xpubcache: allow choosing if xpub computation should be repeated #1536
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Beerosagos
approved these changes
Aug 19, 2025
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| /// Derives an xpub from the root xpub using the provided keypath. | ||
| fn from_keypath(keypath: &[u32]) -> Result<Self, ()>; | ||
| fn from_keypath(keypath: &[u32], compute: Compute) -> Result<Self, ()>; | ||
| } | ||
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| /// Implements a cache for xpubs. Cached intermediate xpubs are used to derive child xpubs. |
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Unrelated to the change, but I think that the cache_keypath() in the comment should be changed to add_keypath()
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Added separate commit.
| @@ -17,12 +17,18 @@ use super::keystore; | |||
| use crate::bip32; | |||
| use alloc::vec::Vec; | |||
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| #[derive(Copy, Clone)] | |||
| pub enum Compute { | |||
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nit: Maybe it could be useful to add a comment here (or somewhere else) explaining that this is used as an additional bitflips check for sensitive operations
End-goal: reduce the number of secure chip ops when signing a BTC transaction, to reduce the chance of going over the Optiga chip's "rate limit", which induces throttling. By default keystore::get_xpub computed the xpub twice, to mitigate potential bitflips, which could be bad when delivering the wrong xpub (or derivatives) to the host. When signing a transaction however, one does not need the extra protection - if there is a bit flip, the resulting signature will be invalid. This commit reduces the number of secure chip ops needed when the bitflip mitigation is not required. The existing method `get_xpub` was renamed so the compiler can tell us all the instances where we need to decide between one or the other.
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End-goal: reduce the number of secure chip ops when signing a BTC transaction, to reduce the chance of going over the Optiga chip's "rate limit", which induces throttling.
By default keystore::get_xpub computed the xpub twice, to mitigate potential bitflips, which could be bad when delivering the wrong xpub (or derivatives) to the host.
When signing a transaction however, one does not need the extra protection - if there is a bit flip, the resulting signature will be invalid.
This commit reduces the number of secure chip ops needed when the bitflip mitigation is not required.
The existing method
get_xpubwas renamed so the compiler can tell us all the instances where we need to decide between one or the other.