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Speaker 1: Welcome to Brainstuff from house stuff works dot com where

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Speaker 1: smart happens. Hi, I'm our so brain with today's question,

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Speaker 1: what is a digital signature? A digital signature is basically

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Speaker 1: a way to ensure that an electronic document, like an

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Speaker 1: email message, or a spreadsheet or a text file, is authentic.

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Speaker 1: Authentic means that you know who created the document, and

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Speaker 1: you know that it has not been altered in any

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Speaker 1: way since that person created it. Digital signatures rely on

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Speaker 1: certain types of encryption to ensure that authentication. Encryption is

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Speaker 1: the process of taking all the data that one computer

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Speaker 1: is sending to another computer and encoding it into a

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Speaker 1: form that only the receiving computer will be able to decode.

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Speaker 1: Authentication is the process of verifying that unaltered information is

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Speaker 1: coming from a trusted source. These two processes were cand

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Speaker 1: in hand for digital signatures. There are several ways to

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Speaker 1: authenticate a person or information on a computer. The most

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Speaker 1: common way is to use some kind of password scheme.

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Speaker 1: The use of a user name and password provide the

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Speaker 1: most common form of authentication. You enter your name and

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Speaker 1: password when prompted by the computer. It checks the pair

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Speaker 1: against the secure file to confirm. If either the name

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Speaker 1: or the password don't match, then you're not allowed further

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Speaker 1: access to the document. Many text editors, like Microsoft Word

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Speaker 1: offer this feature. You simply encode the document before you

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Speaker 1: send it, put the password on it, and then the

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Speaker 1: recipient who you tell the password to, the only one

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Speaker 1: who can read that document. The second idea is a checksum.

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Speaker 1: It's probably one of the oldest methods of ensuring that

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Speaker 1: data is correct, and checksums also provide a form of authentication,

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Speaker 1: since an invalid checksums suggests that the data has been

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Speaker 1: compromised in some fashion while it was being sent. A

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Speaker 1: checksum is determined in one of two ways. Let's say

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Speaker 1: that the checksum of a packet is one bite long,

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Speaker 1: which means it can have a maximum value of two

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Speaker 1: fifty five. If the sum of all the bites in

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Speaker 1: the packet is two fifty five or less, then the

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Speaker 1: checksum contains that exact value. However, if the sum of

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Speaker 1: the other bites is more than two D fifty five,

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Speaker 1: then the checksum is the remainder of the total value

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Speaker 1: after it's been divided by two D fifty six. Another

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Speaker 1: technique called a CRC or cyclic redundancy check, is similar

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Speaker 1: in concept to checksums. Neither checksums or CRCs really provide

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Speaker 1: any protection of the data. They just tell you that

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Speaker 1: it hasn't been tampered with as it made its way

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Speaker 1: to your computer. Then there's private key encryption. Private key

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Speaker 1: means that each computer as a secret key or secret

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Speaker 1: code that it can use to encrypt a packet of

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Speaker 1: information before it's sent over the network to the other computer.

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Speaker 1: Private key requires that you know which computers will talk

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Speaker 1: to each other and install the key on each one

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Speaker 1: ahead of time. Private key encryption is essentially the same

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Speaker 1: as a secret code that the two computers must each

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Speaker 1: know in order to decode the information when it arrives.

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Speaker 1: The code would provide the key to decoding the message.

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Speaker 1: Your friend gets the message and then decodes it. Anyone

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Speaker 1: else who sees the message will see only nonsense because

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Speaker 1: they don't have the key. Then there's public key encryption.

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Speaker 1: Public key encryption uses a combination of a private key

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Speaker 1: and a public key. The private key is known only

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Speaker 1: to your computer, while the public key is given by

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Speaker 1: your computer to any computer that wants to communicate with it.

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Speaker 1: To decode an encrypted message, a computer must use the

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Speaker 1: public key provided by the originating computer and its own

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Speaker 1: private key, and then there are digital certificates. To implement

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Speaker 1: public key encryption on a large scale, such as a

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Speaker 1: secure web server might need, requires a different approach. This

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Speaker 1: is where digital certificates come in. A digital certificate is

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Speaker 1: essentially a bit of information that says the web server

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Speaker 1: is trusted by an independent source known as a certificate authority.

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Speaker 1: The certificate authority acts as a middleman that both computers trust.

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Speaker 1: It confirms that each computer is in fact who they

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Speaker 1: say they are, and then provides the public keys of

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Speaker 1: each computer to the other. The Digital Signature Standard is

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Speaker 1: based on a type of public key encryption that uses

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Speaker 1: the digital signature out gorhythm. The Digital Signature Standard is

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Speaker 1: the format for digital signals that's been endorsed by the

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Speaker 1: US government. For more on this and thousands of other topics,

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Speaker 1: visit how Stuff Works dot com, and don't forget to

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Speaker 1: check out the brain Stuff blog on the house stuff

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Speaker 1: works dot com home page. You can also follow brain

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Speaker 1: stuff on Facebook or Twitter at brain stuff hs W.

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