Z85 Encoder/Decoder (ZeroMQ)

Z85 encodes four bytes into five characters, like any base85, but with a hand-picked alphabet: it avoids the single quote, the double quote, the backslash and the backtick. The reason is practical — the resulting text can be pasted inside a string literal in practically any language, into a configuration file and onto a command line without needing escapes.

Type the text and get the encoding. One restriction comes from the specification: the byte length must be a multiple of four. Unlike Ascii85, Z85 defines no padding for an incomplete final group, and the page refuses rather than inventing one. Anyone encoding arbitrary lengths has to agree padding out of band, together with whatever will decode it.

Its best-known use is CurveZMQ, ZeroMQ's security mechanism, where 32-byte keys become 40 characters — a multiple of four by construction, which explains why the limitation never bothered anyone in its home context. The implementation was checked against the specification vector: bytes 86 4F D2 6F B5 59 F7 5B encode exactly to HelloWorld.