(Visual Basic 6.0) RSA Encryption -- Same Key Different Results

The RSA encryption algorithm produces different results for each call, even when encrypting the same data with the same key. Decryption however, will produce the correct results. This example demonstrates.

*** The reason this occurs is that RSA encryption uses PKCS1 v1.5 padding, and this padding scheme uses random bytes. It is random bytes in the padding that causes the result to be different each time.

Note: This example requires Chilkat v11.0.0 or greater.

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

Dim success As Long
success = 0

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

Dim rsa As New ChilkatRsa

Dim pubKeyXml As String
pubKeyXml = "<RSAPublicKey><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>"

Dim privKeyXml As String
privKeyXml = "<RSAKeyValue><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent><P>4cpW9fvG99Jsz8/AO7PDHTl+pPRAglksrR2kClLV2g9DEeFe/bvmCxLUgMCJ+0eGQ1zA6aA7McKr13zTQ7jKpQ==</P><Q>4cCS/kFlq/P1ExF37Fkh4pCodOEGutepLEG7Q/KljT3ZGlAY+2l8fGu4f+hrkUuGoFl7NOMaJflULoPIgQaq/Q==</Q><DP>lkjcSsvzqh3YKRXJiLNkyf3rypV8noYGU4+oEOsDxilkZfFRDafUPUiiQrRk4ui/d/SzvozU+ZDuWfaOk8PatQ==</DP><DQ>SYCD25i7W8Mwdibn3uIecEAdOQDTSh5RjIFSUYs9b8FFYJXXrHPp/jCsf6jS7RmkGa1Iui1/JAIL8KEjtS7QmQ==</DQ><InverseQ>EDAJa3TpNdPQ3GIdBpnTgFTQY5A60DcszsUW/iCYoXQdPVJ9BLBxVTe9jiLzGuNuzLkVBwQlCy0Bf84hACRV9A==</InverseQ><D>cMFdDYKkddlRNczaugOmOH8b1egpx2liSPs6GYZ2gFObAXJiPK8m+r6c2ckls7hrlUP0DZhi4cG6Tn7xANb0Ek17P7QquVhQYOmFy/YHzm+IJbcwwq7pJHhZBhtcjyXqfUZ+BADGE//GQbrSVwVltpOj5KcxG88NAprLn2MMxfE=</D></RSAKeyValue>"

Dim pubKey As New PublicKey
success = pubKey.LoadFromString(pubKeyXml)
If (success = 0) Then
    Debug.Print pubKey.LastErrorText
    Exit Sub
End If

Dim privKey As New PrivateKey
success = privKey.LoadXml(privKeyXml)
If (success = 0) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
End If

success = rsa.UsePublicKey(pubKey)
If (success = 0) Then
    Debug.Print rsa.LastErrorText
    Exit Sub
End If

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

Dim plainText As String
plainText = "RSA gives different results with each call, weird but OK"

Dim usePrivateKey As Long
usePrivateKey = 0
Dim encryptedStr1 As String
encryptedStr1 = rsa.EncryptStringENC(plainText,usePrivateKey)
Debug.Print encryptedStr1

' Do it again. The results are different...
Dim encryptedStr2 As String
encryptedStr2 = rsa.EncryptStringENC(plainText,usePrivateKey)
Debug.Print encryptedStr2

' Now decrypt both strings, and the results are correct
' in both cases:
Dim rsa2 As New ChilkatRsa
success = rsa2.UsePrivateKey(privKey)
If (success = 0) Then
    Debug.Print rsa.LastErrorText
    Exit Sub
End If

rsa2.EncodingMode = "base64"
usePrivateKey = 1

Dim decryptedStr1 As String
decryptedStr1 = rsa2.DecryptStringENC(encryptedStr1,usePrivateKey)
Debug.Print decryptedStr1

Dim decryptedStr2 As String
decryptedStr2 = rsa2.DecryptStringENC(encryptedStr2,usePrivateKey)
Debug.Print decryptedStr2