Decrypts a file this library encrypted and you downloaded.
Two failures, told apart
A secret this library did not produce is refused as malformed. Bytes that
are not the bytes the secret announced are refused as that, separately —
Matrix's attachment encryption carries a SHA-256 of the ciphertext, and
this is that check failing. It means the download was truncated, corrupted
or substituted.
The distinction is worth acting on: the first is a bug upstream of the
download and retrying will not help, the second is a download worth making
again. Neither ever returns partial bytes — the check runs at the end of
the file, and a failure discards everything.
Decrypts a file this library encrypted and you downloaded.
Two failures, told apart
A secret this library did not produce is refused as malformed. Bytes that are not the bytes the secret announced are refused as that, separately — Matrix's attachment encryption carries a SHA-256 of the ciphertext, and this is that check failing. It means the download was truncated, corrupted or substituted.
The distinction is worth acting on: the first is a bug upstream of the download and retrying will not help, the second is a download worth making again. Neither ever returns partial bytes — the check runs at the end of the file, and a failure discards everything.