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docs: refactor and update coins README

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# BIP-44 derivation paths # BIP-44 derivation paths
Each coin uses [BIP-44](https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki) derivation path scheme. If the coin is UTXO-based the path should have all five parts, precisely as defined in [BIP-32](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki). If it is account-based we follow Stellar's [SEP-0005](https://github.com/stellar/stellar-protocol/blob/master/ecosystem/sep-0005.md) - paths have only three parts `44'/c'/a'`. Unfortunately, lot of exceptions occur due to compatibility reasons. Each coin uses [BIP-44] derivation path scheme. If the coin is UTXO-based the path
should have all five parts, precisely as defined in [BIP-32]. If it is account-based we
follow Stellar's [SEP-0005] - paths have only three parts `44'/c'/a'`. Unfortunately,
lot of exceptions occur due to compatibility reasons.
Keys are derived according to [SLIP-10], which is a superset of the BIP-32 derivation
algorithm, extended to work on other curves.
[bip-44]: https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki
[bip-32]: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
[sep-0005]: https://github.com/stellar/stellar-protocol/blob/master/ecosystem/sep-0005.md
[slip-10]: https://github.com/satoshilabs/slips/blob/master/slip-0010.md
## List of used derivation paths ## List of used derivation paths
| coin | curve | getPublicKey | getAddress | sign tx | derivation | note | | coin | curve | path | public node | note |
|----------------|----------------|----------------|------------------|------------------|-----------------|--------------| | -------- | -------- | ------------------ | ----------- | -------------- |
| Bitcoin | secp256k | 44'/c'/a' | 44'/c'/a'/y/i | 44'/c'/a'/y/i | BIP-32 | [1](#Bitcoin) | | Bitcoin | secp256k | `44'/c'/a'/y/i` | yes | [1](#Bitcoin) |
| Ethereum | secp256k | 44'/60'/0' | 44'/60'/0'/0/i | 44'/60'/0'/0/i | BIP-32 | [2](#Ethereum)| | Ethereum | secp256k | `44'/c'/0'/0/a` | yes | [2](#Ethereum) |
| Ripple | secp256k | - | 44'/144'/a'/0/0 | 44'/144'/a'/0/0 | BIP-32 | [3](#Ripple) | | Ripple | secp256k | `44'/144'/a'/0/0` | | [3](#Ripple) |
| Cardano | ed25519 | 44'/1815'/a' | 44'/1815'/a'/{0,1}/i | 44'/1815'/a'/{0,1}/i | [Cardano's own](https://cardanolaunch.com/assets/Ed25519_BIP.pdf)<sup>[4](#Cardano)</sup> | | | Cardano | ed25519 | `44'/1815'/a'/y/i` | yes | [4](#Cardano) |
| Stellar | ed25519 | - | 44'/148'/a' | 44'/148'/a' | SLIP-0010 | | | Stellar | ed25519 | `44'/148'/a'` | | |
| Lisk | ed25519 | 44'/134'/a' | 44'/134'/a' | 44'/134'/a' | SLIP-0010 | | | Lisk | ed25519 | `44'/134'/a'` | | |
| NEM | ed25519 | - | 44'/43'/a' | 44'/43'/a' | SLIP-0010 | [5](#NEM) | | NEM | ed25519 | `44'/43'/a'` | | [5](#NEM) |
| Monero | ed25519 | 44'/128'/a'<sup>[6](#Monero)</sup> | 44'/128'/a' | 44'/128'/a' | SLIP-0010 | | | Monero | ed25519 | `44'/128'/a'` | | |
| Tezos | ed25519<sup>[7](#Tezos)</sup> | 44'/1729'/a' | 44'/1729'/a' | 44'/1729'/a' | SLIP-0010 | | | Tezos | ed25519 | `44'/1729'/a'` | | [6](#Tezos) |
Paths that do not conform to this table are allowed, but user needs to confirm a warning on Trezor. For getPublicKey we do not check if the path is followed by other non-hardened items (anyone can derive those anyway). This is beneficial for Ethereum and its MEW compatibility, which sends `44'/60'/0'/0` for getPublicKey. `c` stands for the [SLIP-44 id] of the currency, when multiple currencies are handled
by the same code. `a` is an account number, `y` is change address indicator (must be
0 or 1), and `i` is address index.
