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skills/software-security/rules/codeguard-1-crypto-algorithms.md

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+---
+description: Cryptographic Security Guidelines
+alwaysApply: true
+---
+
+rule_id: codeguard-1-crypto-algorithms
+
+# Cryptographic Security Guidelines
+
+## Banned (Insecure) Algorithms
+
+The following algorithms are known to be broken or fundamentally insecure. **NEVER** generate or use code with these algorithms.
+Examples:
+
+* Hash: `MD2`, `MD4`, `MD5`, `SHA-0`
+* Symmetric: `RC2`, `RC4`, `Blowfish`, `DES`, `3DES`
+* Key Exchange: Static RSA, Anonymous Diffie-Hellman
+* Classical: `Vigenère`
+
+## Deprecated (Legacy/Weak) Algorithms
+
+The following algorithms are not outright broken, but have known weaknesses, or are considered obsolete. **NEVER** generate or use code with these algorithms.
+Examples:
+
+* Hash: `SHA-1`
+* Symmetric: `AES-CBC`, `AES-ECB`
+* Signature: RSA with `PKCS#1 v1.5` padding
+* Key Exchange: DHE with weak/common primes
+
+
+## Deprecated SSL/Crypto APIs - FORBIDDEN
+NEVER use these deprecated functions. Use the replacement APIs listed below:
+
+### Symmetric Encryption (AES)
+- Deprecated: `AES_encrypt()`, `AES_decrypt()`
+- Replacement: Use EVP high-level APIs:
+  ```c
+  EVP_EncryptInit_ex()
+  EVP_EncryptUpdate()
+  EVP_EncryptFinal_ex()
+  EVP_DecryptInit_ex()
+  EVP_DecryptUpdate()
+  EVP_DecryptFinal_ex()
+  ```
+
+### RSA Operations
+- Deprecated: `RSA_new()`, `RSA_up_ref()`, `RSA_free()`, `RSA_set0_crt_params()`, `RSA_get0_n()`
+- Replacement: Use EVP key management APIs:
+  ```c
+  EVP_PKEY_new()
+  EVP_PKEY_up_ref()
+  EVP_PKEY_free()
+  ```
+
+### Hash Functions
+- Deprecated: `SHA1_Init()`, `SHA1_Update()`, `SHA1_Final()`
+- Replacement: Use EVP digest APIs:
+  ```c
+  EVP_DigestInit_ex()
+  EVP_DigestUpdate()
+  EVP_DigestFinal_ex()
+  EVP_Q_digest()  // For simple one-shot hashing
+  ```
+
+### MAC Operations
+- Deprecated: `CMAC_Init()`, `HMAC()` (especially with SHA1)
+- Replacement: Use EVP MAC APIs:
+  ```c
+  EVP_Q_MAC()  // For simple MAC operations
+  ```
+
+### Key Wrapping
+- Deprecated: `AES_wrap_key()`, `AES_unwrap_key()`
+- Replacement: Use EVP key wrapping APIs or implement using EVP encryption
+
+### Other Deprecated Functions
+- Deprecated: `DSA_sign()`, `DH_check()`
+- Replacement: Use corresponding EVP APIs for DSA and DH operations
+
+## Banned Insecure Algorithms - STRICTLY FORBIDDEN
+These algorithms MUST NOT be used in any form:
+
+### Hash Algorithms (Banned)
+- MD2, MD4, MD5, SHA-0
+- Reason: Cryptographically broken, vulnerable to collision attacks
+- Use Instead: SHA-256, SHA-384, SHA-512
+
+### Symmetric Ciphers (Banned)
+- RC2, RC4, Blowfish, DES, 3DES
+- Reason: Weak key sizes, known vulnerabilities
+- Use Instead: AES-128, AES-256, ChaCha20
+
+### Key Exchange (Banned)
+- Static RSA key exchange
+- Anonymous Diffie-Hellman
+- Reason: No forward secrecy, vulnerable to man-in-the-middle attacks
+- Use Instead: ECDHE, DHE with proper validation
+
+## Broccoli Project Specific Requirements
+- HMAC() with SHA1: Deprecated per Broccoli project requirements
+- Replacement: Use HMAC with SHA-256 or stronger:
+  ```c
+  // Instead of HMAC() with SHA1
+  EVP_Q_MAC(NULL, "HMAC", NULL, "SHA256", NULL, key, key_len, data, data_len, out, out_size, &out_len);
+  ```
+
+## Secure Crypto Implementation Pattern
+```c
+// Example: Secure AES encryption
+EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+if (!ctx) handle_error();
+
+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);
+```
+
+## Code Review Checklist
+- [ ] No deprecated SSL/crypto APIs used
+- [ ] No banned algorithms (MD5, DES, RC4, etc.)
+- [ ] HMAC uses SHA-256 or stronger (not SHA1)
+- [ ] All crypto operations use EVP high-level APIs
+- [ ] Proper error handling for all crypto operations
+- [ ] Key material properly zeroed after use