(C# UWP/WinRT) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

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

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

Chilkat.PublicKey pubkey = new Chilkat.PublicKey();

Chilkat.StringBuilder sbPem = new Chilkat.StringBuilder();
bool bCrlf = true;
sbPem.AppendLine("-----BEGIN PUBLIC KEY-----",bCrlf);
sbPem.AppendLine("MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF",bCrlf);
sbPem.AppendLine("3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA",bCrlf);
sbPem.AppendLine("04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s",bCrlf);
sbPem.AppendLine("Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF",bCrlf);
sbPem.AppendLine("wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE",bCrlf);
sbPem.AppendLine("f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W",bCrlf);
sbPem.AppendLine("SwIDAQAB",bCrlf);
sbPem.AppendLine("-----END PUBLIC KEY-----",bCrlf);

// Load the public key object from the PEM. 
bool success = pubkey.LoadFromString(sbPem.GetAsString());
if (success != true) {
    Debug.WriteLine(pubkey.LastErrorText);
    return;
}

// Build a small string to encrypt
Chilkat.JsonObject json = new Chilkat.JsonObject();
json.UpdateString("example","123");
json.UpdateString("hello","world");
Debug.WriteLine(json.Emit());

// This is the JSON to be RSA encrypted:  {"example":"123","hello":"world"}

// IMPORTANT: RSA encryption is only used to encrypt small amounts of data.
// RSA is only able to encrypt data to a maximum amount of your key size (2048 bits = 256 bytes) 
// minus padding / header data (11 bytes for PKCS#1 v1.5 padding, 42 bytes for OAEP).
// As a result it is often not possible to encrypt files with RSA directly. 
// RSA is also not meant for this purpose. 
// 
// If you want to encrypt more data, you can use something like:
// 1) Generate a 256-bit random keystring K
// 2) Encrypt your data with AES-CBC with K
// 3) Encrypt K with RSA
// 4) Send both to the other side 

Chilkat.Rsa rsa = new Chilkat.Rsa();
rsa.OaepPadding = true;
rsa.OaepHash = "SHA-256";
rsa.ImportPublicKeyObj(pubkey);
rsa.EncodingMode = "base64";

// Note: The OAEP padding uses random bytes in the padding, and therefore each time encryption happens,
// even using the same data and key, the result will be different --  but still valid.  One should not expect
// to get the same output.
bool bUsePrivateKey = false;
string encryptedStr = rsa.EncryptStringENC(json.Emit(),bUsePrivateKey);
if (rsa.LastMethodSuccess != true) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

Debug.WriteLine("Result: " + encryptedStr);