🔬 Formal Verification for Meow-Encode

This directory contains formal specifications and proofs for Meow-Encode's security-critical components.

Overview

Tool	Purpose	Location	Status
TLA+/TLC	State machine model checking	`tla/`	✅ Complete
ProVerif	Symbolic protocol analysis (MEOW2-5)	`proverif/`	✅ Complete
Tamarin	Observational equivalence (MEOW3/4/5 PQ)	`tamarin/`	✅ Optional
Lean 4	Mathematical proofs	`lean/`	✅ Complete
Verus	Rust implementation proofs	`../crypto_core/`	✅ Complete

Protocol source of truth: docs/protocol.md

Quick Start

One-command verification:

make verify

Note: Tamarin runs only if tamarin-prover is installed. Local make verify will fail if it is missing; CI skips Tamarin unless installed.

TLA+ Model Checking (1-5 minutes)

cd /workspaces/meow-decoder/formal/tla

# Option 1: Direct Java (if you have tla2tools.jar)
java -jar tla2tools.jar -config MeowEncode.cfg MeowEncode.tla

# Option 2: Download TLC first
wget -q https://github.com/tlaplus/tlaplus/releases/download/v1.8.0/tla2tools.jar
java -jar tla2tools.jar -config MeowEncode.cfg MeowEncode.tla

# Option 3: Docker (no Java required)
docker run --rm -v $(pwd):/models toolsmiths/tla:latest tlc -config MeowEncode.cfg MeowEncode.tla

Expected output (success):

Model checking completed. No error has been found.
  States found: XXXX, distinct: XXXX

ProVerif Analysis (10-30 seconds)

cd /workspaces/meow-decoder/formal/proverif

# Option 1: Local ProVerif
eval $(opam env)
proverif meow_encode.pv

# Option 2: With HTML report
proverif -html output meow_encode.pv

# Option 3: Docker
docker run --rm -v $(pwd):/work proverif/proverif proverif /work/meow_encode.pv

Tamarin Equivalence (optional)

cd /workspaces/meow-decoder/formal/tamarin
./run.sh

You can also use Makefile shortcuts:

make formal-proverif
make formal-proverif-html

Expected output (success):

Query not attacker(real_secret[]) is true.
Query not attacker(real_password[]) is true.
...
RESULT All queries proved.

Verus Verification

cd /workspaces/meow-decoder/crypto_core

# Verify with Verus
verus src/lib.rs

Or run all formal checks at once:

make formal-all

Optimization Notes (January 2026)

The TLA+ model has been optimized for practical run times:

Parameter	Original	Optimized	Reason
`MaxFrames`	4	2	Fewer frame combinations
`MaxSessions`	3	1	Single session sufficient
`MaxNonces`	10	3	Still catches nonce reuse
`Passwords`	{1,2,3,4}	{1,2}	Real + duress only
`AttackerActionLimit`	none	3	Prevents state explosion

Result: ~10K-50K states in 1-5 minutes (vs. 10M+ states in hours)

The optimized config still verifies all 6 security invariants.

Security Properties Verified

1. TLA+ State Machine Properties

The TLA+ model verifies these safety invariants over all reachable states:

Invariant	Description
`DuressNeverOutputsReal`	Duress password → only decoy output
`NoOutputOnAuthFailure`	Auth failure → error state, no output
`ReplayNeverSucceeds`	Replayed frames always rejected
`NonceNeverReused`	Fresh nonce for each encryption
`TamperedFramesRejected`	Modified ciphertext → auth failure
`NoAuthBypass`	Output requires successful auth
`UnsealRequiresMatchingPCRs`	TPM unseal only with correct PCRs
`TamperPreventsUnseal`	Platform tampering prevents key access
`NoRealOutputWithoutUnsealedKey`	Real output requires unsealed hardware key
`SealedKeyNeverInChannel`	Hardware-sealed keys never appear in channel
`FailedUnsealBlocksDecrypt`	Failed unseal → no successful decryption
`KeyDerivationRequiresUnsealedOrSoftware`	Key derivation bound to hardware state
`AttackerCannotForgeUnseal`	Unseal is outside attacker's capabilities

2. ProVerif Protocol Properties

The ProVerif model proves these properties against a Dolev-Yao attacker:

Query	Description
`attacker(real_secret)`	Plaintext confidentiality
`attacker(real_password)`	Password never leaked
`DecoderOutputReal ==> EncoderEncrypted`	Payload authenticity
`ReplayRejected`	Replay attack resistance
`DuressCorrectness`	Duress mode works correctly
`NoAuthBypass`	No authentication bypass

3. Verus Implementation Properties

The Verus proofs verify these implementation-level invariants:

