January 30, 2006

1. Team M1Enigma MachineAdithya Attawar (M11)Shilpi Chakrabarti (M12)Zavo Gabriel (M13)Mike Sokolsky (M14) January 30, 2006 Original mechanical design revisited, High-level software simulation, Architecture flowcharts

2. Status • Finished: • Design selections • Block diagram for processes • High-level implementation in C • To Do: • Behavioral Verilog (almost done) • Schematic • Layout • Testing • Simulation

3. Functional Description • Enigma Operation Revisited

4. Enigma Operation: Rotors & Reflector • 26 spring-loaded contacts on each side • Set to an arbitrary initial position for each message • Each rotor has unique internal wiring to perform letter swaps • Rightmost rotor steps one notch with each keystroke, the others every 26, 262, etc. • Reflector does not move; hard-wired; swaps letters and ‘reflects’ signal back through rotors

5. Enigma Operation: Steckerboard • Manually wired and changed daily • Daily settings specified in codebooks given to operators • Matched letter pairs (A-J, J-A) • Increased number of possible machine configurations by 26*24*22*… = ~1013

6. Design Decisions • Revised entire system architecture • Modular design – able to add/revise components without changing basic architecture • Implement steckerboard, rotors, reflector using memories • Address: (Character + Wheel Position)%26 • Value in cell: New character for next swap • Will need to implement a 5-bit modulo-26 adder • Serial input of initial rotor settings/order

7. Steckerboard Memory • 26x5-bit cells • Programmable by user on startup • Stores information about swaps • newChar = stecker[currentChar] • Swaps MUST BEmatched pairs: • If stecker[A] = ‘G’ then stecker[G] = ‘A’

8. Rotor and Reflector Memory • Same basic idea as Steckerboard • 8 “rotors”: • 26x5-bit cells • Swaps are NOT matched pairs • 1 “reflector” • 26x5-bit cells • Swaps MUST BE matched pairs • Differences: • Not programmable: bits in memory are permanently set during manufacturing • Swap pairs unique to each wheel • Control logic specifies how many “rotors” used, in what “position,” and in what order

9. I-Reg Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

10. I-Reg Character Input Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

11. I-Reg Steckerboard Swap & Increment Wheels Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

12. I-Reg Calculate Rotor Swap Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

13. I-Reg Store New Character from Rotor Swap Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

14. I-Reg Calculate Reflector Swap Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

15. I-Reg Store New Character from Reflector Swap Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

16. I-Reg Calculate Reverse Rotor Swap Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

17. I-Reg Store New Character from Reverse Rotor Swap Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

18. Steckerboard Swap & Output Encrypted Character I-Reg Plug Input Wheel Select N-Reg C-Reg ROM 232 X 5bit 5-bit %26 Adder RAM 26 X5bit Wheel Pos + 13 % 26 O-Reg

19. Implementation in C (snippet) • while((ch_in=(char)getchar())!=10){ // take input until <ENTER> • c_reg = (unsigned short) ch_in - 97; // ASCII 'a' is value 97 so correct to a=0 • if(c_reg>25) • exit(0); • if((wheel_pos[wheel_order[0]] = (wheel_pos[wheel_order[0]]+1)%26)==0) // rotate wheels • if((wheel_pos[wheel_order[1]] = (wheel_pos[wheel_order[1]]+1)%26)==0) • if((wheel_pos[wheel_order[2]] = (wheel_pos[wheel_order[2]]+1)%26)==0) • if((wheel_pos[wheel_order[3]] = (wheel_pos[wheel_order[3]]+1)%26)==0) • if((wheel_pos[wheel_order[4]] = (wheel_pos[wheel_order[4]]+1)%26)==0) • if((wheel_pos[wheel_order[5]] = (wheel_pos[wheel_order[5]]+1)%26)==0) • if((wheel_pos[wheel_order[6]] = (wheel_pos[wheel_order[6]]+1)%26)==0) • if((wheel_pos[wheel_order[7]] = (wheel_pos[wheel_order[7]]+1)%26)==0); • //printf("%d %d ",wheel_pos[wheel_order[0]],wheel_pos[wheel_order[1]]); • if(use_stecker) // initial stecker use • c_reg = stecker[c_reg]; • for(i=0;i<num_wheels;i++) { // step through wheels • c_reg = wheel_settings[wheel_order[i]][(c_reg+wheel_pos[wheel_order[i]])%26]; • if(DEBUG) • printf("%c ",(char)(c_reg+97)); • } • if(reflect){ // if we're reflecting, which it looks like you have to do for it to work • c_reg = reflector[c_reg]; // look up new value in reflector • if(DEBUG) • printf("%c ",(char)(c_reg+97)); • for(i=num_wheels-1;i>=0;i--){ // now go through backwards, find the location in the wheel that holds • j=0; // the value of c_reg, and save the location into c_reg • while(wheel_settings[wheel_order[i]][(j+wheel_pos[wheel_order[i]])%26]!=c_reg) • j++; • c_reg = j; • if(DEBUG) • printf("%c ",(char)(c_reg+97));

20. Implementation in C • Fully simulates an Enigma with up to 8 rotors, a reflector, and a steckerboard • Sample output • 3 rotors: order 1-2-0, setting F-H-J • 5 stecker pairings: AP, CN, HS, KT, VX cmu-163055:~/Documents/Programs/Enigma mvs$ ./enigma helloworld (Input string from user) xoserrykrb (Encoded output) cmu-163055:~/Documents/Programs/Enigma mvs$ ./enigma xoserrykrb (Input string – the encoded text back in) helloworld (Output – encrypt and decrypt are the same)

21. Problems & Questions • How to make it more secure? • Variable rotor increments? • Must be some function of input character to preserve symmetrical encrypt/decrypt • Otherwise you lose your message!