basE91 is an advanced method for encoding binary data as ASCII characters. It is similar to UUencode or base64, but is more efficient. The overhead produced by basE91 depends on the input data. It amounts at most to 23% (versus 33% for base64) and can range down to 14%, which typically occurs on 0-byte blocks. This makes basE91 very useful for transferring larger files over binary unsafe connections like e-mail or terminal lines.

The encoding/decoding routines have been restructured to be thread-safe, and the syntax of the commandline frontend is more similar to base64 from the GNU coreutils now.

basE91 – Freecode

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