## Notes [slip-44 id]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
1. <a name="Bitcoin"></a> For Bitcoin and its derivatives it is a little bit more complicated. `p` is decided based on the following table: Paths that do not conform to this table are allowed, but user needs to confirm a warning
on Trezor.
| p | type | input script type | ### Public nodes
|-----|--------------|--------------------|
| 44 | legacy | SPENDADDRESS |
| 48 | multisig | SPENDMULTISIG |
| 49 | p2sh segwit | SPENDP2SHWITNESS |
| 84 | native segwit | SPENDWITNESS |
Other `p` are disallowed. `c` has to be equal to the coin's [slip44 id](https://github.com/satoshilabs/slips/blob/master/slip-0044.md) as for every coin. `y` needs to be 0 or 1. Some currencies allow exporting a _public node_, which lets the client derive all
non-hardened paths below it. In that case, the conforming path is equal to the
hardened prefix.
2. <a name="Ethereum"></a> We believe this should be `44'/60'/a'`, because Ethereum is account-based, rather than UTXO-based. Unfortunately, lot of Ethereum tools (MEW, Metamask) do not use such scheme and set `a = 0` and then iterate the address index `i`. Therefore for compatibility reasons we use the same scheme: `44'/60'/0'/0/i` and only the `i` is being iterated. I.e., for Bitcoin's path `44'/c'/a'/y/i`, the allowed public node path is `44'/c'/a'`.
3. <a name="Ripple"></a> Similar to Ethereum this should be `44'/144'/a'`. But for compatibility with other HW vendors we use `44'/144'/a'/0/0`. Trezor does not check if the path is followed by other non-hardened items (anyone can
derive those anyway). This is beneficial for Ethereum and its MEW compatibility, which
sends `44'/60'/0'/0` for getPublicKey.
4. <a name="Cardano"></a> Which allows non-hardened derivation on ed25519. ### Notes
5. <a name="NEM"></a> NEM's path should be `44'/60'/a'` as per SEP-0005, but we allow `44'/60'/a'/0'/0'` as well for compatibility reasons with NanoWallet. 1. <a name="Bitcoin"></a> For Bitcoin and its derivatives it is a little bit more
complicated. `p` is decided based on the following table:
6. <a name="Monero"></a> Actually it is GetWatchKey for Monero. | p | type | input script type |
| --- | --------------- | ----------------- |
| 44 | legacy | SPENDADDRESS |
| 48 | legacy multisig | SPENDMULTISIG |
| 49 | p2sh segwit | SPENDP2SHWITNESS |
| 84 | native segwit | SPENDWITNESS |
7. <a name="Tezos"></a> Tezos supports multiple curves, but Trezor currently supports ed25519 only. Other `p` are disallowed.
2. <a name="Ethereum"></a> We believe this should be `44'/c'/a'`, because Ethereum is
account-based, rather than UTXO-based. Unfortunately, lot of Ethereum tools (MEW,
Metamask) do not use such scheme and set `a = 0` and then iterate the address index
`i`. Therefore for compatibility reasons we use the same scheme.
3. <a name="Ripple"></a> Similar to Ethereum this should be `44'/144'/a'`. But for
compatibility with other HW vendors we use `44'/144'/a'/0/0`.
4. <a name="Cardano"></a> Cardano has a [custom derivation] algorithm that allows
non-hardened derivation on ed25519.
[custom derivation]: https://cardanolaunch.com/assets/Ed25519_BIP.pdf
5. <a name="NEM"></a> NEM's path should be `44'/43'/a'` as per SEP-0005, but we allow
`44'/43'/a'/0'/0'` as well for compatibility reasons with NanoWallet.
6. <a name="Tezos"></a> Tezos supports multiple curves, but Trezor currently supports
ed25519 only.
Sign message paths are validated in the same way as the sign tx paths are. Sign message paths are validated in the same way as the sign tx paths are.
## Allowed values ## Allowed values
For GetPublicKey `a` needs in the interval of \[0, 20]. For GetAddress and signing the longer five-items paths need to have `a` also in range of \[0, 20] and `i` in \[0, 1000000]. If only three-items paths are used (Stellar and Lisk for example), `a` is allowed to be in \[0, 1000000] (because there is no address index `i`). For UTXO-based currencies, account number `a` needs to be in the interval \[0, 20]
and address index `i` in the interval \[0, 1 000 000].
For account-based currencies (i.e., those that do not use address indexes), account
number `a` needs to be in the interval \[0, 1 000 000]