sodium_crypto_box_seal

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_box_seal — Anonymous public-key encryption

Description

sodium_crypto_box_seal(#[\SensitiveParameter] string $message, string $public_key): string

Encrypt a message such that only the recipient can decrypt it.

Unlike with sodium_crypto_box(), you only need to know the recipient's public key to use sodium_crypto_box_seal(). One consequence of this convenience, however, is that the ciphertext isn't bound to a static public key, and is therefore not authenticated. Hence, anonymous public-key encryption.

sodium_crypto_box_seal() still provides ciphertext integrity. Just not sender identity authentication.

If you also need sender authentication, the sodium_crypto_sign() functions are likely the best place to start.

Parameters

message: The message to encrypt.
public_key: The public key that corresponds to the only key that can decrypt the message.

Return Values

A ciphertext string in the format of (one-time public key, encrypted message, authentication tag).

Examples

Example #1 sodium_crypto_box_seal() example

<?php
$keypair = sodium_crypto_box_keypair();
$public_key = sodium_crypto_box_publickey($keypair);

// Obfuscated plaintext to make the example more fun
$plaintext_b64 = "V3JpdGluZyBzb2Z0d2FyZSBpbiBQSFAgY2FuIGJlIGEgZGVsaWdodCE=";
$decoded_plaintext = sodium_base642bin($plaintext_b64, SODIUM_BASE64_VARIANT_ORIGINAL);

$sealed = sodium_crypto_box_seal($decoded_plaintext, $public_key);
var_dump(base64_encode($sealed));

$opened = sodium_crypto_box_seal_open($sealed, $keypair);
var_dump($opened);
?>

The above example will output something similar to:

string(120) "oRBXXAV4iQBrxlV4A21Bord8Yo/D8ZlrIIGNyaRCcGBfpz0map52I3xq6l+CST+1NSgQkbV+HiYyFjXWiWiaCGupGf+zl4bgWj/A9Adtem7Jt3h3emrMsLw="
string(41) "Writing software in PHP can be a delight!"

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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_seal(); where you have 2 people exchanging a $message - person 1 encrypts it so that only person 2 can decrypt it. It does not allow person 2 to know who sent it, as only their public key way used (see sodium_crypto_box to do that).

<?php

$keypair = sodium_crypto_box_keypair();
$keypair_public = sodium_crypto_box_publickey($keypair);
$keypair_secret = sodium_crypto_box_secretkey($keypair);

// $key_public = sodium_crypto_box_publickey_from_secretkey($keypair_secret);
// $keypair = sodium_crypto_box_keypair_from_secretkey_and_publickey($keypair_secret, $key_public);

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

$message = 'hello';

$encrypted = sodium_crypto_box_seal($message, $keypair_public);

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

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

$decrypted = sodium_crypto_box_seal_open($encrypted, $keypair);

echo $decrypted . "\n";

?>

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