Definition of uuencoding in The Network Encyclopedia.

What is Uuencoding?

Uuencoding is a method of encoding binary files into 7-bit ASCII text that was originally developed for UNIX platforms. Uuencoding enables you to attach binary files to e-mail messages and transmit them over the Internet using Simple Mail Transfer Protocol (SMTP). The sending program first “uuencodes” the attachments and sends them with the e-mail message, which the receiving program “uudecodes” into its original binary format.

Although still popular on some platforms, uuencoding has been largely superseded by Multipurpose Internet Mail Extensions (MIME), a more sophisticated scheme for encoding multipart e-mail messages. Uuencoding is still used in one context in Microsoft Windows, namely for Basic Authentication on Internet Information Services (IIS). Basic Authentication transmits the user’s credentials between the Web browser client and the IIS computer in uuencoded form. This method is commonly referred to as clear-text transmission, although if you were to capture authentication traffic by using a network sniffer such as Microsoft Network Monitor, you would be unable to read the user’s credentials without uudecoding the information. Uuencoding is not considered a cryptographic algorithm because it is extremely simple to crack.


An encoding method similar to uuencoding that is implemented on Apple Macintosh systems is called BinHex.


You can tell that a binary file has been uuencoded into an ASCII text file if the text of the file starts with «begin 644…».