c32check/README.md

Crockford base-32 checksum encoding

# c32check

[Crockford base-32](https://en.wikipedia.org/wiki/Base32#Crockford's_Base32)
encoding library with 4-byte checksum.

This library is meant for generating and decoding addresses on the Stacks
blockchain.

## How it works

Each c32check string encodes a 1-byte version and a 4-byte checksum. When
decoded as a hex string, the wire format looks like this:

```
0      1                             n+1             n+5
|------|-----------------------------|---------------|
version     n-byte hex payload          4-byte hash
```

If `version` is the version byte (a 1-byte `number`) and `payload` is the raw
bytes (e.g. as a `string`), then the `checksum` is calculated as follows:

```
checksum = sha256(sha256(version + payload)).substring(0,4)
```

In other words, the checksum is the first four bytes of the
double-sha256 of the bytestring concatenation of the `version` and `payload`.
This is similar to base58check encoding, for example.

## c32 Addresses

The Stacks blockchain uses c32-encoded public key hashes as addresses.
Specifically, a **c32check address** is a c32check-encoded ripemd160 hash.

---

# Examples

```
> c32 = require('c32check')
{ c32encode: [Function: c32encode],
  c32decode: [Function: c32decode],
  c32checkEncode: [Function: c32checkEncode],
  c32checkDecode: [Function: c32checkDecode],
  c32address: [Function: c32address],
  c32addressDecode: [Function: c32addressDecode],
  versions:
   { mainnet: { p2pkh: 22, p2sh: 20 },
     testnet: { p2pkh: 26, p2sh: 21 } },
  c32ToB58: [Function: c32ToB58],
  b58ToC32: [Function: b58ToC32] }
```

## c32encode, c32decode

```
> c32check.c32encode(Buffer.from('hello world').toString('hex'))
'38CNP6RVS0EXQQ4V34'
> c32check.c32decode('38CNP6RVS0EXQQ4V34')
'68656c6c6f20776f726c64'
> Buffer.from('68656c6c6f20776f726c64', 'hex').toString()
'hello world'
```

## c32checkEncode, c32checkDecode

```
> version = 12
12
> c32check.c32checkEncode(version, Buffer.from('hello world').toString('hex'))
'CD1JPRV3F41VPYWKCCGRMASC8'
> c32check.c32checkDecode('CD1JPRV3F41VPYWKCCGRMASC8')
[ 12, '68656c6c6f20776f726c64' ]
> Buffer.from('68656c6c6f20776f726c64', 'hex').toString()
'hello world'
```

## c32address, c32addressDecode

> **Note**:
> These methods only work on ripemd160 hashes

```
> hash160 = 'a46ff88886c2ef9762d970b4d2c63678835bd39d'
'a46ff88886c2ef9762d970b4d2c63678835bd39d'
> version = c32check.versions.mainnet.p2pkh
22
> c32check.c32address(version, hash160)
'SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7'
> c32check.c32addressDecode('SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7')
[ 22, 'a46ff88886c2ef9762d970b4d2c63678835bd39d' ]
```

## c32ToB58, b58ToC32

> **Note**:
> Common address versions are converted between c32check and base58check
> seamlessly, in order to accommodate Stacks addresses.

```
> b58addr = '16EMaNw3pkn3v6f2BgnSSs53zAKH4Q8YJg'
'16EMaNw3pkn3v6f2BgnSSs53zAKH4Q8YJg'
> c32check.b58ToC32(b58addr)
'SPWNYDJ3STG7XH7ERWXMV6MQ7Q6EATWVY5Q1QMP8'
> c32check.c32ToB58('SPWNYDJ3STG7XH7ERWXMV6MQ7Q6EATWVY5Q1QMP8')
'16EMaNw3pkn3v6f2BgnSSs53zAKH4Q8YJg'
```

```
> b58addr = '3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r'
'3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r'
> c32check.b58ToC32(b58addr)
'SM1Y6EXF21RZ9739DFTEQKB1H044BMM0XVCM4A4NY'
> c32check.c32ToB58('SM1Y6EXF21RZ9739DFTEQKB1H044BMM0XVCM4A4NY')
'3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r'
```