(Swift 3,4,5...) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

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

    let pubkey = CkoPublicKey()!

    let sbPem = CkoStringBuilder()!
    var bCrlf: Bool = true
    sbPem.appendLine("-----BEGIN PUBLIC KEY-----", crlf: bCrlf)
    sbPem.appendLine("MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF", crlf: bCrlf)
    sbPem.appendLine("3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA", crlf: bCrlf)
    sbPem.appendLine("04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s", crlf: bCrlf)
    sbPem.appendLine("Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF", crlf: bCrlf)
    sbPem.appendLine("wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE", crlf: bCrlf)
    sbPem.appendLine("f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W", crlf: bCrlf)
    sbPem.appendLine("SwIDAQAB", crlf: bCrlf)
    sbPem.appendLine("-----END PUBLIC KEY-----", crlf: bCrlf)

    // Load the public key object from the PEM. 
    var success: Bool = pubkey.load(from: sbPem.getAsString())
    if success != true {
        print("\(pubkey.lastErrorText!)")
        return
    }

    // Build a small string to encrypt
    let json = CkoJsonObject()!
    json.update("example", value: "123")
    json.update("hello", value: "world")
    print("\(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 

    let rsa = CkoRsa()!
    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.
    var bUsePrivateKey: Bool = false
    var encryptedStr: String? = rsa.encryptStringENC(json.emit(), bUsePrivateKey: bUsePrivateKey)
    if rsa.lastMethodSuccess != true {
        print("\(rsa.lastErrorText!)")
        return
    }

    print("Result: \(encryptedStr!)")

}