1. Contrast: Encoding is not encryption. A lot of passwords are sent across the wire encoded (such as HTTP's BASE64 encoded passwords). In essence, they are still clear-text passwords; most password sniffers will still read them from the wire. Example: The main issue with encoding is how to get binary data sent within a text message. For full binary data, this results in about 40% "expansion" of the file size (i.e. when you e-mail 1-megabyte of data to a fried, this encoding will result in about a 1.4-megabyte message size). BASE64 aka. RADIX64. Content-Transfer-Encoding: Base64 The preferred encoding method these days for MIME e-mail messages and virtually everywhere else. uuencode and uudecode UNIX-to-UNIX While having been largely replaced with BASE64 encoding, uuencoding is the granddady of encoding methods. It increases the file size roughly 42%. It was originally developed for e-mail encoding. Few e-mail programs generate this encoding, but most all of them can decode it. The main reason for its disfavor is that a lot of programs are slightly inconsistent in the way that they encode/decode data using this technique, subtly corrupting files. See also: uucp. quoted printable Content-Transfer-Encoding: quoted-printable This consists of normal ASCII text, where any binary character (or other problematic character such as a space at the end of the line) is converted to a 3-character code consisting of the equals sign followed by two hex digits representing the binary value. For example, the code =20 indicates a single character with the hex value of 0x20, which is equal to decimal 32. In ASCII, this is a space. E-mail messages are often automatically line-wrapped for long lines. The line is frequently wrapped after a space between two words, resulting in a space at the end of a line. Therefore, you will sometimes see e-mail messages with a lot of lines ending in =20 due to the requirements of this encoding method to encoding trailing spaces. This encoding is most often used for European text (especially French) which has occasional accented characters in what is otherwise largely ASCII text. BinHex. A standard Macintosh encoding method; rarely used elsewhere. Key point: E-mail clients typical support more encoding methods than content scanners (aka. anti-virus scanners). Therefore, by encoding your e-mail correctly, you can often bypass these. Key point: A big problem in the security industry is the presences of redunant encoding methods Microsoft's web servers were hacked because of redundant ways of encoding UNICODE characters. TODO See also: UNICODE From Hacking-Lexicon