.

11. ‘Z’ now enters the left side of rotor 4 (IV in setting ‘L’) at (‘K’), and is

translated to ‘U’ (20), which comes out at position (‘J’) on the right side of rotor 4.

12. The ‘J’ from rotor 4 enters the left side of rotor 5 (I at setting ‘F’) at contact (‘O’), is

translated to ‘M’ (12), and comes out at position (‘H’) on the right side of rotor 5.

13. Finally,the letter ‘H’ is converted to ‘Z’ by the plugboard.

Therefore, ‘Y’ is converted to ‘Z’.

After a total of 12 characters are converted, the rotor settings will have become ‘AXLQ’. Just before the

next character is converted, rotor 5 will advance to ‘R’ and, since its notch is at position ‘Q’, rotor 4 will

advance to ‘M’, so that the rotor configuration will be ‘AXMR’ before the 13th character is converted. After

an additional 597 characters have been converted, the configuration will be ‘AXIQ’. The character after

that will advance rotor 5 to ‘R’ and rotor 4 to ‘J’, giving ‘AXJR’. The next character will advance 5 to ‘S’,

and, since rotor IV’s notch is at ‘J’, rotor 3 will advance to ‘Y’. Also, as rotor 3’s pawl advances rotor 3, it

also moves the notch on rotor 4, advancing rotor 4 to ‘K’, so that the configuration goes from ‘AXJR’ to

‘AYKS’. Rotor 3 in this case has a notch at ‘V’, but since rotor 2 has no pawl, rotor 3’s notch never has any

effect.

Input and Output
To run your program on the command line, first compile all of your files with

javac -g -Xlint:unchecked enigma/*.java

or, if you have it, just use

make

After compiling, you can use the command

java -ea enigma.Main [configuration file] [input file] [output file]

to run your program. The configuration file contains descriptions of the machine and the available rotors.

The data are in free format. That is, they consist of strings of non-whitespace characters separated by

arbitrary whitespace (spaces, tabs, and newlines), so that indentation, spacing, and line breaks are

irrelevant. Each file has the following contents:

A string of the form where the are non-blank ASCII characters other than “*”, “(”

and “)”. This is the alphabet of the machine, giving both the character set and the ordering of the

characters around a rotor. For the examples in this document, we use just the upper-case alphabet

(as did the Enigma machines), but your solution must deal with general alphabets. In the following,

we will generally refer to the characters in this alphabet as “letters”, even when they include digits,

punctuation, or other symbols.

Two integer numerals, (Updated 9/26), where is the number of rotor slots (including

the reflector) and is the number of pawls—that is, the number of rotors that move. The moving

rotors and their pawls are all to the right of any non-moving ones.

6 − 11 = −5 = 21 mod 26

21 + 23 = 44 = 18 mod 26

6 − 23 = −17 = 9 mod 26

23 + 23 = 46 = 20 mod 26

22 − 23 = −1 = 25 mod 26

25 + 11 = 36 = 10 mod 26

20 − 11 = 9

9 + 5 = 14

12 − 5 = 7

⋯C1C2 Cn Ci

S > P > 0 S

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

Any number of rotor descriptors. Each has the following components (separated by whitespace):

A name containing any non-blank characters other than parentheses.

One of the characters R, N, or M, indicating that the rotor is a reflector, a non-moving rotor, or

a moving rotor, respectively. Non-moving rotors can only be used in positions through

and moving rotors in positions through .

Immediately after the M for a moving rotor come(s) the letter(s) at which there is a notch on

the rotor’s ring (no space between M and these letters).

The cycles of the permutation, using the notation discussed above.

