Base 58

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Source code: base58.js, base58check.js

Note that Base 58 is handled automatically by Money Button behind the scenes and it is not necessary to deal with Base 58 directly unless you are building an advanced application.

A Bitcoin address is the hash of a public key. In the early days of Bitcoin, and still often today, users have to copy and paste addresses around, and there is a lot of opportunity to make mistakes. It would be really bad to accidentally send money to the wrong address. So Satoshi used a custom Base 58 encoding scheme for Bitcoin addresses that doesn't allow any confusing characters (no lower case L and no upper case i). In addition, the encoding scheme includes a hash checksum to make errors in copying an address almost impossible.

Base 58

First, let's consider the case without the checksum.

Given any piece of data, we can encode it using this list of 58 characters:

123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz

The way we do that with bsv is as follows. Suppose I have a string "this is my string" which I wish to encode. This is how we encode it into base58:

var str = "this is my string"
var base58 = bsv.encoding.Base58.fromBuffer(Buffer.from(str)).toString()

console.log(base58)
// prints:
// 26St9k2Wa1oUK3T9MYpNXtzr

And this is how we decode it:

var base58 = '26St9k2Wa1oUK3T9MYpNXtzr'
var buf = bsv.encoding.Base58.fromString(base58).toBuffer()

console.log(buf.toString())
// prints:
// this is my string

Base58Check

Because Base58 can still be accidentally mistyped, there is also a format that includes a checksum. A checksum is just a shortened hash of the data that prefixes the data. That way, if the data is accidentally changed, it will no longer match the checksum, and you can know the data has been mistyped.

Suppose again I have a string "this is my string" which I wish to encode. This is how we encode it into base58check:

var str = "this is my string"
var base58check = bsv.encoding.Base58Check.fromBuffer(Buffer.from(str)).toString()

console.log(base58check)
// prints:
// 8AArJ45YvcrtshadAYjNgHtXHRGtA

Notice how the output is a bit longer and is different on the whole. That is because it includes a checksum at the start. But it still consists of the same type of characters - all Base 58 characters.

And this is how we decode it:

var base58check = '8AArJ45YvcrtshadAYjNgHtXHRGtA'
var buf = bsv.encoding.Base58Check.fromString(base58check).toBuffer()

console.log(buf.toString())
// prints:
// this is my string