Equivalence of
Definitions
• DEF1 㱻 DEF2
• If plain-space = cipher-space = key-space:
DEF1 㱻 DEF2 㱻 DEF3
• Perfect secrecy refers to all definitions
THM: Shannon secrecy and message
ndistinguishability are equivalent. When
restricting to key ambiguity
s equivalent as well.
LEMMA: implies not perfectly secret.
|P| = |C| = |K |
|K | < |P|