Cryptography, Hashing and Passwords

<?php

declare(strict_types=1);

echo hash('sha256', 'Kindred'), "\n";
echo hash('xxh3', 'Kindred'), "\n";               // fast, non-cryptographic

// Signed download link for a member's loan history
$key = random_bytes(32);                          // in real code: a secret loaded from the environment
$query = http_build_query(['member' => 'M-17', 'expires' => 1_791_300_000]);
$signature = hash_hmac('sha256', $query, $key);
$url = "/loans/export?{$query}&signature={$signature}";

// Verifying a request
parse_str(parse_url($url, PHP_URL_QUERY), $params);
$given = $params['signature'];
unset($params['signature']);
$expected = hash_hmac('sha256', http_build_query($params), $key);
var_dump(hash_equals($expected, $given));          // bool(true) -- constant-time comparison
var_dump((int) $params['expires'] > 1_791_200_000); // and check the expiry

<?php

declare(strict_types=1);

// Registration
$hash = password_hash('correct horse battery staple', PASSWORD_DEFAULT);
echo substr($hash, 0, 7), ' (', strlen($hash), " chars)\n";            // $2y$12$ (60 chars)

// Login
function login(string $password, string $storedHash): bool
{
    if (!password_verify($password, $storedHash)) {
        return false;
    }
    if (password_needs_rehash($storedHash, PASSWORD_DEFAULT)) {        // e.g. after raising the cost
        $newHash = password_hash($password, PASSWORD_DEFAULT);
        // save $newHash for this user
    }
    return true;
}

var_dump(login('correct horse battery staple', $hash), login('Tr0ub4dor&3', $hash));   // bool(true) bool(false)

$argon = password_hash('correct horse battery staple', PASSWORD_ARGON2ID);
print_r(password_get_info($argon)['options']);    // memory_cost 65536, time_cost 4, threads 1

<?php

declare(strict_types=1);

// Symmetric: encrypting a member's private note at rest
$key = sodium_crypto_secretbox_keygen();                         // 32 random bytes; store it outside the database
$nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES);       // unique per message, stored with the ciphertext
$ciphertext = sodium_crypto_secretbox('prefers large print', $nonce, $key);
$stored = base64_encode($nonce . $ciphertext);

$decoded = base64_decode($stored);
$plain = sodium_crypto_secretbox_open(
    substr($decoded, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES),
    substr($decoded, 0, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES),
    $key,
);
var_dump($plain);                                                // string(19) "prefers large print"
var_dump(sodium_crypto_secretbox_open($ciphertext, $nonce, sodium_crypto_secretbox_keygen()));   // bool(false): wrong key

// AEAD: bind the ciphertext to the record it belongs to
$aeadKey = sodium_crypto_aead_xchacha20poly1305_ietf_keygen();
$aeadNonce = random_bytes(SODIUM_CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES);
$sealed = sodium_crypto_aead_xchacha20poly1305_ietf_encrypt('phone: 555-0100', 'member:M-17', $aeadNonce, $aeadKey);
var_dump(sodium_crypto_aead_xchacha20poly1305_ietf_decrypt($sealed, 'member:M-42', $aeadNonce, $aeadKey));   // bool(false): moved to another record

// Signatures: prove a catalogue export came from us
$keypair = sodium_crypto_sign_keypair();
$signature = sodium_crypto_sign_detached('catalogue-2026-10.csv contents', sodium_crypto_sign_secretkey($keypair));
var_dump(sodium_crypto_sign_verify_detached($signature, 'catalogue-2026-10.csv contents', sodium_crypto_sign_publickey($keypair)));   // bool(true)

<?php

declare(strict_types=1);

$key = random_bytes(32);
$iv = random_bytes(openssl_cipher_iv_length('aes-256-gcm'));        // 12 bytes, unique per message

$ciphertext = openssl_encrypt('member note', 'aes-256-gcm', $key, OPENSSL_RAW_DATA, $iv, $tag);
$plain = openssl_decrypt($ciphertext, 'aes-256-gcm', $key, OPENSSL_RAW_DATA, $iv, $tag);

var_dump($plain, strlen($tag));                                     // string(11) "member note" int(16)
var_dump(openssl_decrypt($ciphertext, 'aes-256-gcm', $key, OPENSSL_RAW_DATA, $iv, str_repeat("\0", 16)));   // bool(false)

<?php

declare(strict_types=1);

function encryptNote(string $note, #[\SensitiveParameter] string $key): string
{
    $nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES);
    return base64_encode($nonce . sodium_crypto_secretbox($note, $nonce, $key));
}

$key = getenv('NOTES_KEY') ?: sodium_crypto_secretbox_keygen();   // demo fallback; never hard-code a key
echo strlen(base64_decode(encryptNote('likes Le Guin', $key))), " bytes\n";