Simple Man-in-the-middle attack
 |
| An illustration of the man-in-the-middle attack |
Objective: To let you know basic Man-In-The-Middle attack [MITM]
Remark:
I have no time to find out all roles of MITM such as Alice, Bob, Eve,
Mallory, Trent and so on. If I can find it, I will post it. For the
protection I cannot tell you guys here since they might be banned those
approaches.
Suppose
Alice 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.
If Bob sends his public key to Alice, but Mallory is able to intercept
it, a man-in-the-middle attack can begin. Mallory sends a forged message
to Alice that purports to come 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 Bob originally sent 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 ← [Bob's key] Bob
Mallory
replaces Bob's key with her own, and relays this to Alice, claiming
that it is Bob's key: Alice ← [Mallory'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!" [encrypted
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!"
[encrypted with Bob's key] → Bob
Bob thinks that this message is a secure communication from Alice.
Bob goes to the van down by the river and gets stabbed by Mallory.
Alice does not know that Bob was stabbed by Mallory thinking Bob is late.
Not
seeing Bob for a while, she determines Bob decided to leave her for his
secretary, so she takes the kids and drives to her mother.
This example
[4][5] 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 protocols,
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.
[6]
A
public key infrastructure, such as
Transport Layer Security, may harden
Transmission Control Protocol
against Man-in-the-middle-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, though the default
behavior of most connections is to only authenticate the server.
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
[7]
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.
It's worth noting that 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 workstation's 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,
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
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,
[8] such as with long calculations that lead into tens of seconds like
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
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 e.g.
Wegman-Carter authentication.
[9]
Forensic analysis
Captured network traffic
from what is suspected to be an attack can be analyzed in order to
determine whether or not there was an attack and determine the source of
the attack, if any. Important evidence to analyze when performing
network forensics on a suspected attack includes:
[10]
IP address of the server
DNS name of the server
X.509 certificate of the server
Is the certificate self signed?
Is the certificate signed by a
trusted CA?
Has the certificate been
revoked?
Has the certificate been changed recently?
Do other clients, elsewhere on the Internet, also get the same certificate?
Notable instances
A notable non-cryptographic man-in-the-middle attack was perpetrated by a
Belkin wireless network router in 2003. Periodically, it would take over an
HTTP
connection being routed through it: this would fail to pass the traffic
on to destination, but instead itself responded as the intended server.
The reply it sent, in place of the web page the user had requested, was
an advertisement for another Belkin product. After an outcry from
technically literate users, this 'feature' was removed from later
versions of the router's
firmware.
[11]
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 man-in-the-middle attacks.[
citation needed]
In 2013, the
Nokia's
Xpress Browser was revealed to be decrypting HTTPS traffic on Nokia's
proxy servers, giving the company
clear text
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.
[12]
In 2017,
Equifax withdrew its mobile phone apps following concern about man-in-the-middle vulnerabilities.[
citation needed]
Other notable real-life implementations include the following:
DSniff – the first public implementation of MITM attacks against SSL and SSH
Fiddler2 HTTP(S) diagnostic tool
NSA impersonation of
Google[13]
Superfish malware
Forcepoint Content Gateway – used to perform inspection of SSL traffic at the
proxy
Comcast uses MITM attacks to inject JavaScript code to 3rd party web pages, showing their own ads and messages on top of the pages.
[14][15][1]
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 man-in-the-middle attack.
Babington Plot – the plot against Elizabeth I of England, where Francis Walsingham intercepted the correspondence.
Boy-in-the-browser – a simpler type of web browser MITM
Computer security – the design of secure computer systems.
Cryptanalysis – the art of deciphering encrypted messages with incomplete knowledge of how they were encrypted.
Digital signature
– 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 – a specific protocol to circumvent a man-in-the-middle attack when the keys may have been compromised.
Key management – how to manage cryptographic keys, including generation, exchange and storage.
Key-agreement protocol – 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 similar attack, giving only regular access to a communication channel.
Mutual authentication – 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 (while older methods rely on one-way functions).
Secure channel – a way of communicating resistant to interception and tampering.
Spoofing attack
In
cryptography and
computer security,
a man-in-the-middle attack (MITM) is an attack where the attacker
secretly relays and possibly alters the communication between two
parties who believe they are directly communicating with each other. One
example of a MITM is active
eavesdropping,
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 reception range of an unencrypted
wireless access point (
Wi-Fi[1][2]) could insert himself as a man-in-the-middle.
[3]
As an attack that aims at circumventing
mutual authentication,
or lack thereof, a man-in-the-middle attack can succeed only when the
attacker can impersonate each endpoint to their satisfaction as expected
from the legitimate ends. Most cryptographic protocols include some
form of endpoint
authentication specifically to prevent MITM attacks. For example,
TLS can authenticate one or both parties using a mutually trusted
certificate authority.
[2]
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