Base32: Difference between revisions

This article is about the content encoding scheme. For the positional numerical system, see Base 32.

Base32 is a base 32 transfer encoding using the twenty-six letters A–Z and six digits 2–7. Its closest encoding relation is Base30 that is used by the Natural Area Code.

Primarily Base32 is used to encode binary data, but is able to encode binary text like ASCII.

Software

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.

Base32 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.

Advantages

Base32 has number of advantages over Base64:

1. 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.
2. The result can be used as file name because it can not possibly contain '/' symbol which is usually acts as path separator in Unix-based operating systems.
3. 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'.)
4. A result without padding can be included in a URL without encoding any characters.

Disadvantages

Base32 representation takes roughly 20% more space than Base64.

Length of Base64 and Base32 notations as percentage of binary data

	Base64	Base32
8-bit	133%	160%
7-bit	117%	140%

RFC 4648 Base32 alphabet

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.

The RFC 4648 Base 32 alphabet

Value	Symbol		Value	Symbol		Value	Symbol		Value	Symbol
0	A		9	J		18	S		27	3
1	B		10	K		19	T		28	4
2	C		11	L		20	U		29	5
3	D		12	M		21	V		30	6
4	E		13	N		22	W		31	7
5	F		14	O		23	X
6	G		15	P		24	Y
7	H		16	Q		25	Z
8	I		17	R		26	2		pad	=

Alternative versions

z-base-32

z-base-32 is a Base32 encoding designed to be easier for human use and more compact. It includes 1, 8 and 9 but excludes l, 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.

Crockford's Base32

Another alternative design for Base32 is created by Douglas Crockford, who proposes using additional characters for a checksum.[1] 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.

Libraries to encode binary data in Crockford's Base32 are available in a variety of languages.

Crockford's Base32 alphabet

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
2	2	2		18	J	j J
3	3	3		19	K	k K
4	4	4		20	M	m M
5	5	5		21	N	n N
6	6	6		22	P	p P
7	7	7		23	Q	q Q
8	8	8		24	R	r R
9	9	9		25	S	s S
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

Electrologica

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).

base32hex

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.

The "Extended Hex" Base 32 Alphabet

Value	Symbol		Value	Symbol		Value	Symbol		Value	Symbol
0	0		9	9		18	I		27	R
1	1		10	A		19	J		28	S
2	2		11	B		20	K		29	T
3	3		12	C		21	L		30	U
4	4		13	D		22	M		31	V
5	5		14	E		23	N
6	6		15	F		24	O
7	7		16	G		25	P
8	8		17	H		26	Q		pad	=

Video games

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).

See also

• Base64
• Base16
• Binary-to-text encoding for a comparison of various encoding algorithms

References

• RFC 4648