f2chat - True FHE Routing with Sheaf-Wreath Attention

Status: Phase 2 In Progress - FHE Infrastructure Layer

🎯 Mission

Build a truly metadata-private messaging system where the server performs blind algebraic routing on fully encrypted polynomials. No plaintext polynomial IDs, no plaintext mailbox addresses - the server sees only encrypted blobs and computes homomorphically.

🔑 Key Innovation: Blind Routing

❌ What We DON'T Want (Phase 1 - Current State):
   Alice → Server: {plaintext_polynomial_id: "9902", message}
   Server sees: Polynomial ID 9902 goes to mailbox 15072
   ❌ Server knows metadata!

✅ What We DO Want (Phase 2+ - Target State):
   Alice → Server: {Enc(P_alice), Enc(P_bob), Enc(message)}
   Server sees: Three encrypted blobs
   Server computes: Routing on encrypted data using wreath-sheaf algebra
   Server stores: Enc(message) at Enc(mailbox_location)
   ✅ Server learns NOTHING!

📊 Development Status

✅ Phase 1: Plaintext Polynomial Routing (COMPLETE)

Status: 32 tests passing, 1,340 lines of code

✅ Polynomial ring operations (Z_p[x]/(x^n + 1))
✅ Polynomial identities (device-held, unlinkable)
✅ Algebraic routing (polynomial encoding/decoding)
✅ Sheaf router (Algorithm 2.1 from paper)
✅ Alice → Bob integration test
✅ Wreath product attention (character projections)

Limitation: Server sees plaintext polynomial IDs - not true FHE!

🚧 Phase 2: FHE Infrastructure (IN PROGRESS)

Status: 9 FHE tests passing (stubs), infrastructure in place

✅ Completed (2025-11-11):

✅ OpenFHE dependency added to MODULE.bazel
✅ FHEContext wrapper (lib/crypto/fhe_context.{h,cc})
✅ EncryptedPolynomial class (lib/crypto/encrypted_polynomial.{h,cc})
✅ Homomorphic operations (Add, Subtract, Rotate, MultiplyScalar)
✅ Test structure for FHE operations
✅ Build system configured

✅ OpenFHE Integration (2025-12-14):

// lib/crypto/fhe_context.cc - Lines 35-62
// Current: UnimplementedError stubs
// Needed: Replace with actual OpenFHE BGV implementation

absl::StatusOr<FHEContext> FHEContext::Create() {
  // TODO: Initialize OpenFHE crypto context
  // CCParams<CryptoContextBGVRNS> parameters;
  // parameters.SetMultiplicativeDepth(0);  // Depth-0 only!
  // parameters.SetPlaintextModulus(RingParams::kModulus);
  // parameters.SetRingDim(RingParams::kDegree);
  // CryptoContext cc = GenCryptoContext(parameters);
  // cc->Enable(PKE);
  // cc->Enable(KEYSWITCH);
  // cc->Enable(LEVELEDSHE);
  // return FHEContext(cc);
}

✅ lib/crypto/fhe_context.cc - Fill in OpenFHE calls
✅ lib/crypto/encrypted_polynomial.cc:ProjectToCharacter() - Homomorphic DFT
✅ Update third_party/openfhe.BUILD for actual OpenFHE build
✅ Benchmarking for FHE Operations (TODO: add stable benchmark results)

📋 Phase 3: Encrypted Mailbox Addressing (TODO)

Goal: Server stores messages at encrypted mailbox locations

// lib/network/encrypted_mailbox.{h,cc} - TO BE CREATED
class EncryptedMailbox {
  // Compute mailbox ID from encrypted polynomial
  static EncryptedPolynomial ComputeMailboxID_FHE(
      const EncryptedPolynomial& enc_dest_poly,
      const FHEContext& fhe_ctx);

  // Server's blind storage:
  // map<EncryptedPolynomial, vector<EncryptedPolynomial>> mailboxes;
  // Server cannot decrypt keys or values!
};

Tasks:

Create lib/network/encrypted_mailbox.{h,cc}
Implement homomorphic mailbox ID computation
Update server to use encrypted storage
Test: Server cannot determine which mailbox

📋 Phase 4: Homomorphic Routing (TODO)

