xpubcache: allow choosing if xpub computation should be repeated #1536
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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_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.