117 lines
5.3 KiB
Markdown
117 lines
5.3 KiB
Markdown
# BIP39 Import
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- there must be 12, 16 or 24 words in your mnemonic
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- we have only the English word list
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- ~~we do not support BIP39 passwords during import~~ (full support added in version 2.0.0)
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# XPRV Import
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- we can import a BIP32 HD-wallet root private key in XPRV format
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- it's assumed to be top-level, and we don't store the parent fingerprint or depth value
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- SLIP-132 format HD-wallet keys are also supported (xprv/yprv/zprv), but we strip
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the implied address format
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# PIN Codes
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- 2-2 through 6-6 in size, numeric digits only
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- pin code 999999-999999 is reserved (means 'clear pin')
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# Backup Files
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- we don't know what day it is, so meta data on files will not have correct date/time
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- encrypted files produced cannot be changed, and we don't support other tools making them
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# Micro SD
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- cards up to 32G are supported
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- we do not guarantee to support all cards ever made, or yet to be made
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- we recommend 8G cards or smaller, since our storage needs are very modest
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# Signing / Wallet Types
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- with Electrum, we support classic payment addresses (p2pkh), Bech32 Segwit and P2SH/Segwit
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- however, each wallet must be of a single address type; cannot be mixed (their limitation)
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- the same Coldcard could be used in each of the three modes (we don't care about address format)
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- with Bitcoin Core (version 0.17?), we can do PSBT transactions, which support all address types
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- we don't support coinbase transactions, so don't mine directly into a Coldcard wallet
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# Max Transaction Size
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- we support transactions up to 384k-bytes in size when serialized into PSBT format
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- bitcoin limits transactions to 100k, but there could be large input transactions
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inside the PSBT. Reduce this by using segwit signatures and provide only the
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individual UTXO ("out points").
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- we can handle transactions with up to 20 inputs to be signed at one time.
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- a maximum of 250 outputs per transaction is supported (will attempt more if memory allows)
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# P2SH / Multisig
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- only one signature will be added per input. However, if needed the partly-signed
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PSBT can be given again, and the "next" leg will be signed.
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- we do not support PSBT combining or finalizing of transactions involving
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P2SH signatures (so the combine step must be off-device)
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- we can sign for P2SH and P2WSH addresses that represent multisig (M of N) but
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we cannot sign for non-standard scripts because we don't know how to present
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that to the user for approval.
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- during USB "show address" for multisig, we limit subkey paths to
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16 levels deep (including master fingerprint)
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- max of 15 co-signers due to 520 byte script limitation in consensus layer with classic P2SH
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- we have space for up to 8 M-of-3 wallets, or a single M-of-15 wallet. YMMV
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- only a single multisig wallet can be involved in a PSBT; can't sign inputs from two different
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multisig wallets at the same time.
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- we always store xpubs in BIP32 format, although we can read SLIP132 format (Ypub/Zpub/etc)
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- change outputs (indicated with paths, scripts in output section) must correspond to
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the active multisig wallet, and cannot be used to describe an unrelated (multisig) wallet.
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- derivation path for each cosigner must be known and consistent with PSBT
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- fixed: XFP values (fingerprints) for each of the co-signers must be unique (limitation removed)
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# SIGHASH types
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- only `SIGHASH_ALL` is supported at this time
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- in time, we will add support for others, especially to support Coinjoin usage
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# U2F Protocol / Web Access to USB / WebUSB
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- we do not support U2F protocol, WebUSB or any other means for random websites to talk to us
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- only native desktop/mobile apps, or helpers for those, will be able to talk USB to Coldcard
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# Policy Stuff
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- Coldcard will, by default, reject any txn that pays a fee of more than 10% of its total
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value to miners. This limit is a setting: 10% (default), 25%, 50% or 'no limit'.
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- Fees over 5% (was 1%) are shown as warnings.
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# Developer / Source Code
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- source code can probably only be compiled and developed on Mac OS and Linux
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- we have very limited time to support other devs getting their setups working
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# Change Outputs
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We will hide transaction outputs if they are "change" back into same wallet, however:
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- PSBT must specify BIP32 path in corresponding output section for us to treat as change
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- for p2sh-wrapped segwit outputs, redeem script must be provided when needed
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- any incorrect values here are assumed to be fraud attempts, and are highlighted to user
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- the _redeemScript_ for `p2wsh-p2sh` is optional, but if provided must be
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correct, ie: 0x00 + 0x20 + sha256(_witnessScript_)
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- the _witnessScript_ in a `p2wsh-p2sh` is not optional.
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- depending on the address type of the output, different values are required in the
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corresponding output section, as follows
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- `p2pkh`: no _redeemScript_, no _witnessScript_
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- `p2wpkh-p2sh`: only _redeemScript_ (which will be: `0x00 + 0x14 + HASH160(key)`)
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- `p2wpkh`: no _redeemScript_, no _witnessScript_
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- `p2sh`: _redeemScript_ that contains the a multisig script, ending in 0xAE
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- `p2wsh-p2sh`: _redeemScript_ (which is: `0x00 + 0x20 + sha256(witnessScript)`), and
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_witnessScript_ (which contains the multisig script)
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- `p2wsh`: only _witnessScript_ (which contains the actual multisig script)
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# Derivation Paths
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- key derivatation paths must be 12 or less in depth (`MAX_PATH_DEPTH`)
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