Editing Man-in-the-middle attack (section)

== Example ==
[[File:Man in the middle attack.svg|thumb|An illustration of the man-in-the-middle attack|220x220px]]

Suppose [[Alice and Bob|Alice]] wishes to communicate with [[Alice and Bob|Bob]]. Meanwhile, [[Alice and Bob#Mallory|Mallory]] wishes to intercept the conversation to eavesdrop (breaking confidentiality) with the option to deliver a false message to Bob under the guise of Alice (breaking non-repudiation). Mallory would perform a man-in-the-middle attack as described in the following sequence of events.

# Alice sends a message to Bob, which is intercepted by Mallory:
#: <span style="color:green;">Alice</span> ''"Hi Bob, it's Alice. Give me your key."'' → &nbsp; &nbsp; <span style="color:red;">Mallory</span> &nbsp; &nbsp; <span style="color:green;">Bob</span>
# Mallory relays this message to Bob; Bob cannot tell it is not really from Alice:
#: <span style="color:green;">Alice</span> &nbsp; &nbsp; <span style="color:red;">Mallory</span> ''"Hi Bob, it's Alice. Give me your key."'' → &nbsp; &nbsp; <span style="color:green;">Bob</span>
# Bob responds with his encryption key:
#: <span style="color:green;">Alice</span> &nbsp; &nbsp; <span style="color:red;">Mallory</span> &nbsp; &nbsp; ← ''[Bob's key]'' <span style="color:green;">Bob</span>
# Mallory replaces Bob's key with her own, and relays this to Alice, claiming that it is Bob's key:
#: <span style="color:green;">Alice</span> &nbsp; &nbsp; ← ''[Mallory's key]'' <span style="color:red;">Mallory</span> &nbsp; &nbsp; <span style="color:green;">Bob</span>
# Alice encrypts a message with what she believes to be Bob's key, thinking that only Bob can read it:
#: <span style="color:green;">Alice</span> ''"Meet me at the bus stop!" [encrypted with Mallory's key]'' → &nbsp; &nbsp; <span style="color:red;">Mallory</span> &nbsp; &nbsp; <span style="color:green;">Bob</span>
# However, because it was actually encrypted with Mallory's key, Mallory can decrypt it, read it, modify it (if desired), re-encrypt with Bob's key, and forward it to Bob:
#: <span style="color:green;">Alice</span> &nbsp; &nbsp; <span style="color:red;">Mallory</span> ''"Meet me at the park!" [encrypted with Bob's key]'' → &nbsp; &nbsp; <span style="color:green;">Bob</span>
# Bob thinks that this message is a secure communication from Alice.
This example shows the need for Alice and Bob to have a means to ensure that they are truly each using each other's public keys, and not the public key of an attacker.<ref>{{Cite web|url=https://crypto.stackexchange.com/questions/31224/mitm-on-rsa-public-key-encryption|title=diffie hellman - MiTM on RSA public key encryption|website=Cryptography Stack Exchange}}</ref> Otherwise, such attacks are generally possible, in principle, against any message sent using public-key technology.