OpenSslKeyLengthMismatch

warning native on by default

Group: Security

OpenSSL keys must match the chosen cipher's required byte length. Supply a correctly sized key instead of relying on padding or truncation.

Example

<?php
openssl_encrypt($data,"aes-256-gcm",random_bytes(16),OPENSSL_RAW_DATA,$iv,$tag);

Reported:

• line 2: Provide the cipher-required key length.

Detection

• Resolved openssl_encrypt/decrypt uses a literal aes-128/192/256 cipher variant; key byte length is proven and differs from 16/24/32 respectively. Track literal string, str_repeat, random_bytes and unmodified local values. Unknown cipher/key produces no report.
• D2. Resolve builtin functions, classes, constants and methods; user-defined lookalikes are excluded. Follow only bounded local proof in one lexical scope.
• Emit one finding per violating operation, not per supporting evidence statement. When the proof is inconclusive, nothing is reported.

Exceptions (no report)

• Do not report unresolved or shadowed builtin names, unknown values, or incomplete receiver/type provenance. Unknown calls, aliases escaping, and intervening writes invalidate local proof. Similar code outside the stated detection contract is not a finding.

• A variable key is not reported when its proven value can be replaced by code that local flow does not follow:

  • a closure in the same scope captures the variable by reference, or an array item stores a reference to it;
  • the scope calls builtin extract(), which can define any local variable (include/require and eval already make local flow incomplete, D2);
  • the variable shares storage with other code — a file-level variable, one bound with global, a by-reference parameter, or a by-reference capture of the enclosing closure — and a call that may run user code (a method or static call, an object creation, or a function call other than a builtin whose signature has no callable parameter) or a $GLOBALS access follows the proving assignment (arguments of the checked call included), or the global binding itself follows that assignment. Builtins such as random_bytes() or base64_encode() do not weaken the proof.

  By-value captures, arrow functions and bindings of other variables do not weaken the proof.

• Both standard suppression forms suppress this native ID.

Fix

None. Choosing a repair requires intent or additional runtime information.

PHP versions

Available throughout supported PHP 5.3–8.5 where the referenced builtin/extension is available. Respect syntax/version-specific receiver contracts; unavailable APIs are not this rule’s concern.

Configure

In custos.json:

{
  "rules": {
    "OpenSslKeyLengthMismatch": {
      "enabled": false
    }
  }
}

Suppress

Before the statement or declaration (or the first statement of the file):

// @custos-ignore OpenSslKeyLengthMismatch