(PHP Extension) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat PHP Downloads PHP Extension for Windows, Linux, MacOS, Alpine Linux, Solaris

<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

$pubkey = new CkPublicKey();

$sbPem = new CkStringBuilder();
$bCrlf = true;
$sbPem->AppendLine('-----BEGIN PUBLIC KEY-----',$bCrlf);
$sbPem->AppendLine('MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF',$bCrlf);
$sbPem->AppendLine('3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA',$bCrlf);
$sbPem->AppendLine('04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s',$bCrlf);
$sbPem->AppendLine('Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF',$bCrlf);
$sbPem->AppendLine('wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE',$bCrlf);
$sbPem->AppendLine('f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W',$bCrlf);
$sbPem->AppendLine('SwIDAQAB',$bCrlf);
$sbPem->AppendLine('-----END PUBLIC KEY-----',$bCrlf);

// Load the public key object from the PEM. 
$success = $pubkey->LoadFromString($sbPem->getAsString());
if ($success != true) {
    print $pubkey->lastErrorText() . "\n";
    exit;
}

// Build a small string to encrypt
$json = new CkJsonObject();
$json->UpdateString('example','123');
$json->UpdateString('hello','world');
print $json->emit() . "\n";

// This is the JSON to be RSA encrypted:  {"example":"123","hello":"world"}

// IMPORTANT: RSA encryption is only used to encrypt small amounts of data.
// RSA is only able to encrypt data to a maximum amount of your key size (2048 bits = 256 bytes) 
// minus padding / header data (11 bytes for PKCS#1 v1.5 padding, 42 bytes for OAEP).
// As a result it is often not possible to encrypt files with RSA directly. 
// RSA is also not meant for this purpose. 
// 
// If you want to encrypt more data, you can use something like:
// 1) Generate a 256-bit random keystring K
// 2) Encrypt your data with AES-CBC with K
// 3) Encrypt K with RSA
// 4) Send both to the other side 

$rsa = new CkRsa();
$rsa->put_OaepPadding(true);
$rsa->put_OaepHash('SHA-256');
$rsa->ImportPublicKeyObj($pubkey);
$rsa->put_EncodingMode('base64');

// Note: The OAEP padding uses random bytes in the padding, and therefore each time encryption happens,
// even using the same data and key, the result will be different --  but still valid.  One should not expect
// to get the same output.
$bUsePrivateKey = false;
$encryptedStr = $rsa->encryptStringENC($json->emit(),$bUsePrivateKey);
if ($rsa->get_LastMethodSuccess() != true) {
    print $rsa->lastErrorText() . "\n";
    exit;
}

print 'Result: ' . $encryptedStr . "\n";

?>