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

== Defense and detection ==
MITM attacks can be prevented or detected by two means: authentication and tamper detection. Authentication provides some degree of certainty that a given message has come from a legitimate source. [[Tamper-evident technology#Computer systems|Tamper detection]] merely shows evidence that a message may have been altered and has broken integrity.

=== Authentication ===
All cryptographic systems that are secure against MITM attacks provide some method of authentication for messages. Most require an exchange of information (such as public keys) in addition to the message over a [[secure channel]]. Such protocols, often using [[key-agreement protocol]]s, have been developed with different security requirements for the secure channel, though some have attempted to remove the requirement for any secure channel at all.<ref name="Merkle 1978">{{cite journal|last1=Merkle|first1=Ralph C|title=Secure Communications Over Insecure Channels|journal=Communications of the ACM|date=April 1978|volume=21|issue=4|pages=294–299|doi=10.1145/359460.359473|quote=Received August, 1975; revised September 1977|citeseerx=10.1.1.364.5157|s2cid=6967714}}</ref>

A [[public key infrastructure]], such as [[Transport Layer Security]], may harden [[Transmission Control Protocol]] against MITM attacks. In such structures, clients and servers exchange certificates which are issued and verified by a trusted third party called a [[certificate authority]] (CA). If the original key to authenticate this CA has not been itself the subject of a MITM attack, then the certificates issued by the CA may be used to authenticate the messages sent by the owner of that certificate. Use of [[mutual authentication]], in which both the server and the client validate the other's communication, covers both ends of a MITM attack. If the server or client's identity is not verified or deemed as invalid, the session will end.<ref>Sasikaladevi, N. and D. Malathi. 2019. “Energy Efficient Lightweight Mutual Authentication Protocol (REAP) for MBAN Based on Genus-2 Hyper-Elliptic Curve.” Wireless Personal Communications 109(4):2471–88.</ref> However, the default behavior of most connections is to only authenticate the server, which means mutual authentication is not always employed and MITM attacks can still occur.

Attestments, such as verbal communications of a shared value (as in [[ZRTP]]), or recorded attestments such as audio/visual recordings of a public key hash<ref>{{cite arXiv |last=Heinrich|first=Stuart |eprint=1311.7182v1 |title=Public Key Infrastructure based on Authentication of Media Attestments |date=2013-11-28|class=cs.CR }}</ref> are used to ward off MITM attacks, as visual media is much more difficult and time-consuming to imitate than simple data packet communication. However, these methods require a human in the loop in order to successfully initiate the transaction.

[[HTTP Public Key Pinning]] (HPKP), sometimes called "certificate pinning", helps prevent a MITM attack in which the certificate authority itself is compromised, by having the server provide a list of "pinned" public key hashes during the first transaction. Subsequent transactions then require one or more of the keys in the list must be used by the server in order to authenticate that transaction.

[[Domain Name System Security Extensions|DNSSEC]] extends the DNS protocol to use signatures to authenticate DNS records, preventing simple MITM attacks from directing a client to a malicious [[IP address]].

=== Tamper detection ===
Latency examination can potentially detect the attack in certain situations,<ref>{{cite book |last1= Aziz|first1= Benjamin|last2= Hamilton|first2= Geoff |title= 2009 Third International Conference on Emerging Security Information, Systems and Technologies|chapter= Detecting Man-in-the-Middle Attacks by Precise Timing|date= 2009|pages= 81–86|doi= 10.1109/SECURWARE.2009.20|isbn= 978-0-7695-3668-2|s2cid= 18489395|chapter-url= https://researchportal.port.ac.uk/portal/files/107556/Detecting_Man-in-the-Middle_Attacks_by_Precise_Timing.pdf}}</ref> such as with long calculations that lead into tens of seconds like [[cryptographic hash function|hash functions]]. To detect potential attacks, parties check for discrepancies in response times. For example: Say that two parties normally take a certain amount of time to perform a particular transaction. If one transaction, however, were to take an abnormal length of time to reach the other party, this could be indicative of a third party's presence interfering with the connection and inserting additional latency in the transaction.

[[Quantum cryptography]], in theory, provides tamper-evidence for transactions through the [[no-cloning theorem]]. Protocols based on quantum cryptography typically authenticate part or all of their classical communication with an unconditionally secure authentication scheme. As an example [[Wegman-Carter authentication]].<ref>{{cite web|url=http://www.lysator.liu.se/~jc/mthesis/5_Unconditionally_secure_au.html|title=5. Unconditionally secure authentication|work=liu.se|first=Jörgen|last=Cederlöf}}</ref>

=== Forensic analysis ===
[[Packet capture|Captured network traffic]] from what is suspected to be an attack can be analyzed in order to determine whether there was an attack and, if so, determine the source of the attack. Important evidence to analyze when performing [[network forensics]] on a suspected attack includes:<ref>{{cite web |url=http://www.netresec.com/?page=Blog&month=2011-03&post=Network-Forensic-Analysis-of-SSL-MITM-Attacks |title=Network Forensic Analysis of SSL MITM Attacks |work=NETRESEC Network Security Blog |date=2011-03-27|access-date=2011-03-27}}</ref>
* IP address of the server
* DNS name of the server
* [[X.509]] certificate of the server
** Whether the certificate has been self signed
** Whether the  certificate has been signed by a trusted [[certificate authority]]
** Whether the certificate has been [[certificate revocation|revoked]]
** Whether the certificate has been changed recently
** Whether other clients, elsewhere on the Internet, received the same certificate