A04:2025 — Cryptographic Failures

01 Core Cryptographic Flaw Mechanisms

Cryptographic failures occur when systems fail to adequately protect data at rest and in transit. The common architectural failure modes include:

Weak or Broken Algorithms: Utilizing obsolete hashing algorithms like MD5/SHA1 for security credentials, or symmetric ciphers like DES/3DES/RC4.
Insecure Password Storage: Using single-iteration cryptographic hash functions (e.g. standard SHA-256) instead of memory-hard, work-factored algorithms (Argon2id, bcrypt, PBKDF2).
Insecure PRNG (Pseudo-Random Number Generator): Using non-cryptographic RNGs like rand() or Math.random() for tokens, password reset nonces, and session identifiers.
Hardcoded and Committed Secrets: Embedding encryption keys, API signing secrets, or private keys directly in source code repositories.
Unauthenticated Encryption Modes: Utilizing AES-CBC without HMAC verification, leaving systems vulnerable to padding oracle attacks.

02 Vulnerability Demonstration & Test Triggers

Vulnerable Implementation: Insecure Token Generation & Weak Password Hash

Below is a typical vulnerable PHP backend using predictable PRNG and un-salted, fast hashing.

vulnerable_auth.phpPHP

// VULNERABILITY 1: Fast un-salted hash (susceptible to precomputed rainbow tables)
function storePassword($user, $plainPassword) {
    $hashed = md5($plainPassword); // Broken & fast algorithm
    saveToDb($user, $hashed);
}

// VULNERABILITY 2: Predictable pseudo-random generator for reset tokens
function generatePasswordResetToken($user) {
    // rand() is seeded by time/process state - easily predictable
    $token = md5(rand() . time() . $user);
    saveResetToken($user, $token);
    return $token;
}

Reproduction & Verification Procedure

1

Analyze Token Predictability:

Generate 50 sequential reset tokens and calculate state predictability using PRNG seed reconstruction.

2

Check Transport Encryption:

Inspect network transit headers to verify lack of HSTS and cleartext transmission over HTTP.

curl -I -k http://example.com/api/v1/auth/login
# Look for missing Strict-Transport-Security header

03 Audit & Static Code Analysis Rules

Search patterns for detecting cryptographic anti-patterns across codebases:

Anti-Pattern	Grep / AST Signature	Severity
Weak Hash for Auth	`md5\(\|sha1\(\|hash\(['"]sha1`	Critical
Insecure PRNG	`rand\(\|mt_rand\(\|Math\.random\(\)`	High
Hardcoded Secrets	`(api_key\|secret_key\|jwt_secret)\s=\s['"][a-zA-Z0-9_\-]{8,}`	Critical
Insecure Cipher Mode	`AES-.*-ECB\|DES\|RC4`	Critical

04 Hardened Remediation Standards

Hardened Cryptographic Implementation

secure_crypto.phpPHP 8+

// 1. Password Hashing using Argon2id or bcrypt with adaptive cost
function secureStorePassword($user, $plainPassword) {
    $hashed = password_hash($plainPassword, PASSWORD_ARGON2ID, [
        'memory_cost' => 65536,
        'time_cost'   => 4,
        'threads'     => 1
    ]);
    saveToDb($user, $hashed);
}

// 2. Cryptographically Secure PRNG Token Generation
function secureGenerateResetToken($user) {
    // 256 bits of CSPRNG entropy
    $randomBytes = random_bytes(32);
    $token = bin2hex($randomBytes);
    
    // Store token hash in database, not raw token
    $tokenHash = hash('sha256', $token);
    saveResetTokenHash($user, $tokenHash, time() + 900); // 15 min TTL
    return $token;
}

// 3. Authenticated Symmetric Encryption (AES-256-GCM)
function secureEncryptPayload(string $plaintext, string $key): array {
    $iv = random_bytes(12); // Standard 96-bit IV for GCM
    $tag = "";
    $ciphertext = openssl_encrypt(
        $plaintext,
        'aes-256-gcm',
        $key,
        OPENSSL_RAW_DATA,
        $iv,
        $tag,
        "",
        16 // 128-bit authentication tag
    );
    return [
        'ciphertext' => base64_encode($ciphertext),
        'iv'         => base64_encode($iv),
        'tag'        => base64_encode($tag)
    ];
}

05 Verification & Compliance Checklist

Check Item	Requirement	Status
TLS Configuration	TLS 1.2 minimum required, TLS 1.3 preferred with modern cipher suites.	Mandatory
Password Storage	Passlib/Argon2id or bcrypt with cost factor ≥ 12.	Mandatory
Key Management	No hardcoded secrets; use AWS KMS, HashiCorp Vault, or environment secrets.	Mandatory
Data at Rest	Sensitive PII encrypted using AES-256-GCM authenticated cipher.	Mandatory