README

ChaCha20 in PHP

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This library contains a pure PHP implementation of the ChaCha20 encryption algorithm.

The library has been written to be high performance (relative to PHP), not pretty. It obviously doesn't perform anywhere close to a native implementation.

Usage:

Remember that a nonce must not be used more than once for a particular key

$chacha20 = new ChaCha20\Cipher;
$encCtx = $chacha20->init($key, $nonce);
$decCtx = $chacha20->init($key, $nonce);

$cipherText = $chacha20->encrypt($encCtx, $message);
$plainText = $chacha20->decrypt($decCtx, $cipherText);

The Context object maintains the current state of the algorithm, so that it can be used in a streaming scenario. Therefore an application performing simultaneous encryption and decryption will need to main two contexts.

The decrypt method is an alias of the encrypt method, and exists only to indicate intent.

Seek operations can be performed on the keystream by calling the setCounter method, where the count is in 64-byte blocks.