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A digital
signature (not to be confused with a digital
certificate) is a mathematical technique used to validate the
authenticity and integrity of a message, software or digital document.
The digital
equivalent of a handwritten signature or stamped seal, but offering far more
inherent security, a digital signature is intended to solve the problem of
tampering and impersonation in digital communications. Digital signatures can
provide the added assurances of evidence to origin, identity and status of an
electronic document, transaction or message, as well as acknowledging informed
consent by the signer.
In many
countries, including the United States, digital signatures have the same legal
significance as the more traditional forms of signed documents. The United
States Government Printing Office publishes electronic versions of the budget,
public and private laws, and congressional bills with digital signatures.
How digital signatures work
Digital
signatures are based on public key cryptography, also known as asymmetric
cryptography. Using a public key
algorithm
such as RSA,
one can generate two keys that are mathematically linked: one private and one
public. To create a digital signature, signing software (such as an
email program) creates a one-way hash of the electronic data to be signed. The private key
is then used to encrypt the hash. The encrypted hash -- along with other
information, such as the hashing
algorithm -- is the digital signature. The reason for encrypting the hash
instead of the entire message or document is that a hash function can convert
an arbitrary input into a fixed length value, which is usually much shorter.
This saves time since hashing is much faster than signing.
The value of
the hash is unique to the hashed data. Any change in the data, even changing or
deleting a single character, results in a different value. This attribute
enables others to validate the integrity of the data by using the signer's
public key to decrypt the hash. If the decrypted hash matches a second computed
hash of the same data, it proves that the data hasn't changed since it was
signed. If the two hashes don't match, the data has either been tampered with
in some way (integrity) or the signature was created with a private key that
doesn't correspond to the public key presented by the signer (authentication).
A digital signature can be used with any kind of message
-- whether it is encrypted or not -- simply so the receiver can be sure of the
sender's identity and that the message arrived intact. Digital signatures make
it difficult for the signer to deny having signed something (non-repudiation)
-- assuming their private key has not been compromised -- as the digital
signature is unique to both the document and the signer, and it binds them
together. A digital certificate, an electronic document that contains the
digital signature of the certificate-issuing authority, binds together a public
key with an identity and can be used to verify a public key belongs to a
particular person or entity.
If the two hash values match, the message has not been
tampered with, and the receiver knows the message is from sender.
Most modern email programs support the use of digital signatures
and digital certificates, making it easy to sign any outgoing emails and
validate digitally signed incoming messages. Digital signatures are also used
extensively to provide proof of authenticity, data integrity and
non-repudiation of communications and transactions conducted over the Internet.
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In addition to this blog, Netiquette IQ has a website with great assets which are being added to on a regular basis. I have authored the premiere book on Netiquette, “Netiquette IQ - A Comprehensive Guide to Improve, Enhance and Add Power to Your Email". My new book, “You’re Hired! Super Charge Your Email Skills in 60 Minutes. . . And Get That Job!” will be published soon follow by a trilogy of books on Netiquette for young people. You can view my profile, reviews of the book and content excerpts at:
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