Digital Signatures are not a Scanned Handwritten Signatures

Digital Signatures are not a Scanned Handwritten Signatures

Digital Signatures

A digital signature is an electronic signature that can be used to authenticate the identity of the sender of a message or the signer of a document, and to ensure that the original content of the message or document that has been sent is unchanged. Digital signatures are easily transportable, cannot be imitated by someone else, and can be automatically time-stamped. A digital signature can be used with any kind of message, whether it is encrypted or plaintext. Thus Digital Signatures provide the following three features:-

Authentication- Digital signatures are used to authenticate the source of messages. The ownership of a digital signature key is bound to a specific user and thus a valid signature shows that the message was sent by that user.

Integrity - In many scenarios, the sender and receiver of a message need assurance that the message has not been altered during transmission. Digital Signatures provide this feature by using cryptographic message digest functions (discussed in detail in section 4.4).

Non Repudiation – Digital signatures ensure that the sender who has signed the information cannot at a later time deny having signed it.

4.2 Digital Signature Versus Handwritten Signatures

A handwritten signature scanned and digitally attached with a document does not qualify as a Digital Signature.

A Digital Signature is a combination of 0 & 1s created using crypto algorithms.

An ink signature can be easily replicated from one document to another by copying the image manually or  electronically. Digital Signatures cryptographically bind an electronic identity to an electronic document and the digital signature cannot be copied to another document. Further, paper contracts often have the ink signature block on the last page, allowing previous pages to be replaced after the contract has been signed. Digital signatures on the other hand compute the hash or digest of the complete document and a change of even one bit in the previous pages of the document will make the digital signature verification fail. As can be seen in the underlying figure, a Digital Signature is a string of bits appended to a document. The size of a digital signature depends on the Hash function like SHA 1 / SHA2 etc used to create the message digest and the signing key. It is usually a few bytes. 

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