(Xojo Plugin) 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.

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Dim success As Boolean
success = False

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

Dim rsa As New Chilkat.Rsa

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 Chilkat.PublicKey
success = pubKey.LoadFromString(pubKeyXml)
If (success = False) Then
    System.DebugLog(pubKey.LastErrorText)
    Return
End If

Dim privKey As New Chilkat.PrivateKey
success = privKey.LoadXml(privKeyXml)
If (success = False) Then
    System.DebugLog(privKey.LastErrorText)
    Return
End If

success = rsa.UsePublicKey(pubKey)
If (success = False) Then
    System.DebugLog(rsa.LastErrorText)
    Return
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 Boolean
usePrivateKey = False
Dim encryptedStr1 As String
encryptedStr1 = rsa.EncryptStringENC(plainText,usePrivateKey)
System.DebugLog(encryptedStr1)

// Do it again. The results are different...
Dim encryptedStr2 As String
encryptedStr2 = rsa.EncryptStringENC(plainText,usePrivateKey)
System.DebugLog(encryptedStr2)

// Now decrypt both strings, and the results are correct
// in both cases:
Dim rsa2 As New Chilkat.Rsa
success = rsa2.UsePrivateKey(privKey)
If (success = False) Then
    System.DebugLog(rsa.LastErrorText)
    Return
End If

rsa2.EncodingMode = "base64"
usePrivateKey = True

Dim decryptedStr1 As String
decryptedStr1 = rsa2.DecryptStringENC(encryptedStr1,usePrivateKey)
System.DebugLog(decryptedStr1)

Dim decryptedStr2 As String
decryptedStr2 = rsa2.DecryptStringENC(encryptedStr2,usePrivateKey)
System.DebugLog(decryptedStr2)