php runtime_error ai_generated true

Warning: openssl_encrypt(): IV passed is 16 bytes long which is longer than the 8 bytes expected by selected cipher, truncating in /var/www/app/src/Crypto/Encryptor.php on line 23

ID: php/openssl-iv-length-mismatch

Also available as: JSON · Markdown · 中文
90%Fix Rate
87%Confidence
1Evidence
2024-01-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
php 8.1 active — — —
php 8.2 active — — —
php 8.3 active — — —
OpenSSL 3.0 active — — —

Root Cause

The initialization vector (IV) length provided to `openssl_encrypt` or `openssl_decrypt` does not match the block size required by the selected cipher method (e.g., AES-128-CBC expects 16 bytes, but DES expects 8 bytes).

generic

中文

提供给 `openssl_encrypt` 或 `openssl_decrypt` 的初始化向量（IV）长度与所选密码方法所需的块大小不匹配（例如，AES-128-CBC 需要 16 字节，而 DES 需要 8 字节）。

Official Documentation

https://www.php.net/manual/en/function.openssl-encrypt.php

Workarounds

  1. 95% success Use `openssl_cipher_iv_length($cipher)` to determine the correct IV length, then generate the IV accordingly: `$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));` 
    Use `openssl_cipher_iv_length($cipher)` to determine the correct IV length, then generate the IV accordingly: `$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));`
  2. 90% success Explicitly set the cipher method to match the IV length, e.g., change from `'des'` to `'aes-128-cbc'` if the IV is 16 bytes. 
    Explicitly set the cipher method to match the IV length, e.g., change from `'des'` to `'aes-128-cbc'` if the IV is 16 bytes.

中文步骤

  1. Use `openssl_cipher_iv_length($cipher)` to determine the correct IV length, then generate the IV accordingly: `$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));`
  2. Explicitly set the cipher method to match the IV length, e.g., change from `'des'` to `'aes-128-cbc'` if the IV is 16 bytes.

Dead Ends

Common approaches that don't work:

  1. Ignoring the warning and continuing execution 95% fail

    Truncation of the IV can cause decryption failures or security vulnerabilities; the data may not be recoverable or may be improperly encrypted.

  2. Using `openssl_random_pseudo_bytes` without specifying the correct length 70% fail

    The function defaults to 16 bytes, which may be incorrect for ciphers like DES (8 bytes) or RC4 (no IV); the length must match the cipher's block size.