# Tag Info

5

For P2P authentication, you can go for web of trust concept. Simply this means, if someone is trusted by people you can trust, you can also trust that unknown person. In OpenPGP, a certificate can be signed by other users who trust the association of that public key with the person or entity listed in the certificate. So trust relationships can be ...

4

You may be interested in something like the Cryptographically Generated Address (CGA) from RFC 3972. CGA is used in Secure Neighbor Discovery Protocol (SEND) of RFC 3971 to bind a public key to an IPv6 address. The basic idea of CGA is to generate part of the IPv6 address by computing a cryptographic hash over the public key. The corresponding private key ...

4

That was a bad edit to Wikipedia. The phrase "Carry-forward verification" is not a standard, well-known term in the cryptographic literature. It should not have been included in Wikipedia without a reference to something more specific. But oh well, no one is perfect, sometimes these things happen. Your request for an elaborate survey of MITM defence is ...

2

Why are there exactly $m$ values for $k$? Well, assuming $k$ is the value of the shared secret that either Alice and Bob derive, well, that's not true; there are at most $m$ possible values, however it may be fewer. There will be exactly $m$ values if $g$ is a primitive root modulo $p$; however when we use Diffie-Hellman in practice, we generally avoid ...

2

Well, as it says in your link the problem is authentication. So somehow Alice and Bob must set up an authenticated channel. One way of implementing such a channel is by Alice and Bob holding each others public verification key for a signature scheme. A CA would probably not hold a secret key for Alice and Bob. However, using a CA to get an authentic copy ...

2

Firstly, PKI makes use of a private key and a public key. The private key is known only to the user, while the public key is communicated securely via the use of certificates. To provide authentication and non-repudiation, users may sign a message with their private keys and obtain a digital signature. Any other users can verify that the signed signature is ...

2

Authentication without a central server (as trusted authority, e.g. root of a PKI) is a difficult task. The main question is, what actually defines the identity of a user and which information can be used to verify an identity claim. One idea would be to use digital signatures, where each user holds his own signing key and can verify himself by signing ...

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The question Alex linked in comments explains why authentication works to prevent a man-in-the-middle attack on Diffie–Hellman. So, whenever you can do the key exchange in an authenticated channel, you can be sure there is no MitM attack. (Assuming DH problem remains unbroken, of course.) Now, your questions: Is one solution for both Alice and Bob ...

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The problem about Man-in-the-Middle attack on Diffie-Hellman is that both sides are not confident about other side's public key (g^a and g^b). If they were sure that they have correct public key of their's friend Man-in-the-Middle attack wouldn't be possible, because MITM attack is based on the forgery of public keys by adversary! If for instance Bob and ...

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DrLecter is right. It all boils down to making sure to use the right public key. In fact this is the same for any public key cryptosystem be it RSA elGamal or ECC variants thereof. A MAC or whatever other construction local to your system won't do the job. The MAC e.g. can only make sure the last "editor" of the message knew the symmetric key the message ...

1

No, because Bob cannot know for sure who send the public key in the first place. So impersonation may still be an issue, even if man-in-the-middle attacks are not possible. If the communication is over a channel that can only be eavesdropped by Eve (i.e. Even cannot send anything to Bob within Bob knowing it is not from Alice), then this is secure. But ...

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…what if I only verify the signature of one end? Bob would not be able to know if he is looking at a signature by Eve, or if it’s a valid signature coming from Alice. In case if Eve is messing with the exchange, Eve would be able to inject her own (as it is handled non-authenticated) and Eve would be able to verify that it’s Bob on the other end (which ...

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Server distribute respective private keys to A (PrivateKeyA) and B (PrivateKeyB) and stores their public keys (PublicKeyA and PublicKeyB) within it's database. Now any of the user (eg A) generates a random session key (K) and encrypts this key with its own private key (PrivateKeyA). Since server has public key of A, it can decrypt the encrypted session key. ...

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In short: If you assume no shared secret, you can not build anything. For some theory on this, a similar assumption is formalized in the Dolev Yao model (all messages are send via the attacker, assumes perfect encryption), where no unauthenticated key exchange is possible. If you assume a shared secret, then it depends on the kind of secret to run a number ...

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