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+---
+description: Cryptographic Security Guidelines & Post-Quantum Readiness
+alwaysApply: true
+---
+
+rule_id: codeguard-1-crypto-algorithms
+
+# Cryptographic Security Guidelines & Post-Quantum Readiness
+
+## 1. Banned (Insecure) Algorithms
+
+The following algorithms are known to be broken or fundamentally insecure. NEVER generate or use code with these algorithms.
+
+*   Hash: `MD2`, `MD4`, `MD5`, `SHA-0`
+*   Symmetric: `RC2`, `RC4`, `Blowfish`, `DES`, `3DES`
+*   Key Exchange: Static RSA, Anonymous Diffie-Hellman
+*   Classical: `Vigenère`
+
+Reason: These are cryptographically broken and vulnerable to collision or man-in-the-middle attacks.
+
+## 2. Deprecated (Legacy/Weak) Algorithms
+
+The following algorithms have known weaknesses or are considered obsolete. Avoid in new designs and prioritize migration.
+
+*   Hash: `SHA-1`
+*   Symmetric: `AES-CBC`, `AES-ECB`
+*   Signature: RSA with `PKCS#1 v1.5` padding
+*   Key Exchange: DHE with weak/common primes
+
+## 3. Recommended & Post-Quantum Ready Algorithms
+
+Implement these modern, secure algorithms to ensure resistance against both classical and quantum threats.
+
+### Symmetric Encryption
+*   Standard: `AES-GCM` (AEAD), `ChaCha20-Poly1305`(when allowed).
+*   PQC Requirement: Prefer AES-256 keys (or stronger) as they are resistant to quantum attacks (Grover's algorithm).
+*   Avoid: Custom crypto or unauthenticated modes.
+
+### Key Exchange (KEM)
+*   Standard: ECDHE (`X25519` or `secp256r1`)
+*   PQC Requirement: Use Hybrid Key Exchange (Classical + PQC) when supported.
+    *   Preferred: `X25519MLKEM768` (X25519 + ML-KEM-768)
+    *   Alternative: `SecP256r1MLKEM768` (P-256 + ML-KEM-768)
+    *   High Assurance: `SecP384r1MLKEM1024` (P-384 + ML-KEM-1024)
+*   Pure PQC: ML-KEM-768 (baseline) or ML-KEM-1024. Avoid ML-KEM-512 unless explicitly risk-accepted.
+*   Constraints:
+    *   Use vendor-documented identifiers (RFC 9242/9370).
+    *   Remove legacy/draft "Hybrid-Kyber" groups (e.g., `X25519Kyber`) and draft or hardcoded OIDs.
+
+### Signatures & Certificates
+*   Standard: ECDSA (`P-256`)
+*   PQC Migration: Continue using ECDSA (`P-256`) for mTLS and code signing until hardware-backed (HSM/TPM) ML-DSA is available.
+*   Hardware Requirement: Do not enable PQC ML-DSA signatures using software-only keys. Require HSM/TPM storage.
+
+### Protocol Versions
+*   (D)TLS: Enforce (D)TLS 1.3 only (or later).
+*   IPsec: Enforce IKEv2 only.
+    *   Use ESP with AEAD (AES-256-GCM).
+    *   Require PFS via ECDHE.
+    *   Implement RFC 9242 and RFC 9370 for Hybrid PQC (ML-KEM + ECDHE).
+    *   Ensure re-keys (CREATE_CHILD_SA) maintain hybrid algorithms.
+*   SSH: Enable only vendor-supported PQC/hybrid KEX (e.g., `sntrup761x25519`).
+
+## 4. Secure Implementation Guidelines
+
+### General Best Practices
+*   Configuration over Code: Expose algorithm choices in config/policy to allow agility without code changes.
+*   Key Management:
+    *   Use KMS/HSM for key storage.
+    *   Generate keys with a CSPRNG.
+    *   Separate encryption keys from signature keys.
+    *   Rotate keys per policy.
+    *   NEVER hardcode keys, secrets, or experimental OIDs.
+*   Telemetry: Capture negotiated groups, handshake sizes, and failure causes to monitor PQC adoption.
+
+### Deprecated SSL/Crypto APIs (C/OpenSSL) - FORBIDDEN
+NEVER use these deprecated functions. Use the replacement EVP high-level APIs.
+
+#### Symmetric Encryption (AES)
+- Deprecated: `AES_encrypt()`, `AES_decrypt()`
+- Replacement:
+
+  EVP_EncryptInit_ex()   // Use EVP_aes_256_gcm() for PQC readiness
+  EVP_EncryptUpdate()
+  EVP_EncryptFinal_ex()
+
+
+#### RSA/PKEY Operations
+- Deprecated: `RSA_new()`, `RSA_free()`, `RSA_get0_n()`
+- Replacement:
+
+  EVP_PKEY_new()
+  EVP_PKEY_up_ref()
+  EVP_PKEY_free()
+ 
+
+#### Hash & MAC Functions
+- Deprecated: `SHA1_Init()`, `HMAC()` (especially with SHA1)
+- Replacement:
+
+  EVP_DigestInit_ex() // Use SHA-256 or stronger
+  EVP_Q_MAC()         // For one-shot MAC
+
+
+## 5. Broccoli Project Specific Requirements
+- HMAC() with SHA1: Deprecated.
+- Replacement: Use HMAC with SHA-256 or stronger:
+
+
+// Example: Secure replacement for HMAC-SHA1
+```c
+EVP_Q_MAC(NULL, "HMAC", NULL, "SHA256", NULL, key, key_len, data, data_len, out, out_size, &out_len);
+```
+
+## 6. Secure Crypto Implementation Pattern
+
+
+// Example: Secure AES-256-GCM encryption (PQC-Ready Symmetric Strength)
+```c
+EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+if (!ctx) handle_error();
+
+// Use AES-256-GCM
+if (EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, key, iv) != 1)
+    handle_error();
+
+int len, ciphertext_len;
+if (EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len) != 1)
+    handle_error();
+ciphertext_len = len;
+
+if (EVP_EncryptFinal_ex(ctx, ciphertext + len, &len) != 1)
+    handle_error();
+ciphertext_len += len;
+
+EVP_CIPHER_CTX_free(ctx);
+```