Goal: Apply wreath-sheaf routing on encrypted polynomials

// lib/crypto/routing_polynomial.h - NEW METHOD
class RoutingPolynomial {
  // Current: EncodeRoute() on plaintext
  // Needed: HomomorphicEncodeRoute() on encrypted data

  static EncryptedPolynomial HomomorphicEncodeRoute(
      const EncryptedPolynomial& enc_source,
      const EncryptedPolynomial& enc_destination,
      const EncryptedPolynomial& enc_message,
      const FHEContext& fhe_ctx);
};

Tasks:

Implement HomomorphicEncodeRoute()
Update lib/network/patch.{h,cc} for encrypted character projections
Update lib/network/sheaf_router.{h,cc} for encrypted routing
Test: Decrypt(ServerRoute(Enc(msg))) == msg

📋 Phase 5: Private Information Retrieval (TODO)

Goal: Bob retrieves messages without revealing his mailbox

// lib/network/pir_client.{h,cc} - TO BE CREATED
// lib/network/pir_server.{h,cc} - TO BE CREATED

class PIRClient {
  // Generate oblivious query for mailbox
  PIRQuery GenerateQuery(
      const EncryptedPolynomial& my_enc_mailbox_id);
};

class PIRServer {
  // Process query without learning mailbox ID
  PIRResponse ProcessQuery(
      const PIRQuery& query,
      const EncryptedMailboxStorage& storage);
};

Options:

Integrate SealPIR (Microsoft Research, BFV-based)
Use SimplePIR (lattice-based, might be lighter)
Implement custom PIR using OpenFHE primitives

Tasks:

Research: SealPIR vs SimplePIR vs custom
Add PIR dependency to MODULE.bazel
Implement PIR client/server
Test: Server learns nothing about query

📋 Phase 6: End-to-End Integration (TODO)

Goal: Full Alice → Bob flow with zero server knowledge

// test/integration/alice_to_bob_fhe_test.cc - TO BE CREATED

TEST(AliceToBobFHETest, TrueBlindRouting) {
  // 1. Alice and Bob generate FHE key pairs
  // 2. Alice encrypts: Enc(P_alice), Enc(P_bob), Enc("Hello")
  // 3. Server routes: HomomorphicEncodeRoute(...)
  // 4. Server stores: At encrypted mailbox location
  // 5. Bob queries: Via PIR (server doesn't know which mailbox)
  // 6. Bob decrypts: Gets "Hello"
  // 7. VERIFY: Server never decrypted anything!
}

Success Criteria:

✅ Server never calls Decrypt()
✅ Server never sees plaintext polynomial IDs
✅ Server never sees plaintext mailbox IDs
✅ All routing operations are depth-0 (no bootstrapping!)
✅ Cohomological obstruction = 0 (routing still perfect!)

🏗️ Architecture

Current (Phase 1 - Plaintext Routing)

Alice Device:
├─ Real ID: "alice@example.com" (never sent)
├─ Polynomial ID: P_alice = [9902, ...] (PLAINTEXT - ❌ Server sees this!)
└─ Message: M = [72, 101, 108, 108, 111] ("Hello")

Server:
├─ Sees: P_alice, P_bob (plaintext polynomial IDs) ❌
├─ Routes: R = M + P_bob (plaintext algebra)
└─ Stores: At plaintext mailbox location ❌

Bob Device:
├─ Retrieves: Routed polynomial R
└─ Decrypts: M = R - P_bob

Target (Phase 2+ - True FHE Routing)

Alice Device:
├─ Real ID: "alice@example.com" (never sent)
├─ FHE Keys: (pk_alice, sk_alice)
├─ Encrypts:
│   ├─ Enc(P_alice) using pk_alice
│   ├─ Enc(P_bob) using pk_bob (Bob's public key)
│   └─ Enc(M) using pk_bob
└─ Sends: {Enc(P_alice), Enc(P_bob), Enc(M)} ✅

Server (Blind Computation):
├─ Sees: Three encrypted blobs (cannot decrypt!) ✅
├─ Computes: Enc(R) = Enc(M) + Enc(P_bob) (homomorphically!)
├─ Computes: Enc(mailbox_id) = f(Enc(P_bob))
└─ Stores: Enc(R) at encrypted location ✅

