Problems with UUencoded Transfers

Problems with UUencoded Transfers

UUencoding is an algorithm for converting binary (8-bit) data into a sequence of 7-bit characters. It was designed to assist in the transport of binary files over communications mediums (like Netnews and early e-mail systems) which could not directly transport raw binary data. UUencode was first developed for Unix systems (and was used in the UUCP -Unix to Unix Copy- subsystem) and was later ported to many other platforms.

UUencode works simply by picking off the binary data several bits at a time, and using that numeric value as an offset in a list of designated characters. Obviously, to interoperate among different systems, the list of characters used (in the lookup table) must be consistent.

Herein lie the problems. Some early uuencode implementations allow a space as one of the replacement characters. This introduces problems when some e-mail (and other) transports truncate trailing spaces from message lines.

Further, other implementations replaced the space with a "`" character, introducing incompatibilities among some implementations.

Even more of a basic problem are that several of the characters used in all uuencode implementations do not map well to EBCDIC characters. This causes problems when e-mail messages with uuencoded attachments get transformed through BITNET (EBCDIC) gateways.

For these reasons (and others) the developers of the MIME e-mail standard developed an encoding algorithm called "BASE64" - identical in procedure to uuencode, but using a carefully chosen set of standard characters designed to be transportable through all known gateways.

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