HunterAdams.c

// lean implementation in c
// https://vanhunteradams.com/Enigma/Enigma.html
// C emulator for an Enigma Machine with 3 rotors
// Hunter Adams (vha3@cornell.edu)
//
// gcc eof.c -o eof
// 
#include <stdio.h>
#include <string.h>
// EXAMPLE SETTINGS FROM DIAGRAM FOUND ONLINE
// stecker: EBFJACUIHDLKMTOPRQXNGVZSYW - Arbitrary (though must be reciprocal)
// rotor 1: EKMFLGDQVZNTOWYHXUSPAIBRCJ - ROTOR I from online
// rotor 2: AJDKSIRUXBLHWTMCQGZNPYFVOE - ROTOR II from online
// rotor 3: BDFHJLCPRTXVZNYEIWGAKMUSQO - ROTOR III from online
// umkehrw: YRUHQSLDPXNGOKMIEBFZCWVJAT - Non-rotatable Umkehrwalze B from online
char STECKER [27]  = {4,0,3,6,22,23,14,1,25,20,1,25,0,6,0,0,1,25,5,20,12,0,3,21,0,23,0};
char ROTOR1  [27]  = {4,9,10,2,7,1,23,9,13,16,3,8,2,9,10,18,7,3,0,22,6,13,5,20,4,10,0};
char ROTOR2  [27]  = {0,8,1,7,14,3,11,13,15,18,1,22,10,6,24,13,0,15,7,20,21,3,9,24,16,5,0};
char ROTOR3  [27]  = {1,2,3,4,5,6,22,8,9,10,13,10,13,0,10,15,18,5,14,7,16,17,24,21,18,15,0};
char UMKEHR  [27]  = {24,16,18,4,12,13,5,22,7,14,3,21,2,23,24,19,14,10,13,6,8,1,25,12,2,20,0};
// variables to hold rotor positions
volatile int count1, count2, count3 ;
// Maximum size of the message that can be encoded (in character)
#define MAXINPUT 60

// sets rotor positions
void setRotor() {
    char value [5] ;
    printf("\nInput rotor positions (e.g. RNF): ") ;
    scanf("%s", value) ;
    count3=(value[0] - 'A');
    count2=(value[1] - 'A');
    count1=(value[2] - 'A');
}

// allows custom configuration of stecker, rotors, or umkehrwalze
void setElement(int classifier) {
    char peg = 'A' ;
    char c[27] ;
    char temp [27] ;
    int i ;

    switch (classifier)
    {
        case 0: 
            printf("\nInput stecker table: \n") ;
            break ;
        case 1: 
            printf("\nInput rotor 1 table: \n") ;
            break;
        case 2: 
            printf("\nInput rotor 2 table: \n") ;
            break;
        case 3: 
            printf("\nInput rotor 3 table: \n") ;
            break;
        case 4: 
            printf("\nInput umkehrwalze table: \n") ;
            break;
        default: printf("Invalid") ;
    }
    scanf("%s", c) ;

    while (peg <= 'Z') {
        int value = c[peg - 'A'] - peg ;
        if (value<0) value += ('Z' - 'A' + 1) ;

        switch (classifier)
        {
            case 0: 
                STECKER[peg-'A'] = value; 
                break;
            case 1: 
                ROTOR1[peg-'A'] = value; 
                break;
            case 2: 
                ROTOR2[peg-'A'] = value; 
                break;
            case 3: 
                ROTOR3[peg-'A'] = value; 
                break;
            case 4: 
                UMKEHR[peg-'A'] = value; 
                break;
            default: 
                printf("Invalid"); break; 
        }
        peg += 1 ;
    }

    switch (classifier)
        {
            case 0:
                printf("Stecker settings: \n") ;
                for (i=0; i<27; i++) {
                    printf("%d ", STECKER[i]) ;
                } 
                break;
            case 1: 
                printf("Rotor 1 settings: \n") ;
                for (i=0; i<27; i++) {
                    printf("%d ", ROTOR1[i]) ;
                } 
                break;
            case 2: 
                printf("Rotor 2 settings: \n") ;
                for (i=0; i<27; i++) {
                    printf("%d ", ROTOR2[i]) ;
                } 
                break;
            case 3: 
                printf("Rotor 3 settings: \n") ;
                for (i=0; i<27; i++) {
                    printf("%d ", ROTOR3[i]) ;
                } 
                break;
            case 4: 
                printf("Umkehrwalze settings: \n") ;
                for (i=0; i<27; i++) {
                    printf("%d ", UMKEHR[i]) ;
                } 
                break;
            default: 
                printf("Invalid"); break; 
        }
}

