an't use Jill's public key to decrypt files intended for Jill (since decrypting a file intended for Jill requires Jill's private key), nor can he sign files pretending to be Jill. Even if Jack got his hands on Jill's private key file, he would need Jill's password to access it.
The biggest problem with this method of encryption is verifying that the sender is who he or she claims to be. The solution is called a "Web of Trust", which makes use of digital signatures. If Jill wants to verify that the Jack who sent her an encrypted file is really the Jack she knows, she confirms his identity by some non-electronic method, such as a personal meeting or phone call, or by an electronic method such as the AT&T Pathserver. If Jack has previously taken similar steps to confirm the identity of John Doe, Jill can also trust an encrypted file from John.
See an illustrated model of encrypting and signing data. These pages are part of the Asia Pacific Network Information Centre's Certificate Authority Status Report.
Some software programs are more useful for encrypting files, and others are more useful for encrypting text messages, like email and instant messages. It's possible to use a file-encryption program for both files and email. Some file-encryption programs, for example, encrypt email by transforming the message into a file, and then sending the encrypted file. However, some of the software specifically designed for email encryption is much easier to use than programs for file encryption. Other email encryption software programs convert plaintext to ciphertext, which is useful for encrypting email or text documents, but useless for encrypting images or other non-text files. Other encryption software simply enables you to store encrypted files on your computer.
In addition to the different encryption algorithms and models, there are different software interfaces. Some programs require you to locate the file you want to encrypt through a regular "file-open" dialogue window. Others, including PGP, allow you to encrypt a highlighted section of text that you select from an open document. Some email encryption programs include plug-ins that add buttons to your program menu, so you can encrypt a message with literally the touch of a button. These interface alternatives can be important for first-time users since they can make the software easier to use. They are also important for anyone who uses encryption daily, since a cumbersome encryption and decryption process may deter use.
When you try an encryption program, check for the features that you need (e.g. encrypts your email, encrypts your files, etc.), as well as its ease of use.
Some features you may find useful in any encryption software:
Some features you may find useful in email encryption software:
Some features you may find useful in file encryption software:
You should also become familiar with any encryption features that may have been built into your computer's operating system. If your computer's operating system includes features that provide the level of security you need, it may not be necessary to look for those features in third-party encryption software programs.
Features offered by:
Mac OS 9 includes some built-in encryption features that are relatively easy to use: Apple File Security and Apple Verifier. Located in the Security Folder (which is in the Applications Folder), these features allow Mac users to encrypt and decrypt files on their hard drives, and to verify the authenticity of files containing digital signatures. To encrypt or decrypt files, drag them onto the Apple File Security icon. To verify digital signatures, drag them onto the Apple Verifier icon. The Apple Help menu includes information on how to use these features.
The Unix security system is robust and complex. It employs a system of access control lists to determine which users have access to a given file or folder, and usually requires that users log-on to use the computer. (Keep in mind that access controls are not the same as encryption.) To learn more, check the following link: http://www