The message was written in 'cipher'. [=the message was coded]
She was nothing more than a 'cipher'.
a 'cipher' that can't be decoded
(..) 'Or trailing his coat and looking for a pass from some mug like me.' 'So the second night I went to the import/ export outfit 'that Tufty had set up with a cipher room hidden in the back. 'I cabled "No sale" to Mr Guillam. 'And that was that.' You were due to fly home the next day. Yes. (..)2011 Tinker Tailor Soldier Spy