char forwardElement(char Element [27], char input, int countval) {
    // Get the index
    int index = input - 'A' + countval;
    // Make sure the index wraps at 25
    if (index>25) index = (index%26);
    // Update the character value with value at that index
    char output = (input + Element[index]);
    // Range check for values above Z, wrap to A
    if (output>90) output=((output%('Z'+1))+'A');
    // Return value
    return output ;
}


char reverseElement(char Element [27], char output, int countval) {
    // Start at char value 1 below A, outval 0, index 0
    char testval = 'A'-1 ;
    char outval = '0' ;
    int index = 0 ;
    // While the output value does not equal the desired output value
    while (outval != output) {
        // Increment the test character
        testval += 1 ;
        // Get the index of the character
        index = testval - 'A' + countval;
        // Make sure the index wraps at 25
        if (index>25) index = (index%26);
        // Update the test output value with the value at that index
        outval = (testval + Element[index]) ;
        // Range check for values above Z, wrap to A
        if (outval>90) outval=((outval%('Z'+1)) + 'A') ;
    }
    // Return the character that yielded desired output
    return testval ;
}


int main() {
    char c;
    char user_in[MAXINPUT] ;
    char user_out[MAXINPUT] ;
    int i ;
    printf("\n\nAt any time, press 'r' to set rotor configurations and 't' for a total reconfig.\n\n");

    setRotor() ;
    // Wait for keyboard entry
    printf("\nInput value (all caps no spaces): ");
    while(1) {
        // Get input
        scanf("%s", user_in) ;
        memset(user_out, 0, MAXINPUT) ;
        int j = 0 ;
        // Grab first character
        c = '0' ;
        while (j<strlen(user_in)) { 
            c = user_in[j] ;    
            if (c=='\r') break ;
            else if (c=='r') setRotor() ;
            else if (c=='t') {
                setElement(0);
                setElement(1);
                setElement(2);
                setElement(3);
                setElement(4);
                setRotor() ;
            }
            else {
                // COMMENT-IN THE PRINT STATEMENTS BELOW TO SEE
                // THE VALUE THAT IS ATTAINED IN EACH STEP OF THE
                // ENCODING CIRCUIT
                //
                // printf("\nInput value: %c", c);
                // Forward stecker
                char value2 = forwardElement(STECKER, c, 0) ;
                // printf("\nStecked value: "); putchar(value2) ;
                // Forward rotor 1
                char value3 = forwardElement(ROTOR1, value2, count1) ;
                // printf("\nRotorized value 1: "); putchar(value3) ;
                // Forward rotor 2
                char value4 = forwardElement(ROTOR2, value3, count2) ;
                // printf("\nRotorized value 2: "); putchar(value4) ;
                // Forward rotor 3
                char value5 = forwardElement(ROTOR3, value4, count3) ;
                // printf("\nRotorized value 3: "); putchar(value5) ;
                // Umkehrwalze
                char value6 = forwardElement(UMKEHR, value5, 0) ;
                // printf("\nUmkehrwalze value: "); putchar(value6) ;

                // print the rotor count1
                // printf("\nRotor count1: %d", count1) ;
                // print the rotor count2
                // printf("\nRotor count2: %d", count2) ;
                // print the rotor count3
                // printf("\nRotor count3: %d", count3) ;

                // Reverse Rotor 3
                char value7 = reverseElement(ROTOR3, value6, count3) ;
                // printf("\nRev. rotor value 3: "); putchar(value7) ;
                // Reverse Rotor 2
                char value8 = reverseElement(ROTOR2, value7, count2) ;
                // printf("\nRev. rotor value 2: "); putchar(value8) ;
                // Reverse Rotor 1
                char value9 = reverseElement(ROTOR1, value8, count1) ;
                // printf("\nRev. rotor value 1: "); putchar(value9) ;
                // Reverse stecker
                char value10 = reverseElement(STECKER, value9, 0) ;
                // printf("\nStecker Output: "); putchar(value10) ;

                user_out[j] = value10 ;

                // Iterate the rotor counters
                count1 = ((count1+1) % 26) ;
                if (count1==0) count2 = ((count2+1)%26) ;
                if ((count1==0)&&(count2==0)) count3 = ((count3+1)%26) ;
            }
            j += 1 ;
        }

        printf("\n\n%s\n\n", user_out) ;

        // Get a new input value
        printf("\n\nInput value (all caps no spaces): ");
    }
}