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  Computers
 
Simple PHP mail script

This script is not only educational, but also applicable for practical web development. It allows you to place a simple form for sending emails on any HTML page. The script shows you how to gather user input, perform form validation with PHP, and send an email. As you see, the script is simply one if ... elseif ... else statement. At first, it validates the required form fields. Note that PHP form validation is performed on the server, after sending all the data. Therefore, it would be a good idea to combine server-side form validation with PHP and client-side form...

PHP Include File

You can insert the content of a file into a PHP file before the server executes it, with the include() or require() function. The two functions are identical in every way, except how they handle errors. The include() function generates a warning (but the script will continue execution) while the require() function generates a fatal error (and the script execution will stop after the error). These two functions are used to create functions, headers, footers, or elements that can be reused on multiple pages. This can save the developer a considerable amount of time. This means that you can create...

Multiple Page Forms

So you have this long, involved form. Rather than present the user with a myriad of inputs on a single page, you want to break this up into separate form pages. So now you're asking, "How do you make multiple page forms?" I'm glad you asked. It's easy!What's that bit of code do? If you were to place the above code between your opening form tag and the closing form tag, it will look at all values received from the prior page, strips out any HTML tags, replaces any character entities with their appropriate code and writes them to hidden...

Cryptography

CRYPTOGRAPHY (from Gr. Kpinrros, hidden, and ypiL4aI, to write), or writing in cipher, called also steganography (from Gr. crreyvij, a covering), the art of writing in such a way as to be incomprehensible except to those who possess the key to the system employed. The unravelling of the writing is called deciphering. Cryptography having become a distinct art, Bacon (Lord Verulam) classed it (under the name ciphers) as a part of grammar. Secret modes of communication have been in use from the earliest times. The Lacedemonians had a method called the scytale, from the staff (o~KvrfiXfl) employed in constructing and...

A Brief History of Cryptography - compiled by Shireen Hebert

Cryptography, the science of encrypting and decrypting information, dates as far back as 1900 BC when a scribe in Egypt first used a derivation of the standard hieroglyphics of the day to communicate. Carl Ellison, Cryptography Timeline. There are many notable personalities who participated in the evolution of Cryptography. For example, “Julius Caesar (100-44 BC) used a simple substitution with the normal alphabet (just shifting the letters a fixed amount) in government communications”, and later, Sir Francis Bacon in 1623, who "described a cipher which now bears his name -- a biliteral cipher, known today as a 5-bit binary...

Cryptography: History

When one thinks of cryptography, one imagines spies and espionage, yet the art and practice of cryptography is going on about us everyday of our lives. Its art and practice is part of the fabric of society and we have all practiced this science in one way or another. In practice, cryptography is the science of transmitting information from one location to another, with the added requirement that this message cannot be understood by someone other than the sender and the receiver. Most people would accept this as the standard definition of this science. Yet, as you have read this,...

Introduction to Cryptosystems

Cryptology is the hiding of information so that it is unintelligable to those we do not wish to read it and intelligable to those we do. In this section we present the fundamental or basic ideas needed to understand the science. We start with the question, what information are we trying to hide? The answer can range from any number of things; however most importantly it is information that we want to keep private. For instance, bank account numbers and social security numbers are pieces of information that we don't want everyone to be able to obtain. For military purposes,...

Cryptanalysis and Attacks on Cryptosystems

Ciphertext-only attack: This is the situation where the attacker does not know anything about the contents of the message, and must work from ciphertext only. In practice it is quite often possible to make guesses about the plaintext, as many types of messages have fixed format headers. Even ordinary letters and documents begin in a very predictable way. For example, many classical attacks use frequency analysis of the ciphertext, however, this does not work well against modern ciphers. There are many other cryptographic attacks and cryptanalysis techniques. However, these are probably the most important ones for an application designer. Anyone...

Strength of Cryptographic Algorithms

Good cryptographic systems should always be designed so that they are as difficult to break as possible. It is possible to build systems that cannot be broken in practice (though this cannot usually be proved). This does not significantly increase system implementation effort; however, some care and expertise is required. There is no excuse for a system designer to leave the system breakable. Any mechanisms that can be used to circumvent security must be made explicit, documented, and brought into the attention of the end users. Unpublished or secret algorithms should generally be regarded with suspicion. Quite often the designer...

Cryptographic Random Number Generators

Cryptographic random number generators generate random numbers for use in cryptographic applications, such as for keys. Conventional random number generators available in most programming languages or programming environments are not suitable for use in cryptographic applications (they are designed for statistical randomness, not to resist prediction by cryptanalysts). In the optimal case, random numbers are based on true physical sources of randomness that cannot be predicted. Such sources may include the noise from a semiconductor device, the least significant bits of an audio input, or the intervals between device interrupts or user keystrokes. The noise obtained from a physical source...

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