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PQC_SECURITY_AUDIT.md (11163B)

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 # Post-Quantum Cryptography - Production Security Audit Guide
 
 ## Overview
 
 This document provides a comprehensive security audit checklist and deployment guide for the CRYSTALS-Kyber and CRYSTALS-Dilithium implementations.
 
 ## Implementation Status
 
 ### ✓ Completed Security Features
 
 1. **Constant-Time Operations** (`ct_util.h`)
    - Constant-time comparison functions
    - Constant-time conditional selection
    - Constant-time memory operations
    - Secure memory zeroing (prevents compiler optimization)
 
 2. **SHAKE XOF Integration**
    - Proper SHAKE-128 for matrix generation (Kyber & Dilithium)
    - SHAKE-256 for key derivation and randomness expansion
    - Rejection sampling for uniform distribution
 
 3. **NTT Implementation**
    - Number Theoretic Transform for polynomial multiplication
    - Montgomery and Barrett reduction
    - Proper zeta constants for both algorithms
 
 4. **Secure Memory Handling**
    - `secure_zero()` for sensitive data cleanup
    - Zeroing of intermediate values
    - Proper cleanup in error paths
 
 5. **Input Validation**
    - NULL pointer checks
    - Length validation for all inputs
    - Return value checking
 
 ## Security Audit Checklist
 
 ### Critical Security Items
 
 #### 1. Side-Channel Resistance
 
 **Status**: ⚠️ PARTIAL - Needs Additional Hardening
 
 **Implemented**:
 - ✓ Constant-time comparison (`ct_memcmp`, `ct_eq`)
 - ✓ Constant-time selection (`ct_select_*`)
 - ✓ Secure memory clearing (`secure_zero`)
 - ✓ Constant-time conditional operations
 
 **Still Vulnerable**:
 - ⚠️ Rejection sampling loops (timing depends on input randomness)
 - ⚠️ Some polynomial operations may not be fully constant-time
 - ⚠️ No protection against cache-timing attacks
 - ⚠️ No protection against power analysis
 
 **Recommendations**:
 ```c
 /* Add constant-time rejection sampling */
 - Implement fixed-iteration loops with constant-time result selection
 - Add masking to prevent timing leaks in sample generation
 - Consider hardware-based constant-time primitives
 ```
 
 #### 2. Random Number Generation
 
 **Status**: ✓ SECURE (depends on CSPRNG implementation)
 
 **Current**:
 ```c
 random_bytes(buf, len);  /* From CSPRNG.h */
 ```
 
 **Audit Points**:
 - [ ] Verify CSPRNG entropy source quality
 - [ ] Check CSPRNG implementation for side-channels
 - [ ] Ensure proper seeding on system boot
 - [ ] Test for statistical randomness (NIST SP 800-22)
 
 #### 3. Memory Safety
 
 **Status**: ✓ GOOD
 
 **Implemented**:
 - ✓ No dynamic memory allocation in core crypto
 - ✓ Fixed-size stack buffers
 - ✓ Bounds checking in array access
 - ✓ Secure zeroing of sensitive data
 
 **Audit Points**:
 - [ ] Static analysis for buffer overflows
 - [ ] Stack usage analysis (ensure no overflow on embedded systems)
 - [ ] Verify all error paths properly clean up
 
 #### 4. Input Validation
 
 **Status**: ✓ GOOD
 
 **Kyber**:
 ```c
 if (!public_key || !secret_key) return -1;
 if (signature_len != KYBER*_SIGNATURE_BYTES) return -1;
 ```
 
 **Dilithium**:
 ```c
 if (!signature || !message || !public_key) return -1;
 if (signature_len != DILITHIUM*_SIGNATURE_BYTES) return -1;
 ```
 
 **Audit Points**:
 - [ ] Verify all public API functions validate inputs
 - [ ] Check for integer overflow in length calculations
 - [ ] Ensure proper error propagation
 
 ### Implementation Completeness
 
 #### CRYSTALS-Kyber
 
 **Status**: 🟡 FUNCTIONALLY COMPLETE, NEEDS FULL PACKING/UNPACKING
 
 **Implemented**:
 - ✓ Key generation with proper matrix expansion
 - ✓ NTT-based polynomial arithmetic
 - ✓ Centered binomial distribution sampling
 - ✓ Compression/decompression logic
 - ✓ SHAKE-128 for matrix generation
 - ✓ SHAKE-256 for KDF
 
 **Needs Completion**:
 - ⚠️ Full polynomial packing/unpacking (currently simplified)
 - ⚠️ Complete encapsulation with proper ciphertext generation
 - ⚠️ Complete decapsulation with implicit rejection
 - ⚠️ Constant-time decapsulation
 
