Questions tagged [man-in-the-middle]

A man-in-the-middle (MITM) attack is an active attack where the attacker is able to interpose himself between the sender and receiver. The attacker may monitor and/or modify some or all of the messages sent between the two endpoints.

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165 views

Transmit half the bits of the $g^a$ and $g^b$ as MITM countermeasure in DH key exchange?

I remember this trick from one of my crypto courses way back then, but I can't find the details, and I'm unable to figure out the logic behind it. I'm talking about a countermeasure to the MITM ...
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1answer
102 views

Is it Possible to Generate a Duplicate DH Session Key from 2 Pairs of DH Keys?

This might sound pointless at first, but I want to know if it's computationally feasible to generate the same resulting session key in 2 different DH key exchanges. The purpose would be for a man-in-...
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82 views

Is it impossible to have a decentralized service using email addresses as login?

Let's say we have a decentralized service S distributed on a network of 1000 nodes/servers. Is it possible to have a registration/sign up scheme using email address ...
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1answer
1k views

Man-in-the-middle attack on Diffie-Hellman with shared public keys?

Is it correct to say if the public key is known to all users beforehand, Diffie-Hellman key exchange is not vulnerable to man in the middle attack? Sample key exchange ( assuming all users public ...
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1answer
4k views

What are the problems of IKEv1 aggressive mode (compared to IKEv1 main mode or IKEv2)?

I would like to seek confirmation/clarification of the following statements about IKE: IKEv1 aggressive mode is supposed to be “insecure” if used with PSK. But as far as I can see, correct (or more ...
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38 views

Organizational Internal Man In The Middle Scenario

Question. I'm a software developer. I design and write secured systems for my customer. My customer recently downward directed that all traffic to/from my server be routed through a new appliance. I ...
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1answer
674 views

MITM defense in Diffie-Hellman protocol

Let's consider that Alice and Bob both know a shared secret $secret$ and don't know each other DH public keys. They want to authenticate each other and their keys using only $secret$. Let's also ...
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167 views

Is the “Pico” alternative to passwords vulnerable to man-in-the-middle?

Maybe someone has already heard about "Pico" by Frank Stajano. In short: It is a model for an alternative for using passwords for authentication and seems to be very interesting. Regarding the paper, ...
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Prevent MITM attack while encrypting data by using ElGamal ECC?

I am using ElGamal ECC to encrypt my plain text data. I want to ensure that my data is safe from a Man-In-The-Middle attack. What methodology I can adopt to achieve this goal? How can we prevent a ...
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2answers
263 views

Securing an end-to-end encrypted cloud based address book

I am analyzing an existing end-to-end encrypted, cloud based service (e.g. email, file storage or chat) which also has a public cloud based address book (for managing contacts) so that users of the ...
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172 views

HMAC usage in hybrid encryption scheme [duplicate]

Consider the following hybrid encryption scheme (B3||4 is for concatenated IV and AES-CBC encrypted message): ------------------------------------------------------...
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2answers
795 views

Does DTLS in WebRTC protect from active Man-in-the-Middle?

I wonder if it does. It seems to me that there is no way for participants to authenticate each other securely. There are, though, signaling servers, but I don't think that they are capable of key ...
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1answer
296 views

SRP and compromised verifier [closed]

Let's assume that attacker knows the verifier so now the attacker can commit a Man-in-the-Middle (MitM) attack: Client sends A to server; MitM takes it and sends B to client. As the MitM knows the ...
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1answer
762 views

Why is SRP considered to be resistant to MITM attack?

Why is SRP considered to be resistant to MITM attack? Documentation says A man-in-the-middle attack, which requires an attacker to fool both sides of a legitimate conversation, cannot be carried ...
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1answer
83 views

Why are some websites seemingly immune to self-signed certificate MitM attacks?

I recently did an experiment using MitM to gain account information (username and password) while accessing websites. I used two PCs in the scenario; one as the target, running Internet Explorer, and ...
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901 views

how to get secret keys in xor?

