sodium_crypto_box

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_box — Authenticated public-key encryption

Description

sodium_crypto_box(#[\SensitiveParameter] string $message, string $nonce, #[\SensitiveParameter] string $key_pair): string

Encrypt a message using asymmetric (public key) cryptography.

The algorithm used by functions prefixed with sodium_crypto_box() are Elliptic Curve Diffie-Hellman over the Montgomery curve, Curve25519; usually abbreviated as X25519.

Parameters

message: The message to be encrypted.
nonce: A number that must be only used once, per message. 24 bytes long. This is a large enough bound to generate randomly (i.e. random_bytes()).
key_pair: See sodium_crypto_box_keypair_from_secretkey_and_publickey(). This should include the sender's X25519 secret key and the recipient's X25519 public key.

Return Values

Returns the encrypted message (ciphertext plus authentication tag). The ciphertext will be 16 bytes longer than the plaintext, and a raw binary string. See sodium_bin2base64() for safe encoding for storage.

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User Contributed Notes 1 note

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craig at craigfrancis dot co dot uk ¶

6 years ago

Here's a quick example on how to use sodium_crypto_box(); where you have 2 people exchanging a $message, where person 1 encrypts it so that only person 2 can decrypt it, and be sure that person 1 actually sent it (without it being tampered with).

<?php

$keypair1 = sodium_crypto_box_keypair();
$keypair1_public = sodium_crypto_box_publickey($keypair1);
$keypair1_secret = sodium_crypto_box_secretkey($keypair1);

$keypair2 = sodium_crypto_box_keypair();
$keypair2_public = sodium_crypto_box_publickey($keypair2);
$keypair2_secret = sodium_crypto_box_secretkey($keypair2);

//--------------------------------------------------
// Person 1, encrypting

$message = 'hello';

$nonce = random_bytes(SODIUM_CRYPTO_BOX_NONCEBYTES);

$encryption_key = sodium_crypto_box_keypair_from_secretkey_and_publickey($keypair1_secret, $keypair2_public);
$encrypted = sodium_crypto_box($message, $nonce, $encryption_key);

echo base64_encode($encrypted) . "\n";

//--------------------------------------------------
// Person 2, decrypting

$decryption_key = sodium_crypto_box_keypair_from_secretkey_and_publickey($keypair2_secret, $keypair1_public);
$decrypted = sodium_crypto_box_open($encrypted, $nonce, $decryption_key);

echo $decrypted . "\n";

?>

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