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Digital Signature
A digital signature is an electronic equivalent of an individual's signature. It authenticates the message to which it is attached and validates the authenticity of the sender. In addition, it also provides confirmation that the contents of the message to which it is attached, have not been tampered with, en route from the sender to the receiver.
A further feature is that an e-mail 'signed' with a digital signature cannot easily be repudiated; i.e. the sender is not able to deny the sending and the contents of the message; plus it provides a digital time stamp to confirm the time and date of transmission.
For a digital signature to be recognised, and acknowledged as something of integrity, it needs to be trusted by the recipient. It is for this reason that a Certification Authority will supply a digital signature to persons, the identity of whom, it has been able to verify; perhaps by having an Attorney's stamp on a document which validates the applicant's name, address, date of birth etc.
To provide greater digital trust, the Digital Signature is packaged with the certificate of the Certification Authority, and this too may be inspected for validity and expiration.
Most people expect digital signatures to totally replace the use of the ('old fashioned') pen and ink signature with orders and authorities being accepted via digitally signed e-mails, the contents of which may, or may not, be encrypted for additional security.
N.B. In July 2000, Digital Signatures became legally accepted in the United Kingdom under Section 7 of the Electronic Communications Act. In the USA also, Congress approved the use of Digital Signatures for certain types of e-Business around the same time under the E-Sign Act. Because both Acts are extremely new, it is strongly recommended that legal advice be sought before reliance is placed upon this new legislation.
digital signature
A digital signature uses encryption
technology to do two things. It proves that the message hasn’t been
changed in transit, called message integrity, and it also links
ownership to the information, called non-repudiation.
In order to prove that the message wasn’t changed the message is
cryptographically transformed to a set of values, called a hash or a
digest. The hash or digest is also sometimes referred to as a
fingerprint because statistically, the chance of this hash or digest
being the same value for any other message is almost impossible. The
hash or digest is sent along with the message and the same
transformation is run at the other end. Any attempts to alter the
information in transit will result in a message that no longer matches
its digital signature.
In order to link ownership, before the message is sent, a second
operation is performed. The private key of the sender is used to
encrypt the hash or digest. The receiver uses the sender’s public key
to decrypt the digest. This proves that the message could only come
from the person who holds the private key.
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