yEnc is an encoding for transferring binary files on the Usenet or via e-mail. It reduces the overhead by using an 8-bit transfer method. The overhead can be as little as 1-2% compared to the 33%-40% of other encodings like uuencode and Base64, although this is at the expense of transport reliability.

There is no RFC or other standards document describing yEnc. The yEnc homepage contains a draft informal specification and a grammar (which contradicts RFC 2822 and RFC 2045), although neither have been submitted to the Internet Engineering Task Force.

The creator of the yEnc encoding scheme, Jeremy Nixon, and others have criticized the design of yEnc. It suffers from many of the same flaws (most notably that encoded entities cannot be reliably detected) as uuencode does, a number of which had already been solved years before by MIME (which itself addressed the same flaws in uuencode). Moreover, yEnc adds a few new flaws of its own. It attempts to turn unstructured fields into structured ones, which is unreliable given that no constraints can be placed upon the unstructured use of the fields by non-yEnc uses. (The yEnc homepage chastises yEnc article posters for themselves not observing these constraints.) Not all article transports can handle the 8-bit characters employed by yEnc, which may cause data corruption. Moreover, some article transports may, on the grounds of enforcing compliance with the Internet message format standard, automatically convert any messages using 8-bit characters to either Base64 or Quoted-printable, entirely nullifying the compression overhead advantage.

However, as with uuencoding, despite its flaws yEnc remains in use on Usenet. As with uuencode, there are specialised programs for encoding files to, and decoding them from, multiple Usenet postings. The yEnc homepage states that "all major newsreaders have been extended to yEnc support". Neither Outlook Express nor Mozilla provide yEnc support, for either news or mail.

See also

• Radix-64
• ASCII Armor

External links

• yEnc homepage
• An explanation of some of the technical problems with yEnc
• "Why yEnc is bad for Usenet"
• "What's wrong with yEnc"