PHP Extension Requires Chilkat v11.6.0+

Argon2 Key Derivation with a Secret (Pepper), AD, and Encodings

Demonstrates the optional Argon2 options for Crypt2.Argon2DeriveKey: secret (a pepper), ad (associated data), the encoding member and its per-member overrides saltEncoding/secretEncoding/adEncoding, passwordCharset, and maxMemoryKb.

Background. A pepper is a secret value held by the application and not stored with the hash, so a stolen hash database cannot be attacked without it. The encoding members control how the salt, secret, and ad text are interpreted as bytes (base64 by default; utf-8 uses the characters themselves). maxMemoryKb is a guard against an unreasonable memory cost.

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<?php

include("chilkat.php");

$success = false;

$crypt = new CkCrypt2();

//  The password should come from a secure source rather than being hard-coded.
$password = 'correct horse battery staple';

//  Build the Argon2 options JSON, this time using the optional secret, ad, and encoding members.
//    secret         the RFC 9106 secret value K, often called a "pepper": a key held by the
//                   application and NOT stored with the hash, so a stolen hash database cannot be
//                   attacked without it.
//    ad             optional associated data X: additional non-secret data bound into the derivation.
//    encoding       how salt, secret, and ad are encoded (default base64).  Per-member overrides are
//                   saltEncoding, secretEncoding, and adEncoding.
//    passwordCharset  the charset the password is converted to before use (default utf-8).
//    maxMemoryKb    a guard (not an Argon2 parameter) refusing to allocate more than this many KB;
//                   default 2097152 (2 GB).
$json = new CkJsonObject();

//  The salt is provided here as hex, overriding the default base64 for just this member.
$json->UpdateString('salt','0102030405060708090a0b0c0d0e0f10');
$json->UpdateString('saltEncoding','hex');

//  The pepper is supplied as UTF-8 text (its own characters are the bytes).
$json->UpdateString('secret','application-wide-pepper');
$json->UpdateString('secretEncoding','utf-8');

//  Associated data, supplied as UTF-8 text.
$json->UpdateString('ad','user-id-42');
$json->UpdateString('adEncoding','utf-8');

$json->UpdateString('passwordCharset','utf-8');
$json->UpdateInt('maxMemoryKb',1048576);
$json->UpdateInt('keyLen',32);

$bdKey = new CkBinData();
$success = $crypt->Argon2DeriveKey($password,$json->emit(),$bdKey);
if ($success == false) {
    print $crypt->lastErrorText() . "\n";
    exit;
}

$keyHex = $bdKey->getEncoded('hex');
if ($bdKey->get_LastMethodSuccess() == false) {
    print $bdKey->lastErrorText() . "\n";
    exit;
}

print 'Derived key: ' . $keyHex . "\n";

?>