JavaScrypt runs entirely in your browser--nothing is sent to any Web site when you use it. You can, if you wish, download JavaScrypt to your own computer and use it when not connected to the Internet.
JavaScrypt's encryption facilities use the Advanced Encryption Standard (AES) adopted by the United States as Federal Information Processing Standard 197. AES supports key lengths of 128, 192, and 256 bits; JavaScrypt uses 256 bit keys exclusively.
If you're already familiar with encryption, proceed directly to the pages which implement the various components of JavaScrypt. If you're a newcomer, you may prefer to work through the JavaScrypt Tutorial, which demonstrates how they're used.
Security. The sole reason for encryption is to protect privacy. This means the process cannot involve any link whose security is suspect. If messages were encrypted by a Web server, they would have to pass over the Internet, where any intermediate site might intercept them. Even if some mechanism such as secure HTTP could absolutely prevent the data's being intercepted, you'd still have no way to be sure the site which performed the encryption didn't keep a copy in a file, conveniently tagged with your Internet address.
Security is never absolute. Data encrypted with these pages might be compromised in a variety of ways, including but not limited to the following:
Transparency. Any security-related tool is only as good as its design and implementation. Transparency means that, in essence, all the moving parts are visible so you can judge for yourself whether the tool merits your confidence. In the case of a program, this means that complete source code must be available, and that you can verify that the program you're running corresponds to the source code provided.
Transparency is important even if you don't know enough about programming or security to determine whether the programs contain any flaws. The very fact that they can be examined by anybody allows those with the required expertise to pass judgment, and you can form your own conclusions based on their analysis.