Cryptography Reference
In-Depth Information
Ö
Alice gets Bob's public key, Ö.Bob
keeps his private key, P, secret.
B
A
P
S
Alice uses a symmetric method and the
secret key, S, to encrypt a message, N.
She sends the encrypted message to Bob.
B
A
P
N
Alice uses Bob's public key, Ö, to
encrypt the secret key, S, and sends the
chipper to Bob (normally together with
the above message).
A
Ö
B
P
P
Bob uses his private key, P, to decrypt
key S encrypted with Ö, and recovers S.
He then decrypts with S.
B
A
Ö
S
S
N
N
Figure 4.15:
Hybrid method for transmitting encrypted messages.
be too hard to memorize them). The low speed of the asymmetric method is
negligible thanks to the relatively short session keys (8 to 16 bytes). Or is there
a drawback after all?
There is, and we will recognize it when looking closer at Point 1 above. What
makes us so sure the public key we got really belongs to the person we think it
does? Fraudulent maneuvering is possible, indeed, and we will discuss it below.
The Man in the Middle
As is customary in cryptology, we will call the 'good conversers' Alice and
Bob, and call Mallory the 'malicious attacker'.
2
2
For the sake of simplicity, Mallory sometimes assumes the role of Eve, the eavesdropper,
in this topic.