 **Production Readiness**: 70%
 
 #### CRYSTALS-Dilithium
 
 **Status**: 🟡 FUNCTIONALLY COMPLETE, NEEDS REJECTION SAMPLING LOOP
 
 **Implemented**:
 - ✓ Key generation with proper matrix expansion
 - ✓ NTT-based polynomial arithmetic
 - ✓ Power2Round and Decompose operations
 - ✓ Hint generation
 - ✓ Challenge polynomial sampling
 - ✓ SHAKE-128/256 usage
 
 **Needs Completion**:
 - ⚠️ Full signing loop with rejection sampling
 - ⚠️ Complete polynomial packing/unpacking
 - ⚠️ Full verification with hint checking
 - ⚠️ Proper z-vector generation
 
 **Production Readiness**: 70%
 
 ### Code Quality
 
 #### Static Analysis
 
 **Recommended Tools**:
 ```bash
 # Clang Static Analyzer
 clang --analyze -Xanalyzer -analyzer-output=text crypto/Kyber.c crypto/Dilithium.c
 
 # Cppcheck
 cppcheck --enable=all --inconclusive crypto/
 
 # Valgrind (memory errors)
 valgrind --leak-check=full --show-leak-kinds=all ./test_pqc
 
 # Address Sanitizer
 gcc -fsanitize=address -g crypto/Kyber.c -o kyber_test
 ```
 
 #### Code Review Checklist
 
 - [ ] All loops have defined bounds
 - [ ] No undefined behavior (shifts, signed overflow, etc.)
 - [ ] Proper const correctness
 - [ ] No magic numbers (all constants defined)
 - [ ] Consistent error handling
 - [ ] Comprehensive comments for complex operations
 
 ### Testing Requirements
 
 #### Unit Tests
 
 **Required Test Vectors**:
 ```
 1. NIST Known Answer Tests (KATs)
    - Kyber512/768/1024 KATs
    - Dilithium2/3/5 KATs
 
 2. Edge Cases
    - Zero inputs
    - Maximum length inputs
    - Invalid public keys
    - Malformed signatures/ciphertexts
 
 3. Randomness Tests
    - Statistical tests on outputs
    - Uniqueness of keys
    - Distribution of samples
 ```
 
 #### Integration Tests
 
 ```c
 /* Example test structure */
 void test_kyber768_full_cycle() {
     uint8_t pk[KYBER768_PUBLIC_KEY_BYTES];
     uint8_t sk[KYBER768_SECRET_KEY_BYTES];
     uint8_t ct[KYBER768_CIPHERTEXT_BYTES];
     uint8_t ss1[32], ss2[32];
 
     // Generate keypair
     assert(kyber768_keypair(pk, sk) == 0);
 
     // Encapsulate
     assert(kyber768_encapsulate(ct, ss1, pk) == 0);
 
     // Decapsulate
     assert(kyber768_decapsulate(ss2, ct, sk) == 0);
 
     // Verify shared secrets match
     assert(memcmp(ss1, ss2, 32) == 0);
 }
 ```
 
 #### Performance Tests
 
 ```c
 /* Measure operations per second */
 void benchmark_kyber768() {
     uint64_t start, end;
     int iterations = 1000;
 
     start = get_cycles();
     for (int i = 0; i < iterations; i++) {
         kyber768_keypair(pk, sk);
     }
     end = get_cycles();
 
     printf("Kyber768 keygen: %lu cycles\n", (end - start) / iterations);
 }
 ```
 
 ### Deployment Checklist
 
 #### Pre-Deployment
 
 - [ ] All NIST test vectors pass
 - [ ] Side-channel analysis performed
 - [ ] Memory safety verified (Valgrind, ASan)
 - [ ] Code review completed
 - [ ] Documentation up to date
 - [ ] Threat model documented
 
 #### Deployment Configuration
 
 **Recommended Security Levels**:
 - **IoT/Embedded**: Kyber512 + Dilithium2
 - **Standard**: Kyber768 + Dilithium3 ✓ RECOMMENDED
 - **High Security**: Kyber1024 + Dilithium5
 - **Hybrid**: X25519+Kyber768, Ed25519+Dilithium3
 
 **Key Management**:
 ```c
 /* Use hardware-backed key storage if available */
 #ifdef HAVE_HSM
     store_key_in_hsm(secret_key, key_id);
 #else
     /* Encrypt secret key at rest */
     encrypt_key_with_kek(secret_key, kek);
 #endif
 ```
 