For example, the German Naval Enigma machine might be described with this configuration file (see

Figure 2):

ABCDEFGHIJKLMNOPQRSTUVWXYZ
5 3
I MQ (AELTPHQXRU) (BKNW) (CMOY) (DFG) (IV) (JZ) (S)
II ME (FIXVYOMW) (CDKLHUP) (ESZ) (BJ) (GR) (NT) (A) (Q)
III MV (ABDHPEJT) (CFLVMZOYQIRWUKXSG) (N)
IV MJ (AEPLIYWCOXMRFZBSTGJQNH) (DV) (KU)
V MZ (AVOLDRWFIUQ)(BZKSMNHYC) (EGTJPX)
VI MZM (AJQDVLEOZWIYTS) (CGMNHFUX) (BPRK)
VII MZM (ANOUPFRIMBZTLWKSVEGCJYDHXQ)
VIII MZM (AFLSETWUNDHOZVICQ) (BKJ) (GXY) (MPR)
Beta N (ALBEVFCYODJWUGNMQTZSKPR) (HIX)
Gamma N (AFNIRLBSQWVXGUZDKMTPCOYJHE)
B R (AE) (BN) (CK) (DQ) (FU) (GY) (HW) (IJ) (LO) (MP)
(RX) (SZ) (TV)
C R (AR) (BD) (CO) (EJ) (FN) (GT) (HK) (IV) (LM) (PW)
(QZ) (SX) (UY)

The input file to your program will consist of a sequence of messages to decode, each preceded by a line

giving the initial settings. Given the configuration file above, a settings line looks like this:

* B Beta III IV I AXLE (YF) (ZH)

The asterisk must appear in the first column. Other items on the line may be separated from each other

by tabs and blanks; adjacent items that are rotor names or consist entirely of letters from the alphabet

must be so separated. This particular example means that the rotors used are reflector B, and rotors

Beta, III, IV, and I, with rotor I in the rightmost, or fast, slot. The remaining parenthesized items indicate

that the letter pair Y and F and the pair Z and M are steckered (swapped going in from the keyboard and

going out to the lights).

In general for this particular configuration, rotor 1 is always the reflector; rotor 2 is Beta or Gamma, and

each of 3-5 is one of rotors I-VIII. A rotor may not be repeated. The four letters of the following word

(AXLE in the example) give the initial positions of rotors 2-5, respectively (i.e., not including the reflector).

Any number of steckered pairs may follow (including none).

After each settings line comes a message on any number of lines. Each line of a message consists only

of letters (here meaning characters from the specified alphabet), spaces, and tabs (0 or more). The

program should ignore the blanks and tabs. The end of message is indicated either by the end of the input

or by a new configuration line (distinguished by its leading asterisk). The machine is not reset between

lines, but continues stepping from where it left off on the previous message line. Because the Enigma is a

reciprocal cipher, a given translation may either be a decryption or encryption; you don’t have to worry

about which, since the process is the same in any case.

Output the translation for each message line in groups of five characters, separated by a space (the last

group may have fewer characters, depending on the message length). Figure 3 contains an example that

shows an encryption followed by a decryption of the encrypted message. Since we have yet to cover the

details of File I/O, you will be provided the File IO machinery for this project.

Input | Output
* B Beta III IV I AXLE (HQ) (EX) (IP) (TR) (BY) | QVPQS OKOIL PUBKJ ZPISF XDW
FROM HIS SHOULDER HIAWATHA | BHCNS CXNUO AATZX SRCFY DGU
TOOK THE CAMERA OF ROSEWOOD | FLPNX GXIXT YJUJR CAUGE UNCFM
MADE OF SLIDING FOLDING ROSEWOOD | WJFGK CIIRG XODJG VCGPQ OH
NEATLY PUT IT ALL TOGETHER | ALWEB UHTZM OXIIV XUEFP RPR
IN ITS CASE IT LAY COMPACTLY | KCGVP FPYKI KITLB URVGT SFU
FOLDED INTO NEARLY NOTHING | SMBNK FRIIM PDOFJ VTTUG RZM
BUT HE OPENED OUT THE HINGES | UVCYL FDZPG IBXRE WXUEB ZQJO

