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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