Simple-Engima-Cipher-SV-Verilog HDL

Old project repo from 2019 Lab project Customised simple verilog HDL implementation of Engima cipher

Overview of the Enigma Machine

The Enigma machine consists of several components that work together to encrypt and decrypt messages: Plugboard: Swaps pairs of letters before and after the rotor system. Rotors: Apply a substitution (permutation) of the 26 letters, with positions that shift dynamically. Reflector: Reflects the signal back through the rotors, applying a fixed, involutory permutation.

The signal path through the machine is: input → plugboard → rotors (forward) → reflector → rotors (inverse) → plugboard → output. This symmetric process allows the same machine configuration to both encrypt and decrypt messages.

One-Hot Encoding

In this implementation, each letter of the A-Z alphabet is represented using one-hot encoding:

A = 000...001 (bit 0 = 1) B = 000...010 (bit 1 = 1) ... Z = 100...000 (bit 25 = 1)

This encoding scheme simplifies the implementation of permutations, as each operation can be modeled as a bit permutation, which is efficiently implementable in hardware.

Verilog Implementation

The implementation consists of several Verilog modules: Module Descriptions

Plugboard:

Input: 26-bit one-hot vector Output: 26-bit one-hot vector after permutation Implemented using assign statements to hardwire the swaps.

Rotor:

Inputs: 26-bit one-hot vector, 5-bit rotor position (0-25), direction (0 for forward, 1 for inverse) Output: 26-bit one-hot vector after permutation Implements the rotor's permutation, including shifts based on position.

Reflector:

Input: 26-bit one-hot vector Output: 26-bit one-hot vector after involutory permutation Implemented similarly to the plugboard with pairwise swaps.

Usage

To use this Enigma machine emulation: Set the rotor positions using the n1, n2, and n3 inputs (5-bit values representing positions 0 to 25). Provide the input letter as a 26-bit one-hot encoded vector. The output letter will be produced as a 26-bit one-hot encoded vector.

Eg:- For a specific configuration: Set rotor positions: n1 = 0, n2 = 0, n3 = 0 Input letter A: input_letter = 26'b000...001

The output will be the encrypted letter based on the machine's configuration.

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Verification with UVM (further changes required)

Interface | enigma_if.sv | Defines the signals connecting the testbench to the DUT.

Sequence Item | enigma_seq_item.sv | Encapsulates transaction data (input letter, rotor positions, output).

Sequence | enigma_sequence.sv | Generates a series of transactions with updated rotor positions.

Reference Model | enigma_ref_model.sv | Software model to predict expected outputs.

Driver | enigma_driver.sv | Drives input signals to the DUT based on sequence items.

Monitor | enigma_monitor.sv | Observes DUT outputs and sends transactions to the scoreboard.

Scoreboard | enigma_scoreboard.sv | Compares actual outputs with expected outputs from the reference model.

Agent | enigma_agent.sv | Groups driver, monitor, and sequencer for a cohesive interface.

Environment | enigma_env.sv | Contains agents and scoreboards for the verification environment.

Test | enigma_test.sv | Configures the environment and initiates the sequence.

Top Module | top.sv | Connects the DUT, interface, and testbench, starting the simulation.