how to encrypt and decrypt a String(Plain Text) with RSA public key in ios, swift

Question

I want to Encrypt a string(Plain Text) with my RSA public key. I have a public key, which sent from the server as a String and with that I created a RSA public key. now I want to use that key to Encrypt my text with padding PKACS12. how can I do that. I went through lots of stack overflow questions and I didn't get any success.

this is how I create the RSA public key,

let serverPublicKey = "Some text with key"

let data2 = Data.init(base64Encoded: serverPublicKey)

let keyDict:[NSObject:NSObject] = [
  kSecAttrKeyType: kSecAttrKeyTypeRSA,
  kSecAttrKeyClass: kSecAttrKeyClassPublic,
  kSecAttrKeySizeInBits: NSNumber(value: 2048),
  kSecReturnPersistentRef: true as NSObject
 ]

let publickeysi = SecKeyCreateWithData(data2! as CFData, keyDict as CFDictionary, nil)

this creates a RSA public key successfully. now I want to use this key to encrypt my another Plain Text. how can I do that.

Answer 1

Hope this will help you:

let serverPublicKey = "Some text with key"

    let data2 = Data.init(base64Encoded: serverPublicKey)

    let keyDict:[NSObject:NSObject] = [
      kSecAttrKeyType: kSecAttrKeyTypeRSA,
      kSecAttrKeyClass: kSecAttrKeyClassPublic,
      kSecAttrKeySizeInBits: NSNumber(value: 2048),
      kSecReturnPersistentRef: true as NSObject
     ]

    let publickeysi = SecKeyCreateWithData(data2! as CFData, keyDict as CFDictionary, nil)

    //Encrypt a string with the public key
            let message = "This is my message."
            let blockSize = SecKeyGetBlockSize(publickeysi!)
            var messageEncrypted = [UInt8](repeating: 0, count: blockSize)
            var messageEncryptedSize = blockSize

            var status: OSStatus!

            status = SecKeyEncrypt(publickeysi!, SecPadding.PKCS1, message, message.characters.count, &messageEncrypted, &messageEncryptedSize)

            if status != noErr {
                print("Encryption Error!")
                return
            }

Answer 2

import Foundation
import Security


struct RSA {

static func encrypt(string: String, publicKey: String?) -> String? {
    guard let publicKey = publicKey else { return nil }

    let keyString = publicKey.replacingOccurrences(of: "-----BEGIN RSA PUBLIC KEY-----\n", with: "").replacingOccurrences(of: "\n-----END RSA PUBLIC KEY-----", with: "")
    guard let data = Data(base64Encoded: keyString) else { return nil }

    var attributes: CFDictionary {
        return [kSecAttrKeyType         : kSecAttrKeyTypeRSA,
                kSecAttrKeyClass        : kSecAttrKeyClassPublic,
                kSecAttrKeySizeInBits   : 2048,
                kSecReturnPersistentRef : true] as CFDictionary
    }

    var error: Unmanaged<CFError>? = nil
    guard let secKey = SecKeyCreateWithData(data as CFData, attributes, &error) else {
        print(error.debugDescription)
        return nil
    }
    return encrypt(string: string, publicKey: secKey)
}

static func encrypt(string: String, publicKey: SecKey) -> String? {
    let buffer = [UInt8](string.utf8)

    var keySize   = SecKeyGetBlockSize(publicKey)
    var keyBuffer = [UInt8](repeating: 0, count: keySize)

    // Encrypto  should less than key length
    guard SecKeyEncrypt(publicKey, SecPadding.PKCS1, buffer, buffer.count, &keyBuffer, &keySize) == errSecSuccess else { return nil }
    return Data(bytes: keyBuffer, count: keySize).base64EncodedString()
   }
}

Use like this

var pemString = "-----BEGIN RSA PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAl/zjMK4w1XZAnpIqLeTAMW7cEUNIifP3HjmUavvc2+oPG1QjNCfxQM6LulZSl6qRim2JGxbc3yvnbMRJqch6IhJ/ysbTekVSqOjskIRGxq0pg0J8PqF3ZZQK6D7BYHi6iaJUMVV0ISB5LogJouyOWqsZyiEjgPz3jj0HIrh14Q6wPZVMpVbIwQR9nZp5gU5minseCyZfQs3PArgXgnzRPdw7Hb0/NY5OVE2Rz1SFTnda6w12SEu1IsVhVhJz1QteNrwNwJAT6WgZd+xnOZhU3Ei+EQK2SijfEGqmWNt1utJygK/0APy8w7VTol7ygbqfuHevGcg90QEXjxZKCjkXkQIDAQAB\n-----END RSA PUBLIC KEY-----"


let password = "abcdefg"
let encryptedPassword = RSA.encrypt(string: password, publicKey: pemString)
print(encryptedPassword)