quantum-crypto-agility

# Intent-Based Cryptographic API Design for PQC Migration Methodology from arXiv:2606.13445 for designing cryptographic APIs that support cryptographic agility during post-quantum cryptography (PQC) migration. ## Problem Most cryptographic APIs are designed around specific algorithms (RSA, ECC, AES). Migrating to PQC (ML-KEM, ML-DSA, SLH-DSA) requires: - Rewiring explicit algorithm references across large codebases - Testing each integration point - Managing hybrid (classical + PQC) transition periods ## Intent-Based API Pattern ### Core Design Principle Instead of: `crypto.encrypt("RSA-OAEP", plaintext, key)` Use: `crypto.encrypt({intent: "confidentiality", security_level: 5}, plaintext)` ### API Structure ``` CryptoService ├── encrypt(intent: CryptoIntent, data: bytes) → bytes ├── decrypt(intent: CryptoIntent, ciphertext: bytes) → bytes ├── sign(intent: CryptoIntent, data: bytes) → bytes ├── verify(intent: CryptoIntent, data: bytes, signature: bytes) → bool └── derive(intent: CryptoIntent, input: bytes) → bytes CryptoIntent { purpose: "confidentiality" | "integrity" | "authentication" | "non-repudiation" security_level: 1 | 2 | 3 | 4 | 5 // NIST PQC levels performance_tier: "low_latency" | "balanced" | "high_throughput" compliance: ["fips140-3", "pqc-ready"] } ``` ### Implementation Steps 1. **Define Intent Taxonomy**: Map security requirements to intent objects 2. **Build Algorithm Registry**: Map intents to concrete algorithms with fallbacks 3. **Implement Policy Engine**: Select algorithms based on intent + policy 4. **Add Migration Layer**: Gradually swap classical → PQC in registry 5. **Audit Trail**: Log which algorithm was used for each operation ### Algorithm Registry Pattern ```yaml registry: confidentiality: level_1: [ML-KEM-512, X25519] # hybrid level_3: [ML-KEM-768, X448] # hybrid level_5: [ML-KEM-1024] # pure PQC integrity: level_1: [ML-DSA-44, Ed25519] level_3: [ML-DSA-65, Ed448] level_5: [ML-DSA-87] ``` ### Migration Strategy 1. **Phase 1**: Intent layer + classical algorithms (no code changes in consumers) 2. **Phase 2**: Add PQC algorithms to registry as options 3. **Phase 3**: Enable hybrid mode (classical + PQC) 4. **Phase 4**: Switch default to PQC-only 5. **Phase 5**: Remove classical algorithms from registry ## Pitfalls - **Intent ambiguity**: Vague intents lead to wrong algorithm selection - **Performance regression**: PQC can be slower; need performance_tier - **Key size growth**: PQC keys are larger; consider storage/network limits - **Compliance gaps**: Not all PQC algorithms are FIPS-approved yet - **Side channels**: PQC implementations may have different side-channel profiles ## References - arXiv:2606.13445 - "Intent-Based Cryptographic API Design for Cryptographic Agility" - NIST PQC Standardization: ML-KEM (FIPS 203), ML-DSA (FIPS 204), SLH-DSA (FIPS 205)