FAST Cipher (Zig Implementation)

A pure Zig implementation of the FAST (Format-preserving, Additive, Symmetric Translation) cipher. This library provides format-preserving encryption/decryption that maintains the same format (radix and length) between plaintext and ciphertext, making it ideal for encrypting sensitive data like credit card numbers, SSNs, or other structured data.

Usage

const std = @import("std");
const fast = @import("fast");

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    // Calculate recommended security parameters
    const radix = 10; // For decimal numbers (0-9)
    const word_length = 16; // For 16-digit numbers
    const params = try fast.calculateRecommendedParams(radix, word_length, 128);

    // Initialize cipher context with a 16-byte key
    const key = [_]u8{
        0x2B, 0x7E, 0x15, 0x16, 0x28, 0xAE, 0xD2, 0xA6,
        0xAB, 0xF7, 0x15, 0x88, 0x09, 0xCF, 0x4F, 0x3C,
    };

    var ctx = try fast.init(10, 256, allocator, &params, &key);
    defer {
        ctx.deinit();
        allocator.destroy(ctx);
    }

    // Encrypt data (using a tweak for domain separation)
    const tweak = [_]u8{ 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77 };
    const plaintext = [_]u8{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6 };
    var ciphertext: [16]u8 = undefined;

    try fast.encrypt(10, 256, ctx, &tweak, &plaintext, &ciphertext);

    // Decrypt data
    var recovered: [16]u8 = undefined;
    try fast.decrypt(10, 256, ctx, &tweak, &ciphertext, &recovered);

    // Verify roundtrip
    if (std.mem.eql(u8, &plaintext, &recovered)) {
        std.debug.print("Encryption/decryption successful!\n", .{});
    }
}