Exchanging Encryption Keys
Despite centuries of evolution of symmetric key cryptography,
the fundamental problem of secure key distribution remains:
|
"How can two people (or machines) encrypt and decrypt messages using a key if
they are not sure that the key itself is secure?"
|
Diffie-Merkle-Hellman Key exchange
In 1976 Diffie and Hellman,
from Stanford University,
wrote the paper Multi-User Cryptographic Techniques,
proposing a method of exchanging keys.
The Diffie-Hellman key exchange technique enables two active
participants (who may never have met) to agree on a new, temporary,
session key with which they will exchange a message.
Moreover, anyone eavesdropping on their agreement discussion,
will not be able to further eavesdrop on the message exchange.
A simple (physical) analogy of how keys can be exchanged:
- A wants to send a key to B.
- A puts the key in a secure box and locks it with A's padlock.
- B does not have the key to A's padlock, so instead,
- B receives the box and adds B's own padlock to the box
and returns it to A.
- A removes A's padlock with A's own key and sends
the box back to B.
- B can now remove B's own padlock and remove the key
which is now shared by A and B.
The work of Diffie and Hellman was revolutionary in the way we think about
cryptography.
Previously it was 'intuitively obvious' that the key needed to encode and
decode a message needed to be the same (or trivially related).
CITS3002 Computer Networks, Lecture 12, Cryptography's role in networking, p12, 22nd May 2024.
|
CITS3002