base-x

Fast base encoding / decoding of any given alphabet using bitcoin style leading zero compression.

WARNING: This module is NOT RFC3548 compliant, it cannot be used for base16 (hex), base32, or base64 encoding in a standards compliant manner.

Example

Base58

var BASE58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var bs58 = require('base-x')(BASE58)

var decoded = bs58.decode('5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr')

console.log(decoded)
// => Uint8Array(33) [
//   128, 237, 219, 220,  17, 104, 241, 218,
//   234, 219, 211, 228,  76,  30,  63, 143,
//    90,  40,  76,  32,  41, 247, 138, 210,
//   106, 249, 133, 131, 164, 153, 222,  91,
//    25
// ]

console.log(bs58.encode(decoded))
// => 5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr

Alphabets

See below for a list of commonly recognized alphabets, and their respective base.

Base	Alphabet
2	01
8	01234567
11	0123456789a
16	0123456789abcdef
32	0123456789ABCDEFGHJKMNPQRSTVWXYZ
32	ybndrfg8ejkmcpqxot1uwisza345h769 (z-base-32)
36	0123456789abcdefghijklmnopqrstuvwxyz
58	123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
62	0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
64	ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
67	ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.!~

How it works

It encodes octet arrays by doing long divisions on all significant digits in the array, creating a representation of that number in the new base. Then for every leading zero in the input (not significant as a number) it will encode as a single leader character. This is the first in the alphabet and will decode as 8 bits. The other characters depend upon the base. For example, a base58 alphabet packs roughly 5.858 bits per character.

This means the encoded string 000f (using a base16, 0-f alphabet) will actually decode to 4 bytes unlike a canonical hex encoding which uniformly packs 4 bits into each character.

While unusual, this does mean that no padding is required and it works for bases like 43.

LICENSE MIT

A direct derivation of the base58 implementation from bitcoin/bitcoin, generalized for variable length alphabets.