urbit/bippy-scratch.md

## NOTE
The below requires norsyr's fix to `decompress-point` in order to work.

## Working with BTC RPC Library
```
:btc-node-hook|command [%credentials 'http://127.0.0.1:18443' 'poopman' 'chAiM31eeJ1MK3y8BC3mR9q2']
:btc-node-hook|action [%get-block-count ~]
```

## btc-address
**Import lib; optionally set up env**
```
=btca -build-file %/lib/btc-address/hoon
=bip32 -build-file %/lib/bip32/hoon
=ecc secp256k1:secp:crypto
=xpub "xpub6DnWFmBQfQm1wxvKkCJjXwE6H4v8FTwUuhjDQ9ZpJnFDfhA8Dwmg71yPKyjUE93D2CB6MdnWNvGmwsb3fpd4oRJ2YcyMZoMpLU3BjpmQAny"
=parent-zpub "zpub6rmyMSPvm5aexi2PidLFG5ERHCeNQgT3KrkXT6pEPK82zFntRUE5MqwEZCanG5NPzmDvfJ9vAr6NxzTx9FAPTAEN1JFPcL1M7CXNd5WKcP9"
=zpub "zpub6sLyD5WyhVybzoATevSndC5jmhHjfxKjDA5A21DXzoYUJyFyfUo9cW7WX7veTkKVzHjh2Npvfcm5KTT89go29p3PJtscYH4CiYzVbwV5iJW"
```

**Test child public key from xpub**
```
`@ux`(child-from-xpub:btca xpub 0)
(child-from-xpub:btca xpub (dec (bex 31)))

::  should error as index is too high (hardened key range)
(child-from-xpub:btca xpub (bex 31))
```

**Same, with Jose's bip32 library**
```
`@ux`(compress-point:secp256k1:secp:crypto pub:(derive-public:(from-extended:bip32 xpub) 0))
`@ux`(compress-point:secp256k1:secp:crypto pub:(derive-public:(from-extended:bip32 zpub) 0))

::  get same zpub point as above starting from parent-zpub
`@ux`(compress-point:ecc pub:(derive-public:(derive-public:(from-extended:bip32 parent-zpub) 0) 0))
```

## Deprecated: Sample Child Derivations

**Test xpub parsing**
```
(parse-xpub:btca xpub)
```

**Test addition and ECC point checking**
```
=px (parse-xpub:btca xpub)
=pubk ?~  px  ~  pubk.u.px
(is-point:btca pubk)
(pubkey-to-point:btca pubk)
=index 256
`@ux`(add (lsh 3 4 (big-endian-brap:btca pubk)) index)
```

**Test computing I**
```
(bind px |=(px=parsed-xpub:btca (compute-i:btca px 1)))
```