212 lines
8.5 KiB
Markdown
212 lines
8.5 KiB
Markdown
# Security Policy — Zupt v2.0.0
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## Reporting Vulnerabilities
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**Be free to report vulnerabilities. For high-risk send an email.**
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Email: **ethicalhacker@riseup.net**
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Include: description, reproduction steps, impact assessment.
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Response within 48 hours. Fix within 30 days for critical issues.
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---
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## Encryption Modes
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| Mode | CLI Flag | Algorithm | PQ-Safe? | Use Case |
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|------|----------|-----------|----------|----------|
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| Password | `-p` | PBKDF2-SHA256 → AES-256-CTR + HMAC-SHA256 | **No** | Short-term backups, personal use |
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| PQ Hybrid | `--pq` | ML-KEM-768 + X25519 → AES-256-CTR + HMAC-SHA256 | **Yes** | Long-term archives, high-value data |
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| None | (default) | No encryption (compression only) | N/A | Non-sensitive data |
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**Password mode (`-p`) is NOT quantum-safe.** For protection against "harvest now, decrypt later" quantum attacks, use `--pq` mode.
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---
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## Cryptographic Algorithms
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| Component | Algorithm | Standard | Key Size | Security Level |
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|-----------|-----------|----------|----------|---------------|
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| Symmetric encryption | AES-256-CTR | FIPS 197 | 256-bit | 128-bit post-quantum (Grover) |
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| Authentication | HMAC-SHA256 | RFC 2104 | 256-bit | 128-bit post-quantum (Grover) |
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| Password KDF | PBKDF2-SHA256 | RFC 8018 | 600K iterations | Password-dependent |
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| Post-quantum KEM | ML-KEM-768 | FIPS 203 | 1184B pk / 2400B sk | NIST Level 3 |
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| Classical KEM | X25519 | RFC 7748 | 32B scalar | ~128-bit classical |
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| Hybrid KDF | SHA3-512 | FIPS 202 | 512-bit output | Secure if either KEM holds |
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| Integrity | XXH64 | xxHash spec | 64-bit checksum | Non-cryptographic |
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| Hashing | SHA3-256, SHA3-512 | FIPS 202 | 256/512-bit | Standard |
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| Random | OS CSPRNG | getrandom(2) / RtlGenRandom | N/A | Hard fail if unavailable |
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---
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## Security Architecture
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### Per-Block Authenticated Encryption
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```
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For each data block (sequence 0, 1, 2, ...):
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nonce = base_nonce XOR pad_le(block_seq, 8) [16 bytes]
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ciphertext = AES-256-CTR(enc_key, nonce, plaintext)
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mac = HMAC-SHA256(mac_key, nonce ‖ ciphertext) [32 bytes]
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stored = nonce ‖ ciphertext ‖ mac
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```
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### Encrypt-then-MAC
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HMAC is computed over `nonce ‖ ciphertext` and verified **before** any decryption. This prevents:
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- Chosen-ciphertext attacks
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- Padding oracle attacks
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- Processing of tampered data
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### Hybrid Post-Quantum KEM
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```
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Encapsulation:
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ML-KEM-768.Encaps(pk) → ml_ct[1088], ml_ss[32]
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eph_sk ← CSPRNG(32)
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eph_pk = X25519(eph_sk, basepoint)
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x25519_ss = X25519(eph_sk, recipient_pk)
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hybrid_ikm = ml_ss XOR x25519_ss
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archive_key = SHA3-512(hybrid_ikm ‖ ml_ct ‖ eph_pk ‖ "ZUPT-HYBRID-v1")
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enc_key = archive_key[0:32]
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mac_key = archive_key[32:64]
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```
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**Security model:** Secure if EITHER ML-KEM-768 (post-quantum, NIST Level 3) OR X25519 (classical, ~128-bit) remains unbroken. Both must be compromised simultaneously to recover the archive key. Same approach as Signal (PQXDH), Apple iMessage (PQ3), and OpenSSH 9.0+.
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---
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## Constant-Time Guarantees
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### Jasmin-Verified (assembly linked into binary)
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| Function | Purpose | Proof |
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|----------|---------|-------|
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| `zupt_mac_verify_ct` | HMAC comparison (32 bytes) | Jasmin type system: no branch on diff value |
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| `zupt_ct_select_32` | ML-KEM FO implicit rejection | Jasmin type system: no branch on cond value |
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These functions are compiled from Jasmin source to x86-64 assembly. The Jasmin compiler enforces that no secret-typed variable flows into branch conditions or memory addresses. This guarantee holds at the machine code level — no C compiler optimization can introduce timing leaks.
