B4X

Duplicate PHP's openssl_encrypt and openssl_random_pseudo_bytes

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Demonstrates how to duplicate PHP's openssl_encrypt function. (https://www.php.net/manual/en/function.openssl-encrypt.php) B4X

Dim success As Boolean = False

'  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;

Dim crypt As ChilkatCrypt2
crypt.Initialize("crypt")

Dim text As String = "This is a test"
Dim passphrase As String = "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"
Dim ivBase64 As String = crypt.GenRandomBytesENC(16)

Log("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.
Dim bdKey As ChilkatBinData
bdKey.Initialize
bdKey.AppendString(passphrase, "utf-8")

Dim sz As Int = bdKey.NumBytes
If sz > 32 Then
    bdKey.RemoveChunk(32, sz - 32)
Else
    bdKey.Clear
    bdKey.AppendPadded(passphrase, "utf-8", False, 32)
End If


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

'  Encrypt and base64 encode.
Dim cipherText64 As String = 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..
Dim bd As ChilkatBinData
bd.Initialize
bd.AppendEncoded(ivBase64, "base64")
bd.AppendEncoded(cipherText64, "base64")
Dim result As String = bd.GetEncoded("base64")

Log("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")

Dim bdResult As ChilkatBinData
bdResult.Initialize
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)
Dim originalText As String = bdResult.GetString("utf-8")

Log("original text = " & originalText)