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cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adv ...
and
computer security Computer security, cybersecurity (cyber security), or information technology security (IT security) is the protection of computer systems and networks from attack by malicious actors that may result in unauthorized information disclosure, t ...
, a man-in-the-middle, monster-in-the-middle, machine-in-the-middle, monkey-in-the-middle, meddler-in-the-middle, manipulator-in-the-middle (MITM), person-in-the-middle (PITM) or adversary-in-the-middle (AiTM) attack is a
cyberattack A cyberattack is any offensive maneuver that targets computer information systems, computer networks, infrastructures, or personal computer devices. An attacker is a person or process that attempts to access data, functions, or other restricte ...
where the attacker secretly relays and possibly alters the
communications Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...
between two parties who believe that they are directly communicating with each other, as the attacker has inserted themselves between the two parties. One example of a MITM attack is active
eavesdropping Eavesdropping is the act of secretly or stealthily listening to the private conversation or communications of others without their consent in order to gather information. Etymology The verb ''eavesdrop'' is a back-formation from the noun ''eaves ...
, in which the attacker makes independent connections with the victims and relays messages between them to make them believe they are talking directly to each other over a private connection, when in fact the entire conversation is controlled by the attacker. The attacker must be able to intercept all relevant messages passing between the two victims and inject new ones. This is straightforward in many circumstances; for example, an attacker within the reception range of an unencrypted Wi-Fi access point could insert themselves as a man-in-the-middle. As it aims to circumvent mutual authentication, a MITM attack can succeed only when the attacker impersonates each endpoint sufficiently well to satisfy their expectations. Most cryptographic protocols include some form of endpoint authentication specifically to prevent MITM attacks. For example,
TLS TLS may refer to: Computing * Transport Layer Security, a cryptographic protocol for secure computer network communication * Thread level speculation, an optimisation on multiprocessor CPUs * Thread-local storage, a mechanism for allocating vari ...
can authenticate one or both parties using a mutually trusted
certificate authority In cryptography, a certificate authority or certification authority (CA) is an entity that stores, signs, and issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. Thi ...
.


Example

Suppose
Alice Alice may refer to: * Alice (name), most often a feminine given name, but also used as a surname Literature * Alice (''Alice's Adventures in Wonderland''), a character in books by Lewis Carroll * ''Alice'' series, children's and teen books by ...
wishes to communicate with Bob. Meanwhile, Mallory wishes to intercept the conversation to eavesdrop and optionally to deliver a false message to Bob. First, Alice asks Bob for his
public key Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic al ...
. If Bob sends his public key to Alice, but Mallory is able to intercept it, an MITM attack can begin. Mallory sends Alice a forged message that appears to originate from Bob, but instead includes Mallory's public key. Alice, believing this public key to be Bob's, encrypts her message with Mallory's key and sends the enciphered message back to Bob. Mallory again intercepts, deciphers the message using her private key, possibly alters it if she wants, and re-enciphers it using the public key she intercepted from Bob when he originally tried to send it to Alice. When Bob receives the newly enciphered message, he believes it came from Alice. # Alice sends a message to Bob, which is intercepted by Mallory: #: Alice ''"Hi Bob, it's Alice. Give me your key."'' →     Mallory     Bob # Mallory relays this message to Bob; Bob cannot tell it is not really from Alice: #: Alice     Mallory ''"Hi Bob, it's Alice. Give me your key."'' →     Bob # Bob responds with his encryption key: #: Alice     Mallory     ← '' ob's key' Bob # Mallory replaces Bob's key with her own, and relays this to Alice, claiming that it is Bob's key: #: Alice     ← '' allory's key' Mallory     Bob # Alice encrypts a message with what she believes to be Bob's key, thinking that only Bob can read it: #: Alice ''"Meet me at the bus stop!" ncrypted with Mallory's key' →     Mallory     Bob # 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: #: Alice     Mallory ''"Meet me at the van down by the river!" ncrypted with Bob's key' →     Bob # Bob thinks that this message is a secure communication from Alice. This example shows the need for Alice and Bob to have some way to ensure that they are truly each using each other's public keys, rather than the public key of an attacker. Otherwise, such attacks are generally possible, in principle, against any message sent using public-key technology. A variety of techniques can help defend against MITM attacks.


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 detection merely shows evidence that a message may have been altered.


