base.js

Fast base encoding / decoding of any given digits map.

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

Some digits map

Base	Digits
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 digits map and will decode as 8 bits. The other characters depend upon the base. For example, base58 packs roughly 5.858 bits per character.

This means the encoded string 000f (base16, i.e., 0-f) 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.

To use in browser

browserify -r ./src/index:base -o base.js && minify -o base.min.js base.js && rm base.js

Source

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

Heptazhou / base.js