The Type1 PostScript font is probably the most widely spread font format in the UNIX world.
A Type1 font program is actually a special case of a PostScript language program. The PostScript interpreter renders the font intelligently, in a device-independent manner. This allows a font developer to create one font program that can be rendered on a wide variety of devices and at many different resolutions.
A Type1 font program consists of a clear text (ASCII) portion, and an encoded and encrypted portion. The PostScript language commands used in a Type1 font program must conform to a much stricter syntax than the “normal” PostScript language programs do. Type1 font programs can include special “hints” that make their representation as exact as possible on a wide variety of devices and pixel densities.
For complete reference, see http://vrr.ucw.cz/doc/T1Format.pdf.
A Type1 font program should be a 7-bit ASCII data stream when it is sent to a PostScript interpreter. However, the programs are not always stored in this way on the host system. In environments where disk space is a concern, the files are compressed according to some scheme to reduce their size on the host system, but they need to be decompressed before they can be understood by a PostScript interpreter.
Type1 font programs are encrypted. That is, most of the actual program file has been reduced to an unreadable form that is decoded by the PostScript printer before it is executed. The encrypted data is in hexadecimal form, as a stream of digits. These digits are preceded by clear-text PostScript language code, and might have a line or two of clear-text PostScript language at the end as well.