11_pre_encrypted_inputs.cpp

// Copyright 2026 Niobium Microsystems, Inc.
// Licensed under the Apache License, Version 2.0.
// ============================================================================
//  11 — PRE-ENCRYPTED INPUTS  (the real production file shape)
// ============================================================================
//  💡 Real-world picture: a hospital encrypts patient records on its own
//  servers, then ships the SEALED FILES to a cloud running this kind of
//  analytics. The cloud computes on the encrypted bytes; it never holds a
//  decryption key. Even if the cloud is breached, attackers see only
//  encrypted blobs. This is how production FHE deployments look — and this
//  example is the shape they use, in 70 lines.
//
//  Example 10 moved inputs out of the source into a readable .txt file.
//  Real Niobium servers go one step further: inputs arrive on disk ALREADY
//  ENCRYPTED. The server only ever sees ciphertext bytes — a client (often
//  a different machine, sometimes a different organisation) did the
//  encryption earlier.
//
//  This example shows that exact shape:
//
//      * First run        — kit acts as the "client": encrypts the values,
//                            serialises each ciphertext to a .bin file under
//                            .runs/<backend>/.inputs/. The .bin location is
//                            per-backend because a ciphertext is tied to the
//                            keyset that encrypted it, and the kit uses
//                            independent keys for FHE_SIM vs FPGA.
//      * Every run after  — kit acts as the "server": loads each .bin file
//                            and hands it to the compiler with the FILENAME
//                            (3-arg tag_input), the way a production
//                            Niobium application does.
//
//  Because the .bin files live OUTSIDE the source tree, swapping them in or
//  out (or deleting and re-encrypting) does NOT trigger a recompile.
//
//  Run it:               ./run.sh 11_pre_encrypted_inputs        <- first run COMPILES on CPU
//  Run again:            ./run.sh 11_pre_encrypted_inputs        <- runs the cached program (RUNTIME)
//  Delete the .bin:      rm .runs/fhe-sim/.inputs/11_pre_encrypted_inputs.*.bin
//  Run again:            ./run.sh 11_pre_encrypted_inputs        <- re-encrypts, still RUNTIME
//  Compile + run once:   ./run.sh 11_pre_encrypted_inputs --full
//  Run on the FPGA:      ./run.sh 11_pre_encrypted_inputs --fpga
//                        (FPGA generates its own .bin under .runs/fpga/.inputs/)
// ============================================================================

#include "starter_kit.h"

using namespace niobium::starter;

int main(int argc, char** argv) {
    Session s(argc, argv, /*name=*/"11_pre_encrypted_inputs",
              /*mult_depth=*/1, /*rotation_indices=*/{1, 2, 4});

    // First run encrypts the literals and writes .bin files under the
    // per-backend .inputs/ (e.g. .runs/fhe-sim/.inputs/). Later runs load
    // those .bin files straight from disk. Either way, the compiler is told
    // the filename so it can reload on replay.
    auto a = s.encrypt_or_load_bin("a", {1, 2, 3, 4, 5, 6, 7, 8});
    auto b = s.encrypt_or_load_bin("b", {8, 7, 6, 5, 4, 3, 2, 1});

    s.compute([&] {
        auto cc = s.cc();
        auto prod = cc->EvalMult(a, b);             // element-wise product
        auto acc  = prod;
        for (int shift : {1, 2, 4})
            acc = cc->EvalAdd(acc, cc->EvalRotate(acc, shift));   // sum slots
        s.output("dot_product", acc);
    });

    s.print_and_verify();
    // For the shipped inputs (1..8 . 8..1) every slot ~= 120.
    return 0;
}

// ============================================================================
//  🧪 TRY THIS
// ============================================================================
//  - Delete the .bin files (`rm .runs/fhe-sim/.inputs/11_*.bin`) and run
//    again. The example re-encrypts fresh bytes; the compiled program is
//    reused — RUNTIME only.
//  - Open one of the .bin files: `xxd .runs/fhe-sim/.inputs/11_pre_encrypted_inputs.a.bin
//    | head`. What you see is the on-the-wire shape Niobium customers move
//    between their client and server — the accelerator never sees more
//    than this.
//  - Compare with example 10: same data-outside-source idea, but the data
//    is encrypted at rest. That's the only difference, and it's the entire
//    reason this pattern is production-appropriate.
//  - Revisit example 01 with the production cache:
//        ./run.sh 01_add --pre-encrypted --reset
//        ./run.sh 01_add --pre-encrypted --regen-input=a:100,200,300,400,500,600,700,800
//    The second invocation should hit RUNTIME (not COMPILE) even though
//    the data changed -- the production cache contract on an example
//    you've already learned. See README's Phase 2 section for context.
// ============================================================================