The Zhou-Gollmann protocol
n Non-Repudiation of Recipient: a can prove that b has
got the message by presenting
{fNRR .a.l.c}SkbÝ andÝ Ý{fCON .a.b.l.k}Skj
n Non-Repudiation of Origin: b can prove that a has
sent the message by presenting
{fNRO .b.l.c}SkaÝ andÝ Ý{fCON .a.b.l.k}Skj