keys: VerifyingKey.precompute() works for keys built from bytes, PEM or DER - #382
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keys: VerifyingKey.precompute() works for keys built from bytes, PEM or DER#382fametrano wants to merge 1 commit into
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VerifyingKey.from_string built the public point without the curve order, so on the Weierstrass curves precompute() failed with AssertionError for every key built from bytes, PEM or DER, the last two going through from_string. A verifying key obtained from a SigningKey, or from signature recovery, carries the order and could be precomputed. Pass the order to PointJacobi.from_bytes and test precompute() after each of the four constructions.
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On the Weierstrass curves,
VerifyingKey.precompute()raisesAssertionErrorfor every key built withfrom_string,from_pemorfrom_der. On 0.19.2:precompute()SigningKey.from_secret_exponent(...).verifying_keyVerifyingKey.from_string(raw)/from_string(compressed)AssertionErrorVerifyingKey.from_pem(...)/from_der(...)AssertionErrorCause:
from_stringcallsPointJacobi.from_byteswithoutorder, sopoint.order()isNone;precompute()then hitsassert orderin_maybe_precompute.from_pemandfrom_dergo throughfrom_string. Keys from aSigningKeyor from signature recovery carry the order and are not affected; EdDSA keys take a separate branch.Fix: pass
order=curve.order(one line). Test:precompute()thenverify()after each of the four constructions; it fails on master and passes with the fix. Full suite: 2040 passed.The docstring says to call
precompute()when verifying hundreds of signatures under one key, which is exactly the caller who has the key as bytes, PEM or DER. Measured on secp256k1, a verification drops from about 1057 µs to 501 µs with the table.