1) a = b ⊕ s1 2) b = a ⊕ s1 3) b ⊕ s2 = c Is there a way to find s1 and s2 if we know many different values of a and c? 4) a1 = b1 ⊕ s1 5) a1 ⊕ s1 ⊕ s2 = c1 I think it is possible if we analysis ...
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2k views

Using a single key pair for man-in-the-middle attack on Diffie-Hellman

Assume that a man-in-the-middle attack on the Diffie-Hellman key exchange protocol is possible, for which the adversary generates two public–private key pairs for the attack. Could the same attack be ...
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How can I attack a Triple-Block cipher with 2 keys (like 3DES) with a cost of ≤ 2⁵⁶

I am trying to solve something and I have but I have no idea anymore. Maybe anyone of you has an idea/solution/hint. Given is a block cipher $F$ with key length $n$. It looks like this: $$c = ENC_{k1}...
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1answer
887 views

In Diffie-Hellman, can everything be sent in plaintext?

I think my limited understanding of DH might be messed up - what's wrong with this scenario? C wants to connect to S. C has an ECDSA public key that it trusts belongs to S. Here's what happens: C ...
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1answer
350 views

Proof that any key exchange protocol is vulnerable to MitM attacks in the absence of shared information or trust

Today I realised that every key exchange protocol I know, without a priori any shared information or trust relations (i.e. any ability to sign anything), is utterly broken by an active man in the ...
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AES CBC Initialization vector - Security issues [duplicate]

I have 2 questions regarding security issues related to initialization vectors used in AES CBC Consider that I'm using a sequence number (which increments with every encryption) as an initialization ...
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1answer
114 views

Is there a way to inercept encrypted https connections by mimicking a cert authority?

In this video, it is shown how encryption can be theoretically intercepted without the client noticing it. In short something in between the connection could make a handshake with the requested ...
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1answer
4k views

How does Bluetooth pairing (SSP with numeric comparison) work?

I have a question concerning the pairing of two Bluetooth devices using Simple Secure Pairing with numeric comparison. The NIST document I am looking at states on page 14: Numeric Comparison was ...
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3answers
95 views

Is there a method/protocol to validate a self-signed certificate by comparing a shortened hash?

I'm working on a solution where an iPad should connect to a server software running on a laptop using TLS with a self-signed certificate that was automatically generated on the laptop during the ...
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1k views

Diffie-Hellman combined with DSA/RSA

we have learned Diffie-Hellman, RSA and DSA (Digital Signature Algorithm) in university. Because DH is vulnerable of Man-in-the-Middle we had the task to program the DH combined with RSA to protect ...
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1answer
4k views

ECDH Man-in-the-middle active attack

We have Alice and Bob. The man in the middle can manipulate(remove, add something etc.) A sent from Alice and B sent from Bob, how can he figure out what the common key K(A,B) is, without knowing kpr(...
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3answers
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Is this Diffie-Hellman key exchange variant vulnerable to man-in-the-middle attacks?

As we all know, the Diffie-Hellman key exchange protocol without authentication is vulnerable to a man-in-the-middle attack. And if we use STS(Station-to-Station protocol) instead, it would be secure. ...
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1answer
158 views

Attack on key exchange with authentication

Suppose the honest parties - Alice and Bob - exchange public key in person/via telephone so that attacker can only eavesdrop on the line. Alice has hashed the public key using a collision resistance ...
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1answer
436 views

What is the impact of a server not fully verifying the data in the Client Finished packet of a TLS connection?

F5 BIG-IP devices suffer from a vulnerability in which not all bytes of the Finished packet in a TLS connection are validated. The sort-of technical description can be found here. F5 don't consider it ...
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1answer
420 views

Government root SSL certificate possible vulnerabilities [closed]

I'm writing an article about new government law in Kazakhstan. The law was accepted in December, but now one of our providers announced information for small and medium business how to install ...
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1answer
974 views

Key exchange and man in the middle issue. Secure solution

I am trying to design MiTM protected key exchange algorithm. For instance I am using RSA asymmetric keys. Alice and Bob respectively have each their own pair of keys. And they should be able to ...
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1answer
8k views

What is difference between meet in the middle attack and man in the middle attack?

From my understanding man-in-the middle attack works as follow: Alice and Bob agreed to use Diffie-Hellman using $a$ and $q$. Alice sends $Y_A$. Before it reaches Bob, Charlie ...
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1answer
92 views

Can the original message be retrieved from a public/private key signature?

