saving .txt securely on a device

Question

How does one securely save .txt file into ios device? I don't want the user to manipulate it with tools such as iExplorer or similar. My code so far is just basic data writing in ApplicationSupportDirectry and it look like this:

///writing to file:

do{
try stringFile.writeToFile(filePath, atomically: false, encoding: NSUTF8StringEncoding)

}catch{}

Answer 1

Encrypt it when creating / updating the file, decrypt it when reading the file. Store the encryption key in the keychain and you'll be safer than plaintext. Documentation about symmetric encryption which is available to iOS and OSX.