2 S − P

S − P + 1 S

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

PUSHED AND PULLED THE JOINTS AND HINGES TILL IT LOOKED ALL SQUARES AND OBLONGS LIKE A COMPLICATED FIGURE IN THE SECOND BOOK OF EUCLID * B Beta III IV I QVPQS OKOIL PUBKJ ZPISF XDW BHCNS CXNUO AATZX SRCFY DGU FLPNX GXIXT YJUJR CAUGE UNCFM KUF WJFGK CIIRG XODJG VCGPQ OH ALWEB UHTZM OXIIV XUEFP RPR KCGVP FPYKI KITLB URVGT SFU SMBNK FRIIM PDOFJ VTTUG RZM UVCYL FDZPG IBXRE WXUEB ZQJO YMHIP GRRE GOHET UXDTW LCMMW AVNVJ VH OUFAN TQACK KTOZZ RDABQ NNVPO IEFQA FS VVICV UDUER EYNPF FMNBJ VGQ | YMHIP GRRE
| GOHET UXDTW LCMMW AVNVJ VH
| OUFAN TQACK
| KTOZZ RDABQ NNVPO IEFQA FS
| VVICV UDUER EYNPF FMNBJ VGQ
|
| FROMH ISSHO ULDER HIAWA THA
AXLE (HQ) (EX) (IP) (TR) (BY) | TOOKT HECAM ERAOF ROSEW OOD
| MADEO FSLID INGFO LDING ROSEW
| NEATL YPUTI TALLT OGETH ER
| INITS CASEI TLAYC OMPAC TLY
| FOLDE DINTO NEARL YNOTH ING
| BUTHE OPENE DOUTT HEHIN GES
| PUSHE DANDP ULLED THEJO INTS
| ANDHI NGES
| TILLI TLOOK EDALL SQUAR ES
| ANDOB LONGS
| LIKEA COMPL ICATE DFIGU RE
| INTHE SECON DBOOK OFEUC LID
|
|

Figure 3. Sample input and output (using the Naval cipher).

Editing Main
Within Main.java, you will be working with Scanners. We recommend that before you tackle this portion

of the project you do homework 4, as there will substantial practice on that assignment. Inside of

Main.java you will deal with a substantial amount of input handling (involving both valid and invalid

inputs). Do not assume that all of your inputs will be well-formed and do your best to make sure that you

handle all cases where the input is not what is expected.

In addition to this, in Main.java, you will need to print output in a way that matches our sample output

file. The Unix convention is that every line ends with a newline (we say that newline is a line terminator

rather than a line separator), so make sure that your output file also includes a newline at the end. If your

output seems exactly the same as the grader’s, but you are failing a test, chances are that there is a

newline error.

Handling Errors
You can see a number of opportunities for input errors:

The configuration file may have the wrong format.

The input might not start with a setting.

The setting line can contain the wrong number of arguments.

The rotors might be misnamed.

A rotor might be repeated in the setting line.

The first rotor might not be a reflector.

The initial positions string might be the wrong length or contain characters not in the alphabet.

Messages containing characters from outside the alphabet.

A significant amount of a program will typically be devoted to detecting such errors, and taking corrective

action. In our case, the main program is set up in such a way that the only corrective action needed is to

throw an EnigmaException with an explanatory message. The existing code in the main program will

catch this exception, print its message, and exit with a standard Unix error indication. The skeleton

supplies a simple static utility method, error, which provides a convenient way to create error

exceptions. There are examples of its use in the skeleton.

Testing

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

The directory testing contains the scripts test-correct and test-error for testing the execution of

enigma.Main.

bash test-correct F1.in F2.in … will run the program for each of the message files F1.in, F2.in

…, comparing the results to the corresponding output files F1.out, F2.out, …. The configuration files

used are F1.conf, F2.conf, …. However, if any of these is missing, the file default.conf (from the

same directory as the input file) is used instead.

bash test-error F1.in F2.in … will run the program for each of the message files F1.in, F2.in …,

checking that the program reports at least one error in each case. The configuration files are as for

test-correct.

This needs to be run in your proj1 directory, with paths to test-correct and input files. For example:

bash testing/test-correct testing/correct/trivial1.in

The tests we’ve supplied are nowhere near adequate to test your program, so you will need to generate

your own integration tests as well as unit tests (we will check to see that you make an effort to test).

Writing Unit Tests & Integration Tests
A (non-conclusive) video guide on how to test is given here.

Note about the video guide: The point in the spec in Vid #3 was: “A rotor might be repeated in the setting

line.” Upon checking the AG tests, it turns out this line was meant for the .in file and your solution DOES

NOT need to account for repetitions in the .conf file. To be clear, .conf would not be tested for

repetitions so it is okay if your code can’t handle that.

