Charset Considerations when RSA Encrypting Strings

When encrypting strings, character encoding can be an issue. Encryption algorithms operate on binary data. If for example, your string includes a character such as é, the bytes used to represent it depend on the character encoding. In an "iso" encoding such as iso-8859-1, or in a "windows" encoding, such as "windows-1252", the é is represented by a single byte. In Unicode however, whether it's utf-8 or ucs-2, the é is represented by 2 bytes. When encrypting strings, the RSA component will first convert the string to the character encoding indicated by the Charset property. When decrypting strings, the RSA component converts from the character encoding indicated by the Charset property to the application's expected charset. In VB6 for example, this would be Unicode. In C++, it's ANSI. In Java, it's utf-8.

Download Chilkat RSA Public-Key Encryption ActiveX

Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
Set outFile = fso.CreateTextFile("output.txt", True)

set rsa = CreateObject("Chilkat.Rsa")

success = rsa.UnlockComponent("Anything for 30-day trial")
If (success <> 1) Then
    MsgBox "RSA component unlock failed"
    WScript.Quit
End If

'  RSA public key in XML format:
publicKey = "<RSAKeyValue><Modulus>of3im3mRgd2NLXIGoK6uYLg6jj0Ug2b42rnqa5Tbwz2ieFqMJqt+++x2oqLYGurlz49nt+7/785g3XYWqoka4u9c9zul6YubIjnBM72dQy7rEkEfbUxgjcxqXyjZFx+FpaxFUecLu688XEu+9UA42VKiCgcl+E7TrqnfeeYpNXc=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>"

rsa.ImportPublicKey publicKey

'  Use the utf-8 character encoding.  When encrypting, the
'  plain text is first converted to utf-8 bytes and then
'  RSA encrypted.
rsa.Charset = "utf-8"

'  Encrypt a string and return the encrypted data base64-encoded:
rsa.EncodingMode = "base64"

plainText = "éééé"

usePrivateKey = 0
encryptedStr = rsa.EncryptStringENC(plainText,usePrivateKey)
outFile.WriteLine(encryptedStr)
outFile.Close