(C# UWP/WinRT) 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.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

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

Chilkat.Rsa rsa = new Chilkat.Rsa();

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

string 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>";

bool success = rsa.ImportPublicKey(publicKey);

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

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

bool usePrivateKey = false;
string encryptedStr1 = rsa.EncryptStringENC(plainText,usePrivateKey);
Debug.WriteLine(encryptedStr1);

// Do it again. The results are different...
string encryptedStr2 = rsa.EncryptStringENC(plainText,usePrivateKey);
Debug.WriteLine(encryptedStr2);

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

string decryptedStr1 = rsa2.DecryptStringENC(encryptedStr1,usePrivateKey);
Debug.WriteLine(decryptedStr1);

string decryptedStr2 = rsa2.DecryptStringENC(encryptedStr2,usePrivateKey);
Debug.WriteLine(decryptedStr2);