(Mono C#) Duplicate PHP's openssl_encrypt and openssl_random_pseudo_bytes

Demonstrates how to duplicate PHP's openssl_encrypt function. (https://www.php.net/manual/en/function.openssl-encrypt.php)

For more information, see https://www.php.net/manual/en/function.openssl-encrypt.php

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

// Duplicates thw following PHP script:

// $text = "This is a test";
// $passphrase = "my password";
// $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length("AES-256-CBC"));
// $crypted = base64_encode($iv.openssl_encrypt($text, "AES-256-CBC", $passphrase, OPENSSL_RAW_DATA, $iv));
// echo $crypted;

bool success;
Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

string text = "This is a test";
string passphrase = "my password";

// AES is a block cipher.  The IV size for any block cipher is the size of the block, which is defined by the encryption algorithm. 
// For AES, the block size is always 16 bytes, regardless of key size (i.e. 128-bits, 192-bits, or 256-bits).
// Therefore, generate 16 random bytes for the IV.
crypt.EncodingMode = "base64";
string ivBase64 = crypt.GenRandomBytesENC(16);

Debug.WriteLine("Generated IV = " + ivBase64);

// Because we're doing AES-256-CBC, the key length must be 256-bits (i.e. 32 bytes).
// Given that our passphrase is a us-ascii string that can be shorter or longer than 32-bytes, we need to 
// somehow transform the passphrase to a 32-byte secret key.  We need to know what openssl_encrypt does.
// Here's the answer from the openssl_encrypt documentation:
// 
// "If the passphrase is shorter than expected, it is silently padded with NUL characters; 
// if the passphrase is longer than expected, it is silently truncated."

// OK.... so let's pad or shorten to get a 32-byte key.
Chilkat.BinData bdKey = new Chilkat.BinData();
bdKey.AppendString(passphrase,"utf-8");

int sz = bdKey.NumBytes;
if (sz > 32) {
    bdKey.RemoveChunk(32,sz - 32);
}
else {
    bdKey.Clear();
    bdKey.AppendPadded(passphrase,"utf-8",false,32);
}

// Setup for encryption.
crypt.CryptAlgorithm = "aes";
crypt.KeyLength = 256;
crypt.SetEncodedIV(ivBase64,"base64");
crypt.SetEncodedKey(bdKey.GetEncoded("base64"),"base64");

// Encrypt and base64 encode.
string cipherText64 = crypt.EncryptStringENC(text);

// The PHP code fragment above returns the base64 encoded bytes of the IV and the encrypted text.
// So let's do that..
Chilkat.BinData bd = new Chilkat.BinData();
bd.AppendEncoded(ivBase64,"base64");
bd.AppendEncoded(cipherText64,"base64");
string result = bd.GetEncoded("base64");

Debug.WriteLine("result = " + result);

// Sample output:
// dN0vS1O0cWi5BbLAAY+NTf7bs3S27xzPf11RkG47sjs=

// Now let's decrypt from the output...

// Setup for decryption.
crypt.CryptAlgorithm = "aes";
crypt.KeyLength = 256;
crypt.SetEncodedKey(bdKey.GetEncoded("base64"),"base64");

Chilkat.BinData bdResult = new Chilkat.BinData();
bdResult.AppendEncoded(result,"base64");
crypt.SetEncodedIV(bdResult.GetEncodedChunk(0,16,"base64"),"base64");

// Remove the IV (first 16 bytes) from the result.
bdResult.RemoveChunk(0,16);
success = crypt.DecryptBd(bdResult);
string originalText = bdResult.GetString("utf-8");

Debug.WriteLine("original text = " + originalText);