Binary-to-text encoding

A binary-to-text encoding is a data encoding scheme that represents binary data as plain text. Generally, the binary data consists of a sequence of arbitrary 8-bit byte (a.k.a. octet) values and the text is restricted to the printable character codes of commonly-used character encodings such as ASCII. In general, arbitrary binary data contains values that are not printable character codes, so software designed to only handle text fails to process such data. Encoding binary data as text allows information that is not inherently stored as text to be processed by software that otherwise cannot process arbitrary binary data. The software cannot interpret the information, but it can perform useful operations on the data such as transmit and store.

PGP documentation (RFC 9580) uses the term "ASCII armor" for binary-to-text encoding when referring to Base64.

Conceptually, binary-to-text encoding differs from numeric representation for a numeric base (radix). For example, decimal is a scheme for representing a value as base-10, but it is not a binary-to-text encoding. A binary-to-text encoding could be devised that uses decimal representation for encoded data, but such a system would use only 10 values of a 4-bit encoded sequence, leaving 6 values unused. A more efficient encoding would use all 16 values. This is Base16 which uses hexadecimal for encoding each 4-bit sequence. Notably, because 16 is a power of two, Base16 and hexadecimal are indistinguishable in practice even though they differ conceptually.

Escape encodings such as percent-encoding and quoted-printable also allow for representing arbitrary binary data as text, but in a significantly different way. A binary-to-text encoding involves encoding an entire input sequence whereas an escape encoding allows for embedding binary data in data that is already and inherently text.