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4

In the question as it stands now, nothing prevents Eve to relay Do you have a cat? to Bob, get the answer A = Yes by testing A for Yes or No against hash(e_bob+A) obtained from Bob, then send hash(e_alice+A) to Alice and defeat the protocol. In a now-gone comment, it was added that we should use "strong values" for A; only Q is sent, plain A is never ...


2

If you ask about the protocol itself, as a theoretical construct, then it is safe. In theory it indeed provides all the feature that it promises. And now for the "but..." part. When you use a protocol to communicate, you are actually using one implementation of the protocol. The implementation tries to do exactly what the protocol says. However you can ...


2

Suppose Alice has never met Bob before—never in her life heard of this ‘Bob’ personage. Bob initiates a chat with Alice over a Jabber server, which facilitates (a) sending the messages along, and (b) giving Alice and Bob each others' public keys for the first time. They do a Diffie–Hellman key agreement, of course, so that a passive eavesdropper has no ...


2

The security properties of OTR and OMEMO are roughly the same. Both are vulnerable to man-in-the-middle attacks which means an active attacker that has access to the server(s) intercepts all messages and key exchanges and basically pretends to be the other contact to both parties involved. So instead of a session going directly from you to your contact (end-...


1

The attack you are referring to is called an offline dictionary attack, which checks all possible values against a given transcript. However, the typical security notion for the socialist millionaires problem should forbid this attack. In fact, designing a protocol which is secure "except for offline dictionary attacks" is trivial: both players simply hash ...


1

If Alice and Bob have no relevant secret knowledge not known to eve which controls the communication channel between them, it is impossible to create a seecure communication channel. Any protocol used, including diffie hellman, double ratchet socialist millioner or anything else can still be used with a MITM attack. Eve takes the role of Bob when talking ...


1

Yes. OTR uses the socialist millionaires protocol, which is an interactive protocol Alice and Bob use to establish confidence that their secrets match (without either of them disclosing the secret). If the authentication succeeded, both parties store the public key fingerprint of the other and mark it as trusted. The shared secret is not used any further (e....


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