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### C Constant-Time (branchless, compiler-dependent)
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| Function | Method | Risk |
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|----------|--------|------|
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| X25519 `fe_cswap` | Masked XOR (`mask & (a ^ b)`) | Low — branchless but compiler may optimize |
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| ML-KEM NTT/basemul | Montgomery reduction (no branches) | Low |
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| ML-KEM CBD sampling | Bitwise operations only | Low |
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| Key wipe (`zupt_secure_wipe`) | `explicit_bzero` / volatile | Low |
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### NOT Constant-Time (documented risks)
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| Function | Risk | Mitigation |
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|----------|------|------------|
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| AES-256 block encrypt | **HIGH** on shared hardware — S-box table lookups leak via cache timing | Jasmin AES-NI path planned; do not use on multi-tenant VMs |
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| SHA-256 | Low — table constants are public, not indexed by secret data | Accepted |
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---
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## Threat Model
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### What Zupt Protects
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| Asset | Protection |
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|-------|-----------|
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| File contents | AES-256-CTR encryption |
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| File names, sizes, structure | Encrypted in central index block |
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| Archive integrity | Per-block XXH64 + HMAC-SHA256 |
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| Against stolen backups | AES-256 requires key/password to read |
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| Against tampering | HMAC detects any modification |
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| Against quantum adversary | `--pq` mode: ML-KEM-768 (NIST Level 3) |
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### What Zupt Does NOT Protect Against
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| Threat | Reason | Mitigation Path |
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|--------|--------|----------------|
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| Attacker who knows the password or has the private key | Fundamental to encryption | Use strong passwords (12+ chars); protect key files |
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| Cache-timing side channels (C AES) | Table-based S-box lookups | Build with Jasmin AES-NI when available |
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| Memory forensics during operation | Keys on stack during compress/extract | `zupt_secure_wipe()` on completion; `mlock()` planned |
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| Deniability | Archive header identifies format | `.zupt` magic bytes visible; ENCRYPTED flag in header |
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| Weak passwords | PBKDF2 adds ~20 bits of work factor | Use `--pq` mode for critical data |
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| Traffic analysis | Archive size reveals data volume | Outside Zupt's scope |
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| File permission/ownership | Not stored in archive | Document in COMPAT.md |
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### Quantum Threat Analysis
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**Scenario:** Adversary captures encrypted archive today, stores it, and attempts decryption when a cryptographically-relevant quantum computer is available.
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| Mode | Classical Security | Quantum Security | Verdict |
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|------|-------------------|-----------------|---------|
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| Password (`-p`) | Password-dependent + 256-bit AES | ~128-bit (Grover on AES) but PBKDF2 accelerated | **Vulnerable** — use `--pq` |
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| PQ Hybrid (`--pq`) | ~128-bit (X25519) | NIST Level 3 (ML-KEM-768) | **Protected** |
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In `--pq` mode: even if Shor's algorithm breaks X25519, ML-KEM-768 protects the archive. Even if a novel classical attack breaks ML-KEM, X25519 still provides ~128-bit security. The hybrid design ensures the archive is secure if **either** component holds.
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---
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## CSPRNG Policy
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| Platform | Primary Source | Fallback | Failure Mode |
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|----------|---------------|----------|--------------|
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| Linux | `getrandom(2)` | `/dev/urandom` | **Hard exit** — no encryption without CSPRNG |
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| macOS | `/dev/urandom` | None | **Hard exit** |
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| Windows | `RtlGenRandom` | None | **Hard exit** |
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There is no `rand()`, `srand()`, or any weak PRNG fallback anywhere in the codebase. If the OS CSPRNG is unavailable, Zupt exits with an error. This is a deliberate design choice — weak random keys are worse than no encryption.
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---
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## Supported Platforms
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| Platform | Compiler | Threading | CSPRNG | Status |
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|----------|----------|-----------|--------|--------|
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| Linux x86-64 | GCC 5+ / Clang 3.5+ | pthreads | `getrandom(2)` | **Primary** |
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| Linux ARM64 | GCC 5+ | pthreads | `getrandom(2)` | Tested |
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| macOS x86-64/ARM64 | Apple Clang | pthreads | `/dev/urandom` | Tested |
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| Windows x86-64 | MinGW / MSVC 2015+ | Win32 threads | `RtlGenRandom` | Tested |
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| FreeBSD | GCC / Clang | pthreads | `/dev/urandom` | Untested (expected to work) |
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---
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## Disclosure Timeline
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| Date | Event |
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|------|-------|
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| 2026-01-01 | v0.1.0 — Initial release |
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| 2026-03-21 | v0.5.1 — 16 security bug fixes including CSPRNG hardening |
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| 2026-03-21 | v1.0.0 — 5 critical ML-KEM bugs fixed, format frozen |
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| 2026-03-28 | v1.1.0 — X25519 formula bug fixed (not interoperable with RFC 7748) |
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| 2026-03-28 | v1.5.0 — Jasmin assembly linked (MAC verify + ML-KEM select) |
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---
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## Verification Commands
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Anyone can verify every security claim:
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```bash
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# Build
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make # Zero warnings
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# All functional tests
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make test-all # 62/62 pass
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# Memory safety
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make test-asan # Zero ASAN/UBSAN errors
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# NIST/RFC test vectors
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make test-vectors && ./test_vectors # 13/13 pass
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# Verify Jasmin symbols are active
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nm zupt | grep "zupt_mac_verify_ct\|zupt_ct_select_32"
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# Expected: T zupt_mac_verify_ct
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# T zupt_ct_select_32
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# Verify Jasmin compilation (requires jasminc)
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jasminc -arch x86-64 -o /dev/null jasmin/zupt_mac_verify.jazz
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jasminc -arch x86-64 -o /dev/null jasmin/zupt_mlkem_select.jazz
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```
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---
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© 2026 Cristian Cezar Moisés — MIT License
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