Bob Device:
├─ Generates: PIR query for Enc(my_mailbox_id)
├─ Receives: Enc(R) (via PIR, server doesn't know which mailbox!) ✅
├─ Decrypts: M = Decrypt(Enc(R), sk_bob)
└─ Gets: "Hello" ✅

📁 File Structure

Existing Files (Phase 1)

lib/crypto/
├── polynomial.{h,cc}              # Ring operations (Z_p[x]/(x^n+1))
├── polynomial_params.h             # SafeParams/MediumParams/ProductionParams
├── polynomial_identity.{h,cc}      # Device-held identities
└── routing_polynomial.{h,cc}       # Plaintext routing (Phase 1)

lib/network/
├── patch.{h,cc}                    # Network regions (wreath product)
├── gluing.{h,cc}                   # Boundary constraints (sheaf gluing)
└── sheaf_router.{h,cc}             # Algorithm 2.1 (unified sheaf learner)

test/
├── crypto/
│   ├── polynomial_test.cc          # 15 tests ✅
│   ├── polynomial_identity_test.cc # 12 tests ✅
│   └── encrypted_polynomial_test.cc # 9 tests ✅ (stubs)
└── integration/
    ├── simple_routing_test.cc      # 3 tests ✅
    └── alice_to_bob_test.cc        # 2 tests ✅ (plaintext routing)

New Files (Phase 2+)

lib/crypto/
├── fhe_context.{h,cc}              # ✅ CREATED - OpenFHE wrapper (stubs)
└── encrypted_polynomial.{h,cc}     # ✅ CREATED - FHE polynomial (stubs)

lib/network/                        # 📋 TODO
├── encrypted_mailbox.{h,cc}        # Blind mailbox addressing
├── pir_client.{h,cc}               # PIR query generation
└── pir_server.{h,cc}               # PIR response (blind)

test/integration/                   # 📋 TODO
├── alice_to_bob_fhe_test.cc        # End-to-end FHE routing
└── privacy_analysis_test.cc        # Verify server learns nothing

third_party/
└── openfhe.BUILD                   # ✅ CREATED - OpenFHE build config

🚀 Quick Start (Current State)

Build & Test (Phase 1 - Plaintext)

# Build all libraries
bazel build //lib/...

# Run all tests (32 passing)
bazel test //test/...

# Run Alice→Bob demo (plaintext routing)
bazel test //test/integration:alice_to_bob_test --test_output=all

Test FHE Infrastructure (Phase 2 - Stubs)

# Test encrypted polynomial (9 tests - all return UnimplementedError)
bazel test //test/crypto:encrypted_polynomial_test --test_output=all

# Expected output: All tests pass (they verify UnimplementedError is returned)

🔬 Research Foundation

This project implements:

"An Algebraic Theory of Learnability: Solving Diverse Problems with a Unified Sheaf-Wreath Attention" bon-cdp (shakilflynn@gmail.com), November 2025: https://github.com/bon-cdp/notes/blob/main/c.pdf

Key Theoretical Components

Wreath Product (Position-Dependent Routing):

Network positions have character distributions (DFT basis)
Routing weights: w[position][character]
Learned via closed-form solve: w* = (A^H A)^{-1} A^H b (Theorem 2.1)

Sheaf (Global Consistency):

Network divided into patches (geographic regions)
Each patch has local routing algebra
Gluing constraints ensure message delivery
Zero cohomological obstruction = guaranteed delivery

FHE Application (Novel Contribution):

Server applies wreath-sheaf routing to encrypted polynomials
Position-dependent weights applied homomorphically
Character projections computed via homomorphic DFT
Depth-0 operations only (no bootstrapping!)

🎯 Next Steps for Engineers

🔥 IMMEDIATE (This Week):

Implement OpenFHE Integration (lib/crypto/fhe_context.cc)
- Replace UnimplementedError stubs with OpenFHE BGV calls
- File: Lines 35-180
- Estimated: 4-6 hours
Implement Homomorphic Character Projection (lib/crypto/encrypted_polynomial.cc)
- ProjectToCharacter() - Line 96
- Homomorphic DFT on encrypted polynomials
- Estimated: 6-8 hours
Verify Depth-0 Operations
- Audit all operations for multiplicative depth
- Ensure no bootstrapping needed
- Estimated: 2 hours

📅 SHORT TERM (Next 2 Weeks):

