Digital Signature Usability

1. Digital Signature Usability Ravi Sandhu George Mason University and TriCipher

2. Objectives • Emphasize usability not cryptography • But they are interrelated • All the same there are some purely usability issues on which we currently do a terrible job

3. Think outside the box • Cryptography alone cannot provide assurance of signatures. • It is necessary but not even close to being sufficient • Also need elements of “trusted computing” • founded on a strong hardware base for high assurance • The needs of transaction signatures are very different from those of document or email signatures • Transaction signatures rather than signed email may be the killer application • The biggest productivity gains are in volume of low-grade transactions not so much in automating really high end transactions • There is no such thing as an offline transaction • Transactions are typically verified by computers not by people

4. Questions (signer oriented) • Can users execute the signature procedure when appropriate? • Do they understand when it's appropriate? • Do they realize the consequences of their actions? • Can they recover if they accidentally make a mistake? • What clues are provided to guide them? • Do all signatures need to be of the same strength? • Who determines what the strength of a signature should be?

5. Questions (verifier oriented) • Is the verifier a human or a computer • Signed email: human verifier • Signed transaction: computer verifier with possibly human audit and recourse forensics • How do we deal with the revocation problem? • Should the verifier even be responsible for this problem? • Do I have responsibility for ensuring that the signer signed what I intended for the signer to sign? • Is there a notion of a verification chain?

6. PEI Models Framework