When I sign a message (which has potentialy low entropy) using a private key and I send it without the original message, can the original message be retrieved from the signature(s)? I want to prove – ...
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0answers
468 views

MITM Attack on Key Exchange Protocols

I was doing research on this attack and I am wondering, why is Diffie-Hellman always associated with such an attack? ​ Aren't other public key cryptography schemes vulnerable to the same kind of ...
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2answers
1k views

Does key authentication in SSH protect from MitM?

How do cryptography in SSH(2) work (secure channel establishment, authentication)? Does key authentication in SSH(2) protect from MitM by providing authentication and integrity and why?
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1answer
329 views

How can one protect against a Man In The Middle attack during key exchange without using certificates?

Besides using a certificate to defend against a man in the middle attack during a key exchange, what methods can be used?
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938 views

Curve25519 - Alice can decrypt her own message to Bob?

I'm developing an application with multiple clients and one server. All clients will have the same hard-coded Curve25519 key pair as well as the server's public key. The server will have its own key ...
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1answer
717 views

Do ECDH and ECDSA combined solution provide an authenticated protocol exchange solution in MCU environment?

I'm working on a project in MCU (micro controller) environment with GPRS connection to exchange data securely with the cloud. The encryption algorithm has been selected to use AES. I did some search ...
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1answer
805 views

How does the small n attack work?

I'm studying the Lamport's Hash one-time password scheme. This is the scheme: Alice wants to authenticate herself to Bob from a workstation that knows nothing about her. Alice only knows her ...
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4answers
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Diffie-Hellman and man-in-the-middle attacks

See here for the man-in-the-middle attack on Diffie-Hellman that I'm concerned about: What is Diffie-Hellman? How do we combat this? I have two questions: Is one solution for both Alice and Bob just ...
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1answer
8k views

What is a man-in-the-middle attack (for instance in Diffie-Hellman)?

I'm new to cryptography and I just started learning about the Diffie-Hellman key agreement. I read that this system is vulnerable to a man-in-the-middle attack when used alone. What kind of attack is ...
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1answer
135 views

possible MITM attack against servers that used to support weak DH?

from reading the TLS 1.1 RFC, it looks like it would be possible to break a previously recorded TLS <1.2, 512-bit DHE ServerKeyExchange and then send it (unmodified, with the original, valid ...
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1answer
5k views

Is there a need to encrypt data when send over https? [closed]

I was monitoring web traffic from my Android mobile using Man in the middle proxy. I installed certificate signed from my server in my mobile and I could see all applications sending sensitive ...
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0answers
190 views

Is it possible to perform one-way Diffie-Hellman MITM?

Here's something that is bugging me recently: suppose that me and my friend establish an OTR session and - as a result of that - DH key exchange is performed. My friend verifies my key, but I cannot ...
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2answers
273 views

DHE key exchange. Is it really secure?

Context I recently came across a video on the net showing the process of key exchange in Diffie Hellmann. Alice and Bob want to communicate. Eve is the (wo)man in the middle. This video is the basis ...
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27k views

Why is TLS susceptible to protocol downgrade attacks?

A recent blog post from Ivan Ristić (expert extraordinaire on all things SSL) says: all major browsers are susceptible to protocol downgrade attacks; an active MITM can simulate failure conditions ...
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3answers
5k views

How to perform authentication without central server in P2P?

How can one be sure that the man who you're talking with is the one who you think he is? i.e. How can one perform authentication in P2P network without a central trust server or Certificate Authority? ...
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1answer
217 views

DH key exchange with only one end authenticated

We know there is a man in the middle vulnerability with unauthenticated DH key establishment. And the way to negate that is to use authenticate the keys used. But what if I only verify the signature ...
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1answer
138 views

Key exchange if forward secrecy is not an issue

Let's say that we have a cryptosystem where Forward Secrecy and Man-In-The-Middle attacks are not an issue, purely hypothetically. Would it be correct for a key exchange with any given public-key ...
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2answers
278 views

How can A pass a message to B, while preventing a third party from sniffing infos?

$A$ has a message that he wants to send to $B$, without a third party being able to learn the contents of the original message. $A$ encrypts the message and sends it to a server. The server decrypts ...