I am currently reading Engineering Security by Peter Gutmann, on page 7 he states:
proper mutual authentication is quite different from unilateral authentication in both directions
He references What is authentication by Dieter Gollmann which is a transcript of a discussion. The relevant part here is:
Next point, if you scan the literature on entity authentication you will find, starting around 1991, comments that mutual authentication is something different from unilateral authentication going both ways.
Unfortunately I cannot follow the transcribed discussion. Can you explain the difference between bilateral authentication and double unilateral authentication both ways? Why is double unilateral authentication not sufficient?