Month: January 2010

What is a digital signature?

A digital signature is basically a way to ensure that an electronic document (e-mail, spreadsheet, text file, etc.) is authentic. Authentic means that you know who created the document and you know that it has not been altered in any way since that person created it.

Digital signatures rely on certain types of encryption to ensure authentication. Encryption is the process of taking all the data that one computer is sending to another and encoding it into a form that only the other computer will be able to decode. Authentication is the process of verifying that information is coming from a trusted source. These two processes work hand in hand for digital signatures.

There are several ways to authenticate a person or information on a computer:

  • Password – The use of a user name and password provide the most common form of authentication. You enter your name and password when prompted by the computer. It checks the pair against a secure file to confirm. If either the name or password do not match, then you are not allowed further access.
  • Checksum – Probably one of the oldest methods of ensuring that data is correct, checksums also provide a form of authentication since an invalid checksum suggests that the data has been compromised in some fashion. A checksum is determined in one of two ways. Let’s say the checksum of a packet is 1 byte long, which means it can have a maximum value of 255. If the sum of the other bytes in the packet is 255 or less, then the checksum contains that exact value. However, if the sum of the other bytes is more than 255, then the checksum is the remainder of the total value after it has been divided by 256. Look at this example:
    Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 Byte 8 Total Checksum
    212 232 54 135 244 15 179 80 1151 127

    1151 divided by 256 equals 4.496 (round to 4)
    Multiply 4 X 256 which equals 1024
    1151 minus 1024 equals 127

  • CRC (Cyclic Redundancy Check) – CRCs are similar in concept to checksums but they use polynomial division to determine the value of the CRC, which is usually 16 or 32 bits in length. The good thing about CRC is that it is very accurate. If a single bit is incorrect, the CRC value will not match up. Both checksum and CRC are good for preventing random errors in transmission, but provide little protection from an intentional attack on your data. The encryption techniques below are much more secure. 
  • Private key encryption -Private key means that each computer has a secret key (code) that it can use to encrypt a packet of information before it is sent over the network to the other computer. Private key requires that you know which computers will talk to each other and install the key on each one. Private key encryption is essentially the same as a secret code that the two computers must each know in order to decode the information. The code would provide the key to decoding the message. Think of it like this. You create a coded message to send to a friend where each letter is substituted by the letter that is second from it. So “A” becomes “C” and “B” becomes “D”. You have already told a trusted friend that the code is “Shift by 2”. Your friend gets the message and decodes it. Anyone else who sees the message will only see nonsense. 
  • Public key encryption – Public key encryption uses a combination of a private key and a public key. The private key is known only to your computer while the public key is given by your computer to any computer that wants to communicate securely with it. To decode an encrypted message, a computer must use the public key provided by the originating computer and it’s own private key.The key is based on a hash value. This is a value that is computed from a base input number using a hashing algorithm. The important thing about a hash value is that it is nearly impossible to derive the original input number without knowing the data used to create the hash value. Here’s a simple example:
    Input number Hashing algorithm Hash value
    10667 Input # x 143 1525381

    You can see how hard it would be to determine that the value of 1525381 came from the multiplication of 10667 and 143. But if you knew that the multiplier was 143, then it would be very easy to calculate the value of 10667. Public key encryption is much more complex than this example but that is the basic idea. Public keys generally use complex algorithms and very large hash values for encrypting: 40-bit or even 128-bit numbers. A 128-bit number has a possible 2128 different combinations. That’s as many combinations as there are water molecules in 2.7 million olympic size swimming pools. Even the tiniest water droplet you can image has billions and billions of water molecules in it!

  • Digital certificates – To implement public key encryption on a large scale, such as a secure Web server might need, requires a different approach. This is where digital certificates come in. A digital certificate is essentially a bit of information that says the Web server is trusted by an independent source known as a Certificate Authority. The Certificate Authority acts as the middleman that both computers trust. It confirms that each computer is in fact who they say they are and then provides the public keys of each computer to the other.

The Digital Signature Standard (DSS) is based on a type of public key encryption method that uses the Digital Signature Algorithm (DSA). DSS is the format for digital signatures that has been endorsed by the US government. The DSA algorithm consists of a private key that only the originator of the document (signer) knows and a public key.

How Blogs Work.

Blogs appear on the news pretty often these days. For example, a reporter is tipped to a story by a blog, or a blog reports another angle on a story. Blogs show up in magazines a lot, too.

But there is a good chance you have never seen a blog (also known as a weblog) or experienced the blogosphere. What are blogs? There are now millions of them — where did they all come from?

One of the things that is so amazing about blogs is their simplicity.

Think about a “normal Web site.” It usually has a home page, with links to lots of sub-pages that have more detail. HowStuffWorks is like this, with thousands of information pages all organized under a home page. A small business site follows the same format — it might have a home pag­e and five or 10 sub-pages. Most traditional Web sites follow this format. If the site is small, it is sort of like an online brochure. If it is large, it is like an electronic encyclopedia.

­ A typical Web site has a home page that links to sub-pages within the site. is typical of this genre. The CNN site contains thousands of articles all organized into big categories. The categories and all the latest stories are accessed from the home page.

A blog is much simpler:

  • A blog is normally a single page of entries. There may be archives of older entries, but the “main page” of a blog is all anyone really cares about. 
  • A blog is organized in reverse-chronological order, from most recent entry to least recent. 
  • A blog is normally public — the whole world can see it. 
  • The entries in a blog usually come from a single author
  • The entries in a blog are usually stream-of-consciousness. There is no particular order to them. For example, if I see a good link, I can throw it in my blog. The tools that most bloggers use make it incredibly easy to add entries to a blog any time they feel like it.


­­In this article, you will have a chance to enter the world of blogging. You will even learn how to create your own blog and publish it to the world.

Blogging Basics

A typical blog has a main page and nothing else. On the main page, there is a set of entries. Each entry is a little text blurb that may contain embedded links out to other sites, news stories, etc. When the author adds a new entry, it goes at the top, pushing all the older entries down. This blog also has a right sidebar that contains additional permanent links to other sites and stories. The author might update the sidebar weekly or monthly.

sample blog

Basically, a blog is a lot like an online journal or diary. The author can talk about anything and everything. Many blogs are full of interesting links that the author has found. Blogs often contain stories or little snippets of information that are interesting to the author.

Even though blogs can be completely free-form, many blogs have a focus. For example, if a blogger is interested in technology, the blogger might go to the Consumer Electronics Show and post entries of the things he/she sees there. If a blogger is interested in a certain disease, he/she might post every news article and every piece of research he/she finds on the disease. If a blogger is interested in economic issues, he/she might post links to articles that discuss the economy and then offer commentary on them.

There are people who use their blogs simply as a scrapbook — a form of online memory. Whenever the author finds a link or a snippet of information that he/she wants to remember, it gets posted in the blog. Even if no one else ever looks at it, it is still useful to the author because the blog is a searchable electronic medium that the author can access with a Web browser anywhere in the world.

In other words, a blog can be anything the author wants it to be. The thing that all blogs have in common is the reverse-chronological ordering of entries.