That video is misleading on several fronts. What you are seeing
there is actually a Diffie-Hellman key exchange in progress. The
so-called "private key" is not really a private key in the sense
of PKI. The tennis ball represents an encrypted message and when
decrypted contains what they label as the "private key" but
should have labeled as "secret key". The locks represent a
message encrypted with a public key, and the rubber gloved hands
have (unlabeled) keys which unlock those locks representing the
true private key. In public/private key systems like RSA, there
are two keys: the public key and the private key. Each key is
represented by a number. However, due to various mathematical
concepts surrounding prime numbers, their scarcity, and the
extreme difficulty of determining how to factor large numbers
composed of prime numbers, one person can hold the private key
(and NEVER expose it publicly) while allowing the public key to
be distributed as freely as they wish. Fundamental to
public/private key cryptog