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docs/glossary.html

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 <p>Nodes in the overlay network can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. Tor, for example, is an overlay network on top of IP network, which in its turn is also an overlay network over some underlying physical network.</p>
 <p>SimpleX Clients also form a network using SMP relays and IP or some other overlay network (e.g., Tor), to communicate with each other. SMP relays, on another hand, do not form a network.</p>
 <p><a href="https://en.wikipedia.org/wiki/Overlay_network">Wikipedia</a></p>
+<h1 id="non-repudiation" tabindex="-1">Non-repudiation</h1>
+<p>The property of the cryptographic or communication system that allows the recipient of the message to prove to any third party that the sender identified by some cryptographic key sent the message. It is the opposite to <a href="#repudiation">repudiation</a>. While in some context non-repudiation may be desirable (e.g., for contractually binding messages), in the context of private communications it may be undesirable.</p>
+<p><a href="https://en.wikipedia.org/wiki/Non-repudiation">Wikipedia</a></p>
 <h2 id="pairwise-pseudonymous-identifier" tabindex="-1">Pairwise pseudonymous identifier</h2>
 <p>Generalizing <a href="https://csrc.nist.gov/glossary/term/pairwise_pseudonymous_identifier">the definition</a> from NIST Digital Identity Guidelines, it is an opaque unguessable identifier generated by a service used to access a resource by only one party.</p>
 <p>In the context of SimpleX network, these are the identifiers generated by SMP relays to access anonymous messaging queues, with a separate identifier (and access credential) for each accessing party: recipient, sender and and optional notifications subscriber. The same approach is used by XFTP relays to access file chunks, with separate identifiers (and access credentials) for sender and each recipient.</p>
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 <p>Network topology of the communication system when peers communicate via proxies that do not form the network themselves. Such design is used in Pond, that has a fixed home server for each user, and in SimpleX, that uses multiple relays providing temporary connections.</p>
 <h2 id="recovery-from-compromise" tabindex="-1">Recovery from compromise</h2>
 <p><a href="#post-compromise-security">Post-compromise security</a>.</p>
+<h2 id="repudiation" tabindex="-1">Repudiation</h2>
+<p>The property of the cryptographic or communication system that allows the sender of the message to plausibly deny having sent the message, because while the recipient can verify that the message was sent by the sender, they cannot prove it to any third party - the recipient has a technical ability to forge the same encrypted message. This is an important quality of private communications, as it allows to have the conversation that can later be denied, similarly to having a private face-to-face conversation.</p>
+<p>See also <a href="#non-repudiation">non-repudiation</a>.</p>
 <h2 id="user-identity" tabindex="-1">User identity</h2>
 <p>In a communication system it refers to anything that uniquely identifies the users to the network. Depending on the communication network, it can be a phone number, email address, username, public key or a random opaque identifier. Most messaging networks rely on some form of user identity. SimpleX appears to be the only messaging network that does not rely on any kind of user identity - see <a href="https://en.wikipedia.org/wiki/Comparison_of_instant_messaging_protocols">this comparison</a>.</p>
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