(Classic ASP) 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.

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ActiveX for 32-bit and 64-bit Windows

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<%
set rsa = Server.CreateObject("Chilkat_9_5_0.Rsa")

success = rsa.UnlockComponent("Anything for 30-day trial")
If (success <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( "RSA component unlock failed") & "</pre>"
    Response.End
End If

'  RSA public key in XML format:
publicKey = "<RSAPublicKey><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>"

privateKey = "<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>"

success = rsa.ImportPublicKey(publicKey)

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

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

usePrivateKey = 0
encryptedStr1 = rsa.EncryptStringENC(plainText,usePrivateKey)
Response.Write "<pre>" & Server.HTMLEncode( encryptedStr1) & "</pre>"

'  Do it again. The results are different...
encryptedStr2 = rsa.EncryptStringENC(plainText,usePrivateKey)
Response.Write "<pre>" & Server.HTMLEncode( encryptedStr2) & "</pre>"

'  Now decrypt both strings, and the results are correct
'  in both cases:
set rsa2 = Server.CreateObject("Chilkat_9_5_0.Rsa")
success = rsa2.ImportPrivateKey(privateKey)
rsa2.EncodingMode = "base64"
usePrivateKey = 1

decryptedStr1 = rsa2.DecryptStringENC(encryptedStr1,usePrivateKey)
Response.Write "<pre>" & Server.HTMLEncode( decryptedStr1) & "</pre>"

decryptedStr2 = rsa2.DecryptStringENC(encryptedStr2,usePrivateKey)
Response.Write "<pre>" & Server.HTMLEncode( decryptedStr2) & "</pre>"

%>
</body>
</html>