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 In cryptography, a key-agreement protocol is a protocol whereby two or more parties can agree on a key in such a way that both influence the outcome. If properly done, this precludes undesired third parties from forcing a key choice on the agreeing ...
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. A
public key infrastructure A public key infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to facili ...
, such as
Transport Layer Security Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securi ...
, may harden
Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...
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 In cryptography, a certificate authority or certification authority (CA) is an entity that stores, signs, and issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. Thi ...
(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 Mutual authentication or two-way authentication (not to be confused with two-factor authentication) refers to two parties authenticating each other at the same time in an authentication protocol. It is a default mode of authentication in some pr ...
, 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. 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 ZRTP (composed of Z and Real-time Transport Protocol) is a cryptographic key-agreement protocol to negotiate the keys for encryption between two end points in a Voice over IP (VoIP) phone telephony call based on the Real-time Transport Protocol. ...
), or recorded attestments such as audio/visual recordings of a public key hash 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. In a corporate environment, successful authentication (as indicated by the browser's green padlock) does not always imply secure connection with the remote server. Corporate security policies might contemplate the addition of custom certificates in workstations' web browsers in order to be able to inspect encrypted traffic. As a consequence, a green padlock does not indicate that the client has successfully authenticated with the remote server but just with the corporate server/proxy used for SSL/TLS inspection.
HTTP Public Key Pinning HTTP Public Key Pinning (HPKP) is an obsolete Internet security mechanism delivered via an HTTP header which allows HTTPS websites to resist impersonation by attackers using misissued or otherwise fraudulent digital certificates. A server uses ...
(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.
DNSSEC The Domain Name System Security Extensions (DNSSEC) are a suite of extension specifications by the Internet Engineering Task Force (IETF) for securing data exchanged in the Domain Name System (DNS) in Internet Protocol (IP) networks. The protocol ...
extends the DNS protocol to use signatures to authenticate DNS records, preventing simple MITM attacks from directing a client to a malicious
IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
.


Tamper detection

Latency examination can potentially detect the attack in certain situations, such as with long calculations that lead into tens of seconds like
hash functions A hash function is any function that can be used to map data of arbitrary size to fixed-size values. The values returned by a hash function are called ''hash values'', ''hash codes'', ''digests'', or simply ''hashes''. The values are usually ...
. 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 interference 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.


Forensic analysis

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: * IP address of the server * DNS name of the server *
X.509 In cryptography, X.509 is an International Telecommunication Union (ITU) standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, which is the basis for HTTPS, the secu ...
certificate of the server ** Whether the certificate has been self signed ** Whether the certificate has been signed by a trusted
certificate authority In cryptography, a certificate authority or certification authority (CA) is an entity that stores, signs, and issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. Thi ...
** Whether the certificate has been revoked ** Whether the certificate has been changed recently ** Whether other clients, elsewhere on the Internet, received the same certificate