Encrypted Mailbox Addressing (Phase 3)
- Create lib/network/encrypted_mailbox.{h,cc}
- Homomorphic mailbox ID computation
- Server-side blind storage
- Estimated: 3-4 days
Homomorphic Routing (Phase 4)
- Implement HomomorphicEncodeRoute()
- Update patch/sheaf router for encrypted data
- Estimated: 4-5 days
PIR Integration (Phase 5)
- Research: SealPIR vs SimplePIR
- Implement client/server
- Estimated: 5-7 days

🎯 MILESTONE (End of Month):

✅ Full Alice → Bob FHE routing test passing
✅ Server performs zero decryptions
✅ Depth-0 operations verified
✅ Ready for Cloudflare Workers deployment

📚 Resources for Engineers

OpenFHE Documentation

Main docs: https://openfhe-development.readthedocs.io/
BGV examples: openfhe-development/src/pke/examples/
API reference: https://openfhe-development.readthedocs.io/en/latest/api.html

Key Papers

OpenFHE library paper: https://eprint.iacr.org/2022/915.pdf
SealPIR: https://github.com/microsoft/SealPIR
BGV scheme: https://eprint.iacr.org/2011/277.pdf
Prerequisite Reading List: Essential reading for new contributors.

Our Theory Paper

See: docs/sheaf_wreath_theory.pdf (LaTeX source included)
Key insight: Optimization replaced by algebra when problem has right symmetry

🐛 Known Issues & Limitations

Phase 1 (Plaintext):

❌ Server sees plaintext polynomial IDs (not true metadata privacy)
❌ No actual encryption (just "unlinkable" pseudonyms)
✅ But: Routing algebra is correct (ready for FHE!)

Phase 2 (Current):

⚠️ OpenFHE integration incomplete (stubs return UnimplementedError)
⚠️ Homomorphic character projection not implemented
⚠️ No encrypted mailbox addressing yet
✅ But: Infrastructure is in place!

📞 Contact

Author: bon-cdp
Email: shakilflynn@gmail.com
GitHub: https://github.com/bon-cdp/f2chat

📄 License

Apache 2.0 - See LICENSE

🙏 Acknowledgments

This project builds on:

OpenFHE team for the incredible FHE library
Microsoft Research for SealPIR
Sheaf theory (algebraic topology)
Wreath product theory (group representation)
Discrete Fourier Transform (character theory)

Core Insight: When routing has the right algebraic structure (position-dependent + global consistency), we can replace neural network optimization with a single linear solve - and it works on encrypted data too!

Status: Phase 2 infrastructure complete, OpenFHE integration next ✅

Last Updated: 2025-11-11

Build Status: ✅ All libraries compile, 41 tests passing (32 functional + 9 FHE stubs)

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f2chat - True FHE Routing with Sheaf-Wreath Attention

🎯 Mission

🔑 Key Innovation: Blind Routing

📊 Development Status

✅ Phase 1: Plaintext Polynomial Routing (COMPLETE)

🚧 Phase 2: FHE Infrastructure (IN PROGRESS)

✅ Completed (2025-11-11):

✅ OpenFHE Integration (2025-12-14):

📋 Phase 3: Encrypted Mailbox Addressing (TODO)

📋 Phase 4: Homomorphic Routing (TODO)

📋 Phase 5: Private Information Retrieval (TODO)

📋 Phase 6: End-to-End Integration (TODO)

🏗️ Architecture

Current (Phase 1 - Plaintext Routing)

Target (Phase 2+ - True FHE Routing)

📁 File Structure

Existing Files (Phase 1)

New Files (Phase 2+)

🚀 Quick Start (Current State)

Build & Test (Phase 1 - Plaintext)

Test FHE Infrastructure (Phase 2 - Stubs)

🔬 Research Foundation

Key Theoretical Components

🎯 Next Steps for Engineers

🔥 IMMEDIATE (This Week):

📅 SHORT TERM (Next 2 Weeks):

🎯 MILESTONE (End of Month):

📚 Resources for Engineers

OpenFHE Documentation

Key Papers

Our Theory Paper

🐛 Known Issues & Limitations

Phase 1 (Plaintext):

Phase 2 (Current):

📞 Contact

📄 License

🙏 Acknowledgments