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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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Detect MITM with hashed session-key — Is my protocol secure?

I have the following setup: An app ("client") wants to communicate securely with a device I created ("server"). The client has the public key of the server (and a hashed password) preinstalled. I use ...
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Multilinear trapdoor commitments secure against concurrent man-in-the-middle attacks

I am trying to understand how to apply a multi-trapdoor commitments described by Gennaro and what makes them secure against a concurrent MiM attack. There are two ways to construct a multi-trapdoor ...
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How is it possible for a VPN connection to be created through the ISP?

I will be theoretical here. Let's say you want to create a VPN connection with some VPN provider. You have to agree on some key to encrypt the data. how can you get the key without your ISP knowing it?...
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105 views

Authentication and integrity

I was trying to solve this problem: Sometimes Alice needs to send a file to Bob, guaranteeing her identity and the file integrity (no confidentiality required); the two parties are sharing a secret w ...
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198 views

MD5 hash functions to prove integrity of a download

It doesn't take a lot of time on the crypto StackExchange to realise the sentiment around MD5 hash functions is poor. My questions are: If it's such a bad idea to make use of MD5 hash functions why ...
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93 views

What can I do, if my SRP password verifier was stolen?

I've got a system that works like this: ...
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1answer
52 views

ECDH vs MITM ablity to change content

We all know how DH is great, and ECDH is much greater, but only in case of Eve spying on public keys, so how can ECDH defeat the ablity of "Eve" to change the public keys between Bob and Alice with ...
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2answers
107 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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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
32 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
434 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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131 views

Digital certificate issuing man-in-the-middle attack

While obtaining digital certificate the applicant trusts the certificate authority (or registering authority) as CA is digitally certified (and applicant has CA's public key). To certify a domain ...
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85 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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3answers
136 views

Negotiate a secure connection without certificates?

I would like to have a simple experience for a user for setting up a secure connection between two computers against a MITM attack. Something like the following: A number (possibly base64) appears ...
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145 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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209 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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1answer
353 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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141 views

HMAC usage in hybrid encryption scheme

Consider the following hybrid encryption scheme (B3||4 is for concatenated IV and AES-CBC encrypted message): ------------------------------------------------------...
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2answers
371 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
201 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
610 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
66 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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1answer
457 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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515 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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778 views

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
680 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
244 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
91 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
2k 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
83 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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625 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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2k 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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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
243 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
4k 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
81 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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402 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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1answer
210 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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2answers
455 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
411 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
364 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
469 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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1answer
2k 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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1answer
2k 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
111 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
2k 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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1answer
112 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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141 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
255 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 ...