Notable instances

A Stingray phone tracker is a cellular phone surveillance device that mimics a wireless carrier cell tower in order to force all nearby mobile phones and other cellular data devices to connect to it. The tracker relays all communications back and forth between cellular phones and cell towers. In 2011, a security breach of the Dutch certificate authority DigiNotar resulted in the fraudulent issuing of certificates. Subsequently, the fraudulent certificates were used to perform MITM attacks. In 2013,
Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Espoo, Finland, i ...
's
Xpress Browser Nokia Xpress (also called Xpress Browser) was a mobile browser developed by Nokia and supported by Microsoft until the end of 2015. It came loaded by default with Series 40, Asha Platform and Nokia X Software Platform. It uses the Gecko renderin ...
was revealed to be decrypting HTTPS traffic on Nokia's
proxy server In computer networking, a proxy server is a server application that acts as an intermediary between a client requesting a resource and the server providing that resource. Instead of connecting directly to a server that can fulfill a reques ...
s, giving the company
clear text In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overview With the advent of co ...
access to its customers' encrypted browser traffic. Nokia responded by saying that the content was not stored permanently, and that the company had organizational and technical measures to prevent access to private information. In 2017,
Equifax Equifax Inc. is an American multinational consumer credit reporting agency headquartered in Atlanta, Georgia and is one of the three largest consumer credit reporting agencies, along with Experian and TransUnion (together known as the "Big Th ...
withdrew its mobile phone apps following concern about MITM vulnerabilities. Other notable real-life implementations include the following: *
DSniff dSniff is a set of password sniffing and network traffic analysis tools written by security researcher and startup founder Dug Song to parse different application protocols and extract relevant information. dsniff, filesnarf, mailsnarf, msgsnarf ...
the first public implementation of MITM attacks against SSL and SSHv1 * Fiddler2 HTTP(S) diagnostic tool *
NSA The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collec ...
impersonation of
Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...
*
Qaznet Trust Certificate In 2015, the government of Kazakhstan created a root certificate which could have enabled a man-in-the-middle attack on HTTPS traffic from Internet users in Kazakhstan. The government described it as a "national security certificate". If install ...
* Superfish malware * Forcepoint Content Gateway used to perform inspection of SSL traffic at the
proxy Proxy may refer to: * Proxy or agent (law), a substitute authorized to act for another entity or a document which authorizes the agent so to act * Proxy (climate), a measured variable used to infer the value of a variable of interest in climate re ...
*
Comcast Comcast Corporation (formerly known as American Cable Systems and Comcast Holdings),Before the AT&T merger in 2001, the parent company was Comcast Holdings Corporation. Comcast Holdings Corporation now refers to a subsidiary of Comcast Corpora ...
uses MITM attacks to inject JavaScript code to 3rd party web pages, showing their own ads and messages on top of the pages * 2015
Kazakhstan man-in-the-middle attack In 2015, the government of Kazakhstan created a root certificate which could have enabled a man-in-the-middle attack on HTTPS traffic from Internet users in Kazakhstan. The government described it as a "national security certificate". If installed ...


See also

* ARP spoofing – a technique by which an attacker sends Address Resolution Protocol messages onto a local area network * Aspidistra transmitter a British radio transmitter used for World War II "intrusion" operations, an early MITM attack. * Babington Plot the plot against Elizabeth I of England, where Francis Walsingham intercepted the correspondence. *
Computer security Computer security, cybersecurity (cyber security), or information technology security (IT security) is the protection of computer systems and networks from attack by malicious actors that may result in unauthorized information disclosure, t ...
the design of secure computer systems. *
Cookiemonster attack The CookieMonster attack is a man-in-the-middle exploit where a third party can gain HTTPS cookie data when the "Encrypted Sessions Only" property is not properly set. This could allow access to sites with sensitive personal or financial informati ...
a man-in-the-middle exploit. *
Cryptanalysis Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic s ...
the art of deciphering encrypted messages with incomplete knowledge of how they were encrypted. *
Digital signature A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...
a cryptographic guarantee of the authenticity of a text, usually the result of a calculation only the author is expected to be able to perform. * Evil maid attack attack used against full disk encryption systems *
Interlock protocol In cryptography, the interlock protocol, as described by Ron Rivest and Adi Shamir, is a protocol designed to frustrate eavesdropper attack against two parties that use an anonymous key exchange protocol to secure their conversation. A further pap ...
a specific protocol to circumvent an MITM attack when the keys may have been compromised. * Key management how to manage cryptographic keys, including generation, exchange and storage. *
Key-agreement protocol In cryptography, a key-agreement protocol is a protocol whereby two or more parties can agree on a key in such a way that both influence the outcome. If properly done, this precludes undesired third parties from forcing a key choice on the agreeing ...
a cryptographic protocol for establishing a key in which both parties can have confidence. * Man-in-the-browser a type of web browser MITM *
Man-on-the-side attack A man-on-the-side attack is a form of active attack in computer security similar to a man-in-the-middle attack. Instead of completely controlling a network node as in a man-in-the-middle attack, the attacker only has regular access to the commu ...
a similar attack, giving only regular access to a communication channel. *
Mutual authentication Mutual authentication or two-way authentication (not to be confused with two-factor authentication) refers to two parties authenticating each other at the same time in an authentication protocol. It is a default mode of authentication in some pr ...
how communicating parties establish confidence in one another's identities. * Password-authenticated key agreement a protocol for establishing a key using a password. * Quantum cryptography the use of quantum mechanics to provide security in cryptography. * Secure channel a way of communicating resistant to interception and tampering. *


References


External links


Finding Hidden Threats by Decrypting SSL
(PDF). SANS Institute. {{Malware Cryptographic attacks Computer network security Transport Layer Security