Property	Description
`nonce_uniqueness_invariant`	Nonce counter is strictly monotonic
`auth_then_output_invariant`	Plaintext only after GCM auth
`key_zeroization_invariant`	Key zeroed on drop
`no_nonce_reuse`	All encryptions use unique nonces

GuardedBuffer / SecureBox bounds proofs (verus_guarded_buffer.rs):

Property ID	Property	Lemma
GB-001	Guard-page layout: `data_ptr == mmap_base + page_size`	`lemma_guard_layout_established`
GB-002	Overflow prevention: index ≥ data_size hits upper PROT_NONE guard	`lemma_overflow_hits_upper_guard`
GB-003	Underflow prevention: `data_ptr - k` hits lower PROT_NONE guard	`lemma_underflow_hits_lower_guard`
GB-004	Data size correctness: `data_size() == size_of::<T>()`	`lemma_data_size_correctness`
GB-005	Total size ≥ data_size + 2 × page_size	`lemma_total_size_at_least_data_plus_two_guards`
GB-006	`data_region_size % page_size == 0` (mprotect alignment)	`lemma_data_region_page_aligned`
GB-007	Zeroize-on-drop: bytes set to 0 before `munmap`	`lemma_zeroize_erases_data`
GB-008	Valid access strictly within data region (not in either guard)	`theorem_guarded_buffer_safety`

Architecture

┌─────────────────────────────────────────────────────────────────────────┐
│                     FORMAL VERIFICATION STACK                           │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│  ┌─────────────────┐  ┌─────────────────┐  ┌─────────────────┐        │
│  │     TLA+/TLC    │  │    ProVerif     │  │      Verus      │        │
│  │  State Machine  │  │    Protocol     │  │  Implementation │        │
│  │     Model       │  │    Analysis     │  │     Proofs      │        │
│  └────────┬────────┘  └────────┬────────┘  └────────┬────────┘        │
│           │                    │                    │                  │
│           ▼                    ▼                    ▼                  │
│  ┌─────────────────────────────────────────────────────────────────┐  │
│  │                    VERIFIED PROPERTIES                          │  │
│  │                                                                 │  │
│  │  • Nonce uniqueness (TLA+, Verus)                              │  │
│  │  • Auth-then-output (TLA+, Verus)                              │  │
│  │  • Replay resistance (TLA+, ProVerif)                          │  │
│  │  • Tamper detection (TLA+, ProVerif)                           │  │
│  │  • Duress mode correctness (TLA+, ProVerif)                    │  │
│  │  • Key confidentiality (ProVerif)                              │  │
│  │  • Forward secrecy (ProVerif)                                  │  │
│  │  • Key zeroization (Verus)                                     │  │
│  └─────────────────────────────────────────────────────────────────┘  │
│                              │                                         │
│                              ▼                                         │
│  ┌─────────────────────────────────────────────────────────────────┐  │
│  │                     IMPLEMENTATION                              │  │
│  │                                                                 │  │
│  │  meow_decoder/crypto.py    ◄──── Python Implementation         │  │
│  │  rust_crypto/src/lib.rs    ◄──── Rust Backend                  │  │
│  │  crypto_core/src/*.rs      ◄──── Verified Crypto Core          │  │
│  └─────────────────────────────────────────────────────────────────┘  │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘

Threat Model Coverage

The formal verification covers the following threat model:

Attacker Capabilities (Dolev-Yao)

✅ Intercept - Attacker can read all network traffic
✅ Inject - Attacker can send arbitrary messages
✅ Replay - Attacker can replay old messages
✅ Reorder - Attacker can reorder messages
✅ Tamper - Attacker can modify messages (detected)
❌ Break crypto - Cannot break AES-256-GCM, Argon2id

Attack Scenarios Modeled

Attack	TLA+	ProVerif	Verus
Nonce reuse	✅	✅	✅
Replay attack	✅	✅	-
Frame tampering	✅	✅	-
Frame injection	✅	✅	-
Auth bypass	✅	✅	✅
Duress mode abuse	✅	✅	-
Key extraction	-	✅	✅
Forward secrecy break	-	✅	-
Guard page underflow	✅ (Tamarin symbolic)	-	✅ (GB-003, real `verus!{}`)
Buffer layout violation	-	-	✅ (GB-001, GB-005, GB-006)

Files

formal/
├── README.md                    # This file
├── tla/
│   ├── MeowEncode.tla          # TLA+ state machine specification
│   ├── MeowEncode.cfg          # TLC model checker configuration
│   └── README.md               # TLA+ documentation
├── proverif/
│   ├── meow_encode.pv          # ProVerif protocol specification
│   └── README.md               # ProVerif documentation
└── ../crypto_core/
    ├── Cargo.toml              # Rust crate configuration
    ├── src/lib.rs              # Crate entry point
    ├── src/aead_wrapper.rs     # AEAD wrapper (Verus annotations)
    ├── src/verus_guarded_buffer.rs  # ← NEW: real verus!{} bounds proofs (GB-001–GB-008)
    ├── src/verus_proofs.rs     # AEAD/nonce invariants (doc-comment annotations)
    ├── src/verus_kdf_proofs.rs # KDF invariants (doc-comment annotations)
    └── README.md               # Verus documentation

Verification Results

TLA+ (Expected Output)

All 3 models should report "No error has been found":

MeowEncode: ~300K distinct states (main protocol pipeline)
MeowFountain: ~44 states (fountain code properties)
MeowStreaming: ~57K states (streaming protocol)

Model checking completed. No error has been found.

