(Visual Basic 6.0) RSA Encrypt String to Binary Result and Reverse

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Demonstrates how to RSA encrypt a string to a binary result, and the reverse.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

' The RSA public key is used for encryption, and the private key for decryption.

' The public key's role is to make encryption accessible to anyone while ensuring that
' only the private key holder can decrypt the messages.
' The public key is designed to be widely distributed so anyone can use it to encrypt messages
' intended for the owner of the private key.

' Load our 2048-bit RSA public key.
Dim pubKey As New PublicKey
' In all Chilkat methods expecting a path, you pass either absolute or relative paths.
Dim success As Long
success = pubKey.LoadFromFile("qa_data/rsaKeys/myTestRsaPublic.pem")
If (success = 0) Then
    Debug.Print pubKey.LastErrorText
    Exit Sub
End If

Dim rsa As New ChilkatRsa

' Tell RSA to use the public key.
success = rsa.ImportPublicKeyObj(pubKey)

' RSA encryption is for small amounts of data, on the order of 200 bytes or less.
' The maximum number of bytes that can be RSA encrypted depends
' on the RSA key size and padding scheme (OAEP padding vs PKCS#1 v1.5 padding).
' For specific limits, see: RSA Encryption Maximum Number of Bytes

' Encrypt the utf-8 byte representation of the string.
rsa.Charset = "utf-8"

' Be Careful when Using non-us-ascii String Literals in Source Code
Dim encBytes() As Byte
encBytes = rsa.EncryptString("Élève français dîne à côté d’un café où l’on sert déjà du gâteau au chocolat et des éclairs délicieux",0)

' ------------------------------------------------------------------------------------------------------------------------
' Let's decrypt, which requires the matching private key...

' Load the matching 2048-bit RSA private key.
Dim privKey As New PrivateKey
Dim password As String
password = "secret"
success = privKey.LoadAnyFormatFile("qa_data/rsaKeys/myTestRsaPrivate.pem",password)
If (success = 0) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
End If

' Tell the RSA object to use the private key.
success = rsa.ImportPrivateKeyObj(privKey)

' Indicate that after decrypting the resultant decrypted bytes contains the utf-8 byte representation of the text.
rsa.Charset = "utf-8"
Dim originalText As String
originalText = rsa.DecryptString(encBytes,1)
If (success = 0) Then
    Debug.Print rsa.LastErrorText
    Exit Sub
End If

Debug.Print "Original text = " & originalText
Debug.Print "Success."