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

description, alwaysApply

description	alwaysApply
Cryptographic Security Guidelines	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:

  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:

  EVP_PKEY_new()
  EVP_PKEY_up_ref()
  EVP_PKEY_free()
  

Hash Functions

• Deprecated: SHA1_Init(), SHA1_Update(), SHA1_Final()
• Replacement: Use EVP digest APIs:

  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:

  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:

  // 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

// 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