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Digital Signatures

We are all familiar with paper signatures - a hand-written signature on a paper document. Aside from legal and contractual issues, the primary properties of a paper signature are:

it is intended to be associated with a particular individual;
it generally shows a commitment related to a particular document, with the exact meaning depending on context.

Though far from perfect, paper signatures serve surprisingly well in many parts of the world as the basis for business and legal transactions. Societies have learned to use paper signatures in circumstances in which a physical marking on a paper document, augmented by sufficient controls and context, provides sufficient recallable evidence of a commitment related to that document by the marking party. The evidence is important in order to reconstruct circumstances, in the rare case of later disputes.

A digital signature is the term used for marking or signing an electronic document, by a process meant to be analogous to paper signatures, but which makes use of a technology known as public-key cryptography. Additional security properties are required of signatures in the electronic world. This is because the probability of disputes rises dramatically for electronic transactions without face-to-face meetings, and in the presence of potentially undetectable modifications to electronic documents. Digital signatures address both of these concerns, and offer far more inherent security than paper signatures. Compared to all other forms of signatures, digital signatures are by far the most easily verified and the most reliable with respect to providing document integrity.

Property	Paper Signatures	Digital Signatures
Can be applied to electronic documents and transactions	No	Yes
Signature verification can be automated	No	Yes
Signature automatically detects alterations to the document	No	Yes
Can be used to signify a commitment to a contract or document	Yes	Yes
Can be augmented by use of a witness to the signature process	Yes	Yes
Recognized by legislation	Yes	Yes

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