Drop ChannelKeys Private Key Methods #632
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As we drop the requirement that all ChannelKeys expose the private keys used, we should have a way to access the private keys in use when using InMemoryChannelKeys.
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## master #632 +/- ##
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- Coverage 91.26% 91.26% -0.01%
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- Hits 19101 19090 -11
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| /// Gets the local secret key used in HTLC-Success/HTLC-Timeout txn and to_local output | ||
| fn delayed_payment_base_key<'a>(&'a self) -> &'a SecretKey; | ||
| /// Gets the local htlc secret key used in commitment tx htlc outputs | ||
| fn htlc_base_key<'a>(&'a self) -> &'a SecretKey; | ||
| /// Gets the commitment seed | ||
| fn commitment_seed<'a>(&'a self) -> &'a [u8; 32]; |
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Future work, should we move commitment_seed out-of-memory and behind the interface by moving inside chan_utils::build_commitment_secret ? In case of undetected node compromise, access to the commitment seed let you derive revocation secret for future non-yet-existent local commitment transactions ?
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Yea, I think we have to. If you want an external signer to prevent the host from burning all the coins, you need some kind of exchange here, but we'd also need to get the ordering right, like, to call get_commitment_revocation_secret we'd have to first provide a copy of the new commitment transaction.
| @@ -345,17 +333,17 @@ pub trait KeysInterface: Send + Sync { | |||
| /// A simple implementation of ChannelKeys that just keeps the private keys in memory. | |||
| pub struct InMemoryChannelKeys { | |||
| /// Private key of anchor tx | |||
| funding_key: SecretKey, | |||
| pub funding_key: SecretKey, | |||
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I think even for this concrete implementation, it would be better to not make the private key properties public. Perhaps add a test config constraint?
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You need them to be able to sign transactions when handling SpendableOutput events, so there needs to be some way to get at them.
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Don't know the full context, but might it be better to expose a way to use them (e.g. expose a sign_tx method) rather than exposing the keys themselves?
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If the signing only handles in impl for InMemoryChannelKeys, they may not have to be pub, right?
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No, we dont require signing functions for SpendableOutputs events as those are purely external and can happen a month later. eg the use in the tests at https://github.com/rust-bitcoin/rust-lightning/blob/master/lightning/src/ln/functional_tests.rs#L4299
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This isn't quite sufficient for a secure external signer, as we still expose commitment_seed(), but its a nice cleanup after #610 did all the heavy lifting and its a good step.