(Swift 2) 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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func chilkatTest() {
    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    let rsa = CkoRsa()

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

    var privateKey: String? = "<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>"

    var success: Bool = rsa.ImportPublicKey(publicKey)

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

    var plainText: String? = "RSA gives different results with each call, weird but OK"

    var usePrivateKey: Bool = false
    var encryptedStr1: String? = rsa.EncryptStringENC(plainText, bUsePrivateKey: usePrivateKey)
    print("\(encryptedStr1!)")

    // Do it again. The results are different...
    var encryptedStr2: String? = rsa.EncryptStringENC(plainText, bUsePrivateKey: usePrivateKey)
    print("\(encryptedStr2!)")

    // Now decrypt both strings, and the results are correct
    // in both cases:
    let rsa2 = CkoRsa()
    success = rsa2.ImportPrivateKey(privateKey)
    rsa2.EncodingMode = "base64"
    usePrivateKey = true

    var decryptedStr1: String? = rsa2.DecryptStringENC(encryptedStr1, bUsePrivateKey: usePrivateKey)
    print("\(decryptedStr1!)")

    var decryptedStr2: String? = rsa2.DecryptStringENC(encryptedStr2, bUsePrivateKey: usePrivateKey)
    print("\(decryptedStr2!)")

}