Friendica Communications Platform (please note that this is a clone of the repository at github, issues are handled there)
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This is a class for doing symmetric encryption in PHP. Requires PHP 5.4 or newer.

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Messages are encrypted with AES-128 in CBC mode and are authenticated with HMAC-SHA256 (Encrypt-then-Mac). PKCS7 padding is used to pad the message to a multiple of the block size. HKDF is used to split the user-provided key into two keys: one for encryption, and the other for authentication. It is implemented using the openssl_ and hash_hmac functions.


This is new code, and it hasn't received much review by experts. I have spent many hours making it as secure as possible (extensive runtime tests, secure coding practices), and auditing it for problems, but I may have missed some issues. So be careful. Don't trust it with your life. Check out the open GitHub issues for a list of known issues. If you find a problem with this library, please report it by opening a GitHub issue.

That said, you're probably much better off using this library than any other encryption library written in PHP.


This library was created after noticing how much insecure PHP encryption code there is. I once did a Google search for "php encryption" and found insecure code or advice on 9 of the top 10 results.

Encryption is becoming an essential component of modern websites. This library aims to fulfil a subset of that need: Authenticated symmetric encryption of short strings, given a random key.

This library is developed around several core values:

  • Rule #1: Security is prioritized over everything else.

    Whenever there is a conflict between security and some other property, security will be favored. For example, the library has runtime tests, which make it slower, but will hopefully stop it from encrypting stuff if the platform it's running on is broken.

  • Rule #2: It should be difficult to misuse the library.

    We assume the developers using this library have no experience with cryptography. We only assume that they know that the "key" is something you need to encrypt and decrypt the messages, and that it must be protected. Whenever possible, the library should refuse to encrypt or decrypt messages when it is not being used correctly.

  • Rule #3: The library aims only to be compatible with itself.

    Other PHP encryption libraries try to support every possible type of encryption, even the insecure ones (e.g. ECB mode). Because there are so many options, inexperienced developers must make decisions between things like "CBC" mode and "ECB" mode, knowing nothing about either one, which inevitably creates vulnerabilities.

    This library will only support one secure mode. A developer using this library will call "encrypt" and "decrypt" not caring about how they are implemented.

  • Rule #4: The library should consist of a single PHP file and nothing more.

    Some PHP encryption libraries, like libsodium-php [1], are not straightforward to install and cannot packaged with "just download and extract" applications. This library will always be just one PHP file that you can put in your source tree and require().