Xojo Plugin

RSA Decrypt using Private Key on Smartcard or USB Token via Apple Keychain

See more Apple Keychain Examples

RSA decryption using a certificate's private key located on a hardware token or smartcard via the Apple Keychain.

Note: This example requires Chilkat v10.1.2 or greater.

Xojo Plugin

Dim success As Boolean
success = False

// Beforehand, we generated a 256-bit AES key, RSA encrypted, and saved to a file as in this example:
// Generate a Random 256-bit AES Key and RSA Encrypt

// The RSA public key used to encrypt in the above example was obtained from the Apple Keychain
// like this:
// Export a Public Key from USB Token or Smartcard using the Apple Keychain

// This example will load the encrypted data and will RSA decrypt using the 
// private key of a certificate on a USB token (or smart card) via the Keychain.
// You can list the Keychain certificates on hardware tokens using the following example:
// Apple Keychain - List Certs on Smartcards and USB Tokens

// Get the RSA encrypted data to be decrypted.
Dim bd As New Chilkat.BinData
// In all Chilkat methods expecting a path, you can pass either absolute or relative paths.
success = bd.LoadFile("rsaEncrypted/myAes.key")
If (success = False) Then
    System.DebugLog("Failed to load the encrypted AES key.")
    Return
End If

// Load the certificate having the private key from the Apple Keychain
// On MacOS and iOS, the LoadByCommonName function will search the Apple Keychain for the matching certificate.
Dim cert As New Chilkat.Cert

// To potentially prevent the PIN dialog from being displayed,
// we'll need to provide the USB token (or smart card) PIN
// Note: It might not be possible to prevent the PIN dialog from being displayed
// 
cert.SmartCardPin = "123456"

success = cert.LoadByCommonName("Test 2048 bit RSA")
If (success = False) Then
    System.DebugLog(cert.LastErrorText)
    Return
End If

Dim rsa As New Chilkat.Rsa

// Specify we wish to use the certificate's private key for decryption.
success = rsa.SetX509Cert(cert,True)
If (success = False) Then
    System.DebugLog(rsa.LastErrorText)
    Return
End If

// RSA Decrypt
rsa.VerboseLogging = True
success = rsa.DecryptBd(bd,True)
If (success = False) Then
    System.DebugLog(rsa.LastErrorText)
    Return
End If

// The contents of bd are now decrypted.
System.DebugLog("Num bytes after decryption: " + Str(bd.NumBytes))

// Some additional notes:
// 
// If using a Yubikey token, the certificate must be installed in the Key Management slot.
// The Digital Signature slot is for RSA keys to be used for signing, 
// and the Key Management slot is for RSA keys to be used for decrypting.
// 

// If you try to use the RSA key from the Digital Signature slot, you'll get an error such as this:

// The operation couldn't be completed. 
// (OSStatus error -50 - algid:encrypt:RSA:PKCS1: algorithm not supported by the key 
// <SecKeyRef:('com.apple.pivtoken:AF7172EB60DDCBF1D28459AE24398E11') 0x600001ecca90>)