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README.md

Sodium Compat

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Sodium Compat is a pure PHP polyfill for the Sodium cryptography library (libsodium), otherwise available in PECL.

This library tentativeley supports PHP 5.2.4 - 7.x (latest), but officially only supports non-EOL'd versions of PHP.

If you have the PHP extension installed, Sodium Compat will opportunistically and transparently use the PHP extension instead of our implementation.

IMPORTANT!

Danger: Experimental

This is an experimental cryptography library. It has not been formally audited by an independent third party that specializes in cryptography or cryptanalysis.

Until it has received a clean bill of health from independent computer security experts, use this library at your own risk.

The code is currently frozen, pending the results of the cryptography audit.

Installing Sodium Compat

If you're using Composer:

composer require paragonie/sodium_compat

If you're not using Composer, download a release tarball (which should be signed with our GnuPG public key), extract its contents, then include our autoload.php script in your project.

<?php
require_once "/path/to/sodium_compat/autoload.php";

Using Sodium Compat

True Polyfill

If you're using PHP 5.3.0 or newer and do not have the PECL extension installed, you can just use the standard ext/sodium API features as-is and the polyfill will work its magic.

<?php
require_once "/path/to/sodium_compat/autoload.php";

$alice_kp = \Sodium\crypto_sign_keypair();
$alice_sk = \Sodium\crypto_sign_secretkey($alice_kp);
$alice_pk = \Sodium\crypto_sign_publickey($alice_kp);

$message = 'This is a test message.';
$signature = \Sodium\crypto_sign_detached($message, $alice_sk);
if (\Sodium\crypto_sign_verify_detached($signature, $message, $alice_pk)) {
    echo 'OK', PHP_EOL;
} else {
    throw new Exception('Invalid signature');
}

The polyfill does not expose this API on PHP < 5.3, or if you have the PHP extension installed already.

PHP 7.2 Polyfill

As per the second vote on the libsodium RFC, PHP 7.2 uses sodium_* instead of \Sodium\*.

<?php
require_once "/path/to/sodium_compat/autoload.php";

$alice_kp = sodium_crypto_sign_keypair();
$alice_sk = sodium_crypto_sign_secretkey($alice_kp);
$alice_pk = sodium_crypto_sign_publickey($alice_kp);

$message = 'This is a test message.';
$signature = sodium_crypto_sign_detached($message, $alice_sk);
if (sodium_crypto_sign_verify_detached($signature, $message, $alice_pk)) {
    echo 'OK', PHP_EOL;
} else {
    throw new Exception('Invalid signature');
}

Since this doesn't require a namespace, this API is exposed on PHP 5.2.

General-Use Polyfill

If your users are on PHP < 5.3, or you want to write code that will work whether or not the PECL extension is available, you'll want to use the ParagonIE_Sodium_Compat class for most of your libsodium needs.

The above example, written for general use:

<?php
require_once "/path/to/sodium_compat/autoload.php";

$alice_kp = ParagonIE_Sodium_Compat::crypto_sign_keypair();
$alice_sk = ParagonIE_Sodium_Compat::crypto_sign_secretkey($alice_kp);
$alice_pk = ParagonIE_Sodium_Compat::crypto_sign_publickey($alice_kp);

$message = 'This is a test message.';
$signature = ParagonIE_Sodium_Compat::crypto_sign_detached($message, $alice_sk);
if (ParagonIE_Sodium_Compat::crypto_sign_verify_detached($signature, $message, $alice_pk)) {
    echo 'OK', PHP_EOL;
} else {
    throw new Exception('Invalid signature');
}

Generally: If you replace \Sodium\ with ParagonIE_Sodium_Compat::, any code already written for the libsodium PHP extension should work with our polyfill without additional code changes.

To learn how to use Libsodium, read Using Libsodium in PHP Projects.

Help, Sodium_Compat is Slow! How can I make it fast?

There are three ways to make it fast:

  1. Use PHP 7.2 when it comes out, and take advantage of libsodium in the core.
  2. Install the libsodium PHP extension from PECL.
  3. Only if the previous two options are not available for you:
    1. Verify that the processor you're using actually implements constant-time multiplication. Sodium_compat does, but it trades some speed for cross-platform security.
    2. Only if you are 100% certain that your processor is safe, you can set ParagonIE_Sodium_Compat::$fastMul = true; without harming the security of your cryptography keys. If your processor isn't safe, then decide whether you want speed or security because you can't have both.

API Coverage

  • Mainline NaCl Features
    • crypto_auth()
    • crypto_auth_verify()
    • crypto_box()
    • crypto_box_open()
    • crypto_scalarmult()
    • crypto_secretbox()
    • crypto_secretbox_open()
    • crypto_sign()
    • crypto_sign_open()
  • PECL Libsodium Features
    • crypto_aead_chacha20poly1305_encrypt()
    • crypto_aead_chacha20poly1305_decrypt()
    • crypto_aead_chacha20poly1305_ietf_encrypt()
    • crypto_aead_chacha20poly1305_ietf_decrypt()
    • crypto_box_seal()
    • crypto_box_seal_open()
    • crypto_generichash()
    • crypto_generichash_init()
    • crypto_generichash_update()
    • crypto_generichash_final()
    • crypto_kx()
    • crypto_shorthash()
    • crypto_sign_detached()
    • crypto_sign_verify_detached()
    • For advanced users only:
      • crypto_stream()
      • crypto_stream_xor()
    • Other utilities (e.g. crypto_*_keypair())

Cryptography Primitives Provided

  • X25519 - Elliptic Curve Diffie Hellman over Curve25519
  • Ed25519 - Edwards curve Digital Signature Algorithm over Curve25519
  • Xsalsa20 - Extended-nonce Salsa20 stream cipher
  • ChaCha20 - Stream cipher
  • Poly1305 - Polynomial Evaluation Message Authentication Code modulo 2^130 - 5
  • BLAKE2b - Cryptographic Hash Function
  • SipHash-2-4 - Fast hash, but not collision-resistant; ideal for hash tables.

Features Excluded from this Polyfill

  • \Sodium\memzero() - Although we expose this API endpoint, we can't reliably zero buffers from PHP.

    If you have the PHP extension installed, sodium_compat will use the native implementation to zero out the string provided. Otherwise it will throw an Error (provided as part of the random_compat polyfill).

  • \Sodium\crypto_pwhash() - It's not feasible to polyfill scrypt or Argon2 into PHP and get reasonable performance. Users would feel motivated to select parameters that downgrade security to avoid denial of service (DoS) attacks.

    The only winning move is not to play.