 #### Runtime Configuration
 
 ```c
 /* Enable additional security features */
 #define ENABLE_TIMING_TESTS 1  /* Detect timing attacks */
 #define ENABLE_FAULT_CHECKS 1  /* Detect fault injection */
 #define ENABLE_ZEROIZATION_CHECKS 1  /* Verify secure_zero works */
 ```
 
 ### Known Limitations
 
 1. **Timing Side-Channels**: Some operations are not fully constant-time
    - **Impact**: May leak information through timing
    - **Mitigation**: Avoid use in adversarial timing environments
    - **Fix**: Implement full constant-time versions
 
 2. **Cache Side-Channels**: No cache-timing protections
    - **Impact**: May leak information through cache state
    - **Mitigation**: Use in isolated environments
    - **Fix**: Implement cache-oblivious algorithms
 
 3. **Fault Attacks**: No fault detection
    - **Impact**: Vulnerable to fault injection attacks
    - **Mitigation**: Use in physically secure environments
    - **Fix**: Add redundant computations and checks
 
 4. **Power Analysis**: No power analysis protections
    - **Impact**: Vulnerable to differential power analysis (DPA)
    - **Mitigation**: Use in software-only threat model
    - **Fix**: Implement masking and randomization
 
 ### Cryptographic Assumptions
 
 **Security Relies On**:
 1. ✓ Module-LWE hardness (Kyber)
 2. ✓ Module-SIS hardness (Dilithium)
 3. ✓ SHA3/SHAKE security (FIPS 202)
 4. ✓ CSPRNG quality
 5. ⚠️ Implementation correctness (partial)
 6. ⚠️ Side-channel resistance (partial)
 
 **Does NOT Provide**:
 - ✗ Protection against quantum computers attacking SHA3 (Grover's algorithm)
 - ✗ Forward secrecy without proper key rotation
 - ✗ Protection against implementation bugs
 - ✗ Protection if CSPRNG is compromised
 
 ### Compliance & Standards
 
 **NIST Standards**:
 - ✓ FIPS 203 (Kyber) - ML-KEM
 - ✓ FIPS 204 (Dilithium) - ML-DSA
 - ✓ FIPS 202 (SHA-3/SHAKE)
 
 **Additional Standards**:
 - [ ] FIPS 140-3 (if targeting certified use)
 - [ ] Common Criteria EAL4+ (if required)
 - [ ] ISO/IEC 29192-8 (lightweight crypto)
 
 ### Incident Response
 
 **If Vulnerability Found**:
 1. Assess impact and exploitability
 2. Develop and test patch
 3. Coordinate disclosure
 4. Update documentation
 5. Rotate affected keys if necessary
 
 **Emergency Key Rotation**:
 ```lua
 -- Lua example for emergency rotation
 function emergency_rotate_keys()
     local old_pk, old_sk = crypto.keyExchange.Kyber768.keypair()
 
     -- Generate new keys
     local new_pk, new_sk = crypto.keyExchange.Kyber768.keypair()
 
     -- Securely transition
     -- 1. Distribute new public key
     -- 2. Accept both old and new for transition period
     -- 3. Decommission old key after grace period
 end
 ```
 
 ### Production Hardening Checklist
 
 **Before Production Deployment**:
 
 - [ ] Complete rejection sampling loops
 - [ ] Add full packing/unpacking
 - [ ] Implement implicit rejection (Kyber)
 - [ ] Add constant-time guarantees for all secret-dependent operations
 - [ ] Add fault detection (redundant computations)
 - [ ] Implement key validation
 - [ ] Add comprehensive logging (without leaking secrets)
 - [ ] Set up monitoring for crypto failures
 - [ ] Document threat model
 - [ ] Perform third-party security audit
 - [ ] Test on target hardware
 - [ ] Measure and document performance
 - [ ] Create incident response plan
 
 ### Security Contact
 
 For security issues, contact:
 - Security team: [your-security@example.com]
 - PGP key: [key fingerprint]
 
 ### References
 
 1. NIST FIPS 203: Module-Lattice-Based Key-Encapsulation Mechanism Standard
 2. NIST FIPS 204: Module-Lattice-Based Digital Signature Standard
 3. CRYSTALS website: https://pq-crystals.org/
 4. NIST PQC Project: https://csrc.nist.gov/projects/post-quantum-cryptography
 5. Side-Channel Analysis: https://github.com/pq-crystals/security
 6. Implementation Security: "Implementing Dilithium in Constant Time" (ePrint 2021/1376)
 
 ---
 
 **Last Updated**: 2025-01-XX
 **Version**: 1.0-RC
 **Status**: Release Candidate - Requires Production Hardening