We recommend you write unit tests for each class you write. We have provided you the files

PermutationTest.java and MovingRotorTest.java, but if you create new files outside of that, make

sure to link it in UnitTest.java. Lab 6 (coming soon) will provide resources on how to go about writing

unit tests and integration tests for Enigma, and will specifically walk you through writing tests for

Permutation and using staff-enigma to help generate your own integration tests.

Running Enigma in IntelliJ
As touched upon above, you can run your program on the command line. In this section, we will cover

how to run Enigma on IntelliJ with input and output files.

Navigate to the Main class in your project. Try clicking the green play button next to the main method in

Main, and select ‘Run Main.main()’. If you haven’t previously inputted arguments, you should see an error

like this:

We got this error because we haven’t passed in any arguments to the program! Notice that between 1 and

3 arguments can be passed in:

ARGS[0] is the name of a configuration file.

ARGS[1] names an input file containing messages.

ARGS[2] names an output file for processed messages.

At the top right hand side of your screen, you should see a dropdown menu now labeled Main. You should

click the dropdown and select ‘Edit Configurations…’

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

A window should pop up, and you should be able to enter in your arguments in the Program Arguments

bar. For this example, create a file called riptide.in in your testing/correct/ directory with the following

contents:

* B Beta I II III AAAA (TD) (KC) (JZ)
I WAS SCARED OF CODING IN JAVA
I WAS SCARED OF USING GIT
AND STARTING ALL THESE PROJECTS
COMPILER KEEPS GETTING MAD AT ME
NOW MY PROJECT ONLY RUNS IN MY DREAMS
OH OH ALL THESE MERGE CONFLICTS

If you’ve copied the file into your directory, you should be able to refer to your default.conf

configuration file and the riptide.in file. Make sure you specify the correct path to your files, with

respect to your Working Directory.

This is equivalent to specifying the program arguments as such:

java -ea enigma.Main [configuration file] [input file] [output file]

Now run Main.main(). We haven’t specified an output file, so you should see the output of your machine

in standard output. If you’re wondering, you’ve just encrypted a verse in the Summer 2017 CS61BL

Musical!

As a reference, you should see output like below (if you have completed much of the project). You’re

welcome to make a new output file and add that to your program arguments if you prefer.

We encourage you to write more of your own input and configuration files and test them as above. We

expect that you have added adequate unit tests and additional integration tests beyond those provided in

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

the skeleton.

Comparing with the Staff Solution
You can run tests on the staff solution by ssh-ing into your instructional account and running staff-

enigma . In order to redirect your output to a certain file you can add >>

filename at the end of each command, for example, staff-enigma >>

file1.out

To compare your files with the staff files, you can run sdiff file1 file2 or use an online diffchecker.

Extra Credit
If after completing your solution, you are for some reason hankering for more, you can, for 2 points of

extra credit, implement the last missing piece of the Enigma: the ring setting (Ringstellung). The alphabet

rings are so called because they are marked with the letters of the alphabet. It is these letters that appear

in the panel of the machine and indicate the current settings of the rotors. In the real Enigma, the rotors’

rings are adjustable. Think of the positions on a rotor as being numbered from 0, with 0 being the usual

position of the first letter of the alphabet on the ring. The ring can be turned to make any letter of the

alphabet correspond to that 0 position instead. If, for example, we have the usual upper-case alphabet,

and we set the ring of rotor III so that “B” is at the 0 position, then when the setting of that rotor is “B”, the

rotor will convert “J” to “T”, just as that rotor would normally translate “J” when in the “A” position.

Likewise, when at the “D” setting, it would translate as it normally would in the “C” setting.

Besides affecting the meaning of the rotor settings, the alphabet ring also carries the notches that allow

adjacent rotors to move. The III rotor, for example, has a notch at its “V” position. Normally, this comes

into play when the rotor is at its 21 position, since “V” is letter number 21 in the alphabet (numbering from

0). But when the alphabet ring is set so that “B” is at the 0 position, the notch occurs at the rotor’s 20

position.

To specify the ring setting, we add an additional string to the configuration line. For example, the line

* B Beta III IV I AXLE AAAA (BQ)

is the same as what we have been writing as

* B Beta III IV I AXLE (BQ)

That “AAAA” is the (optional) ring setting; for the usual alphabet, “AAAA” is the default setting. The

reflector (B) does not have an adjustable ring. The line

* B Beta III IV I AXLE BEAR (BQ)

says that the ring setting of the Beta rotor is “B”, the III rotor is “E”, IV is “A”, and I is “R”.