ProVerif (Expected Output)

22 queries should report TRUE (critical security properties). 13 session-correspondence queries report FALSE — this is expected and documented (ProVerif overapproximates; these are not security violations).

Critical properties verified:

Confidentiality: attacker(real_secret) = FALSE
Password secrecy: attacker(real_password) = FALSE
Authentication: DecoderAuthenticated ==> EncoderStarted = TRUE
Duress safety: duress password never reveals real secret = TRUE
PQ secrecy: attacker(pq_shared_marker) = FALSE
Replay: ReplayAttempted ==> ReplayRejected = TRUE

Lean 4 (Expected Output)

lake build
# Exit 0, no errors

Sorry gate: no unapproved sorry keywords (documentation references excluded).

Cargo crypto_core (Expected Output)

cargo build --release
# Finished `release` profile

Verus (Expected Output)

verification results:: verified: 16 errors: 0
  nonce_uniqueness_invariant ... verified
  auth_then_output_invariant ... verified
  key_zeroization_invariant ... verified
  no_nonce_reuse ... verified
  lemma_guard_layout_established ... verified
  lemma_overflow_hits_upper_guard ... verified
  lemma_underflow_hits_lower_guard ... verified
  lemma_data_size_correctness ... verified
  lemma_total_size_at_least_data_plus_two_guards ... verified
  lemma_data_region_page_aligned ... verified
  lemma_zeroize_erases_data ... verified
  lemma_valid_access_in_data_region ... verified
  theorem_guarded_buffer_safety ... verified
  (+ 3 spec fn definitions)

Continuous Integration

Add to .github/workflows/formal-verification.yml:

name: Formal Verification

on: [push, pull_request]

jobs:
  tla-model-check:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Run TLC
        uses: docker://talex5/tlaplus
        with:
          args: tlc -config formal/tla/MeowEncode.cfg formal/tla/MeowEncode.tla

  proverif-analysis:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install ProVerif
        run: |
          sudo apt-get update
          sudo apt-get install -y proverif
      - name: Run ProVerif
        run: proverif formal/proverif/meow_encode.pv

  verus-verification:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install Verus
        run: |
          git clone https://github.com/verus-lang/verus
          cd verus && ./tools/get-z3.sh && ./tools/build.sh
      - name: Verify
        run: ./verus/target-verus/release/verus crypto_core/src/lib.rs

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🔬 Formal Verification for Meow-Encode

Overview

Quick Start

TLA+ Model Checking (1-5 minutes)

ProVerif Analysis (10-30 seconds)

Tamarin Equivalence (optional)

Verus Verification

Optimization Notes (January 2026)

Security Properties Verified

1. TLA+ State Machine Properties

2. ProVerif Protocol Properties

3. Verus Implementation Properties

Architecture

Threat Model Coverage

Attacker Capabilities (Dolev-Yao)

Attack Scenarios Modeled

Files

Verification Results

TLA+ (Expected Output)

ProVerif (Expected Output)

Lean 4 (Expected Output)

Cargo crypto_core (Expected Output)

Verus (Expected Output)

Continuous Integration

References

TLA+

ProVerif

Verus

Cryptographic Foundations

Contributing

License

FilesExpand file tree

README.md

Latest commit

History

README.md

File metadata and controls

🔬 Formal Verification for Meow-Encode

Overview

Quick Start

TLA+ Model Checking (1-5 minutes)

ProVerif Analysis (10-30 seconds)

Tamarin Equivalence (optional)

Verus Verification

Optimization Notes (January 2026)

Security Properties Verified

1. TLA+ State Machine Properties

2. ProVerif Protocol Properties

3. Verus Implementation Properties

Architecture

Threat Model Coverage

Attacker Capabilities (Dolev-Yao)

Attack Scenarios Modeled

Files

Verification Results

TLA+ (Expected Output)

ProVerif (Expected Output)

Lean 4 (Expected Output)

Cargo crypto_core (Expected Output)

Verus (Expected Output)

Continuous Integration

References

TLA+

ProVerif

Verus

Cryptographic Foundations

Contributing

License