# Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob.

Bob stores the decrypted message and the digital signature in a database.

However Alice is a bad girl and erases all data from her side, including her private/public keys. She then claims she never sent the message.

Is there a solution to this case?

In my case, Alice uses a communication tool that Bob has provided, where the private/public key are generated within the context of the tool (with no 'public key' advertised somewhere else, hence making it even more difficult to prove anything)

• Who's the dishonest third party? Alice isn't a third party; she's a normal party to the communication, whereas a third party is someone who's not supposed to be directly involved with the communication. – cpast Feb 1 '15 at 17:13
• correct - I have changed the title – user3684457 Feb 1 '15 at 17:41

• Yes. $\:$ That issue is also fundamental for nonrepudiation, but it's independent $\hspace{1.75 in}$ of the issue raised in your opening post. $\;\;\;\;$ – user991 Feb 1 '15 at 22:34
• The most generic way is a (physically) signed contract stating that, in return for something, Alice will be bound to a certain extent by signed messages that are compatible with [specific public key]. $\:$ One potential alternative is a (video-and-audio) recording of Alice stating that she will be bound to a certain extent by signed messages that are compatible with [specific public key]. $\;\;\;\;$ – user991 Feb 1 '15 at 22:59