Your solution must still handle configuration lines without the ring setting.

Office Hours
For office hours debugging, we will stick to the following norms.

Course staff will spend at most ~10 minutes per student.

You must provide a useful description of your question, or the staff may choose to help another

person on the queue that does have one. Please preface your question with one of the

following 4 sections of the project: Permutations, Rotors, Machine, Main.

Your code must be well documented, including all methods you write, according to the style guide.

This is to minimize time spent verbally explaining what each method does.

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

https://www.diffchecker.com/
https://inst.eecs.berkeley.edu/~cs61b/fa21/index.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/about.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/staff.html
https://beacon.datastructur.es/
https://inst.eecs.berkeley.edu/~cs61b/fa21/resources.html
https://piazza.com/class/jkx2gta66436jq

Your code must be well organized and explainable. It is not a good use of your time or the TAs’ time

to try to find bugs in something that is disorganized and brittle. When we do provide debugging help,

it may be at a high level, where we suggest ways to reorganize your code in order to make clarity

and debugging easier.

If your question is for debugging help, you must be prepared to explain the error that is being

caused and have a test or input that can easily reproduce the bug for ease of debugging. If you

come to us saying something does not work, but have not written any tests or attempted to use the

debugger, we will not help you. Saying “I am failing test X” is not an explanation of the error that is

being caused. Where is it happening? What is the type of error? What led up to this? If you have a

debugging question, we will often ask you to submit a Gitbug rather than helping you in OH.

We will attempt to group students in office hours to reduce queue time. This means you should talk

to your surrounding neighbors and discuss possible approaches to each other’s bugs. You may not

get 1-on-1 debugging help at peak office hours times, but a high level plan of attack to identify and

narrow down the causes of your bug.

Checkpoint
By Monday, September 27, (9/27) at 11:59PM you must have completed the following in order to receive

2 points of extra credit.

1. Completed this quiz. You do not need to answer all questions correctly to receive full points, but you

should understand all the correct answers by the time you start coding. Feel free to ask any

questions you have about the quiz in office hours, but please refrain from revealing answers on

Piazza. The quiz is out of 1.3 points, but the extra credit points earned will be calculated as

max(your score, 1) so you can only earn one extra credit point for the quiz.

2. Have made some changes to the Permutations and Rotors parts of the project. This involves

significant edits being made in 3 of 5 (Updated 9/26) of the following files. This will earn you .5 an

extra credit point:

– `Permutations.java`
– `Rotor.java`
– `MovingRotor.java`
– `Reflector.java`
– `FixedRotor.java`

3. All of your code compiles. This will earn you .5 an extra credit point.

Submit to the checkpoint by committing it and tagging it as follows (note the tag is proj1a not proj1):

git tag proj1a-0 # Or proj1a-1, etc.
git push
git push –tags

What To Turn In
1. You should commit and push your completed project with the commit you want graded tagged and

tags pushed. Your submission should contain no debugging print statements upon submission.

2. Your program must pass the style checker with 0 errors. This includes adequately commenting all

methods. Use the command make style to run style check locally on all your files. Do not use the

IntelliJ stylechecker plugin.

3. You should have added adequate unit tests, both for the provided methods and any additional

methods you write. We say “adequate” because the amount may change depending on how many

additional methods you write or how rigorous each test is. You will know if your test suite is

adequate.

4. You should have added additional integration tests beyond those provided in the skeleton. Again,

the exact number is not specified, but we recommend having enough that you feel confident that

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

https://inst.eecs.berkeley.edu/~cs61b/fa21/cgi-bin/gitbug.cgi/index
https://www.gradescope.com/courses/285455/assignments/1486892
https://inst.eecs.berkeley.edu/~cs61b/fa21/index.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/about.html
https://inst.eecs.berkeley.edu/~cs61b/fa21/staff.html
https://beacon.datastructur.es/
https://inst.eecs.berkeley.edu/~cs61b/fa21/resources.html
https://piazza.com/class/jkx2gta66436jq

passing them means your program is correct.

