Add entropy command: derive raw BIP-85 entropy at any path

[akarve]

Summary

• New bipsea entropy command: a developer hatch that derives raw BIP-85 entropy (HMAC-SHA512("bip-entropy-from-k", k)) at any fully hardened path, for prototyping and testing new applications before they have a named --application (e.g. the age proposal in bip-85: add example use for age key derivation bitcoin/bips#2174).
• -p/--path takes the raw path (', h, or H hardened markers). -n truncates to the first n bytes (default 64, matching the spec's DERIVED ENTROPY lines). -d instead reads n bytes from the BIP85-DRNG for applications that consume more than 64 bytes. -x/pipe input matches derive.
• Requires fully hardened paths per the spec; warns on stderr when the path does not begin with m/83696968'.
• Tests pin the command to BIP-85 spec vectors (Test case 1, Test case 2, the HEX 64-byte vector, and the 80-byte DRNG vector) and cross-check entropy against derive -a hex at 16/32/64 bytes.
• Fixes a pre-existing test_bad_n typo that invoked a nonexistent entropy command and passed vacuously (any unknown command prints "Error").

Example

bipsea validate -m "$MNEMONIC" | bipsea xprv | bipsea entropy -p "m/83696968'/128169'/32'/0'" -n 32

Test plan

• poetry run pytest -n auto -m "" — 451 passed, 1 xfailed (known spec xfail)
• isort, black, flake8 clean
• Manual smoke: spec Test case 1 vector, HEX 32-byte path, DRNG 80-byte vector, off-purpose warning

Made with Cursor