Base32 is a base-32 transfer encoding using the twenty-six letters A-Z and six digits 2-7.
Base32 is a notation for encoding arbitrary byte data using a restricted set of symbols which can be conveniently used by humans and processed by old computer systems which only recognize restricted character sets. It comprises a symbol set made up of 32 different characters, as well as an algorithm for encoding arbitrary strings using 8-bit characters into the Base32 alphabet. This uses more than one 5-bit Base32 symbol for each 8-bit input character, and thus also specifies requirements on the allowed lengths of Base32 strings (which must be multiples of 40 bits). The Base64 system, in contrast, is closely related but uses a larger set of 64 symbols.
Base32 has three main advantages over Base64:
- The resulting character set is all one case (usually represented as uppercase), which can often be beneficial when using a case-insensitive filesystem, spoken speech, or human memory.
- The alphabet was selected to avoid similar-looking pairs of different symbols, so the strings can be accurately transcribed by hand. (For example, the symbol set omits the symbols for 1, 8 and zero, since they could be confused with the letters 'I', 'B', and 'O'.)
- The result can be included in a URL without encoding any characters.
Base32 representation takes roughly 20% more space than Base64.
The most widely used Base32 alphabet is defined in RFC 4648. It uses an alphabet of A–Z, followed by 2–7. 0 and 1 are skipped due to their similarity with the letters O and I (thus "2" actually has a numerical value of 26).
In some circumstances padding is not required or used. RFC 4648 states that padding MUST be used unless the specification of the standard referring to the RFC explicitly states otherwise. Excluding padding is useful when using base32 encoded data in URL tokens or file names where the padding character could pose a problem.
z-base-32 is a Base32 encoding designed to be easier for human use and more compact. It includes 8 and 9 but excludes v and 2. It also permutes the alphabet so that the easier characters are the ones that occur more frequently. It compactly encodes bitstrings whose length in bits is not a multiple of 8, and omits trailing padding characters. z-base-32 was used in Mnet open source project, and is currently used in Phil Zimmermann's ZRTP protocol, and in the Tahoe-LAFS open source project.
Another alternative design for Base32 is created by Douglas Crockford, who proposes using additional characters for a checksum. It excludes the letters I, L, and O to avoid confusion with digits. It also excludes the letter U to reduce the likelihood of accidental obscenity.
|Value||Encode Digit||Decode Digit||Value||Encode Digit||Decode Digit|
|0||0||0 o O||16||G||g G|
|1||1||1 i I l L||17||H||h H|
|10||A||a A||26||T||t T|
|11||B||b B||27||V||v V|
|12||C||c C||28||W||w W|
|13||D||d D||29||X||x X|
|14||E||e E||30||Y||y Y|
|15||F||f F||31||Z||z Z|
An earlier form of base 32 notation was used by programmers working on the Electrologica X1 to represent machine addresses. The "digits" were represented as decimal numbers from 0 to 31. For example, 12-16 would represent the machine address 400 (= 12*32 + 16).
Triacontakaidecimal is another alternative design for Base 32, that extends Hexadecimal in a more natural way. First proposed by Christian Lanctot, a programmer working at Sage software, in a letter to Dr.Dobbs magazine in March 1999 as a proposed solution for solving the Y2K bug and referred to as "Double Hex". RFC 4648 uses base32hex as name for this encoding deployed in RFC 2938.
Unlike many other base 32 notation systems Triacontakaidecimal is contiguous and includes characters that may visually conflict. With the right font it is possible to visually distinguish between 0, O and 1, I. Other fonts are unsuitable because the context that English usually provides is not provided by a notation system that is expressing numbers. However, the choice of font is not controlled by notation or encoding which is why it's risky to assume a distinguishable font will be used.
Before NVRAM became universal, several video games for Nintendo platforms used base 32 numbers for passwords. These systems, like Natural Area Code, omit vowels to prevent the game from accidentally giving a profane password. Thus, the characters are generally some minor variation of the following set: 0-9, B, C, D, F, G, H, J, K, L, M, N, P, Q, R, S, T, V, W, X, Y, Z, and some punctuation marks. Games known to use such a system include Mario Is Missing!, Mario's Time Machine, Tetris Blast, and The Lord of the Rings (Super NES).