Grading Details
Project 1 is due Thursday, 10/7 at 11:59 PM PT. The project is worth 28 points. Your score on gradescope

will be your final score for the assignment.

You will be able to submit to the Project 1 gradescpe autograder starting on Thursday, 9/23. The tests

included in the skeleton code are not the full suite of tests that will be run on your submission. The

intention is that you write tests for your code, and do not rely on autograder submissions to debug

problems. To encourage this, you will only be able to submit to the autograder once every 3 hours, and

limited error output will be displayed.

Starting 10/4, the autograder will show more information about why you are failing some tests, and what

the tests that you are failing contain. Starting 10/7, you will be able to submit to the grader 4 times every

hour, and in the last 2 hours before the deadline, there are no restrictions on submissions to account for

any last minute issues such as wifi or git problems.

As a warning, you will not be able to complete the project if you wait to start or test your code until full

autograder logs are available 3 days before the deadline. You should plan to start early, and write your

own extensive tests for this assignment.

Advice
First, get started immediately, of course. Don’t just jump in and code, though. Make sure you understand

the specifications (which have their subtleties) and plan out how you’re going to meet them. Read the

skeleton code and understand the design. Figure out how to break this problem down into small pieces,

and how to implement and test them one piece at a time. Know in detail how you’re going to do something

before writing a line of Java code for it. In particular, take some time to understand how the rotors work,

and especially how the rotor position modifies the permutation.

Don’t allow things to remain mysterious to you, or they’ll surely bite you at some point. You don’t have to

use any of the skeleton code we’ve provided as long as the command java enigma.Main works as

specified. However, if you find yourself throwing something away because you don’t understand it, STOP!

You’re allowing yourself to be mystified by something that is intended to be simple.

There is a fair amount of string-hacking involved. The Java library can help you. Look at the

documentation of String, HashMap, ArrayList, and Scanner in the on-line Java library documentation.

We particularly invite you to consider the constructors and the methods

From String From ArrayList From HashMap From Scanner
charAt add get next

replaceAll get put nextInt

split size hasNext()

startsWith hasNext(…)

substring nextLine

toUpper

trim

indexOf

Be creatively lazy. Feel free to browse the Java library for useful stuff, even if you haven’t seen it in class.

If you find yourself writing:

if (rotor.equals(“I”) {
if (c == ‘A’)
e = ‘E’;
else if (c == ‘B’)
e = ‘K’;
…
}

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

or something equally hideous, STOP! you are doing something wrong!

You can write JUnit tests and integration tests (see the testing directory) before you write a line of code.

Be particularly careful to include tests that at one point caused your program to fail (regression tests) so

that you can be sure you don’t backslide when you make further changes. There’s no reason you can’t

have tests that you fail, by the way; they’ll serve to remind you of things you still need to do.

Use the git repository. Frequently commit your work so that you’ll never have to reconstruct too much if

your files somehow vanish mysteriously.

Above all, it is always fair to ask for help and advice. We don’t ever want to hear about how you’ve been

beating your head against the wall over some problem for hours. If you can’t make progress, don’t waste

your time guessing or bleeding: ask. If nobody’s available to ask, do something else (or get some sleep).

A Plan of Attack some TAs found useful was

Write code for Alphabet for a more generic alphabet.

Write tests for permutations, then all code for Permutations.

Write tests for rotors, then all code for the various Rotor classes, going from least specific to most.

Write code for Machine, creating tests as you account for various edge cases or error cases while

coding.

Finally, finish Main, again adding tests for various edge cases as you go.

Common Bugs
1. % in Java is remainder, and has different behavior from what you might expect with negative

numbers. Please see the provided method wrap for modular conversions, or see what the body of

wrap does and replicate this if you prefer to use your own methods.

Navigation

Introduction

Background

Describing Permutations

Example

Input and Output

Editing Main

Handling Errors

Testing

Writing Unit Tests &
Integration Tests

Running Enigma in IntelliJ

Comparing with the Staff
Solution

Extra Credit

Office Hours

Checkpoint

What To Turn In

Grading Details

Advice

Common Bugs

Main Course Info Staff Beacon Resources Piazza

Related Posts