It's a secret (15)

Surprisingly there is a way of passing a message without the need to pass a key - and it's been known about for some time.  It's called the "three pass method" and goes like this - we'll use the Vigenère system as an example.  I choose a keyword - I'll use "turkey" again, but I keep this to myself. B - the person I am sending the message to also chooses a keyword - let's say "spoken" and also keeps this to themselves.  Right, let's make the message "get out now".  I now encrypt this using my keyword - turkey. If you're unsure how to do this, look back to number 10 in this series.  So this comes out as ZYK YYR GIN and this is what I send to B.  Means nothing to them of course, because they don't know my keyword, but what they do is encrypt what I sent them (ZYK YYR GIN) using their keyword - spoken.  The result is RNY ICE YXB and they send this back to me.  I now decrypt this using my keyword (turkey).  That's to say I look on the T line for the letter R and then follow that up to the top line and note that letter, then I do the same for the letter N on the U line, then Y on the R line and so on.  What I end up with is YTH YYG FDK.  I send this back to B who now decrypts this using their keyword - spoken, and ends up with GET OUT NOW.  So, message passed and I kept my keyword to myself as did B.  So where's the problem?  Is there a problem?  Watch this space.