The "crypto" field in backup.json was introduced alongside encryption
support in 2018 to indicate the algorithm (aes128). Over time,
encryption moved into securetar and the field became write-only
metadata — no code reads it to make decisions. With securetar v3, the
field is now actively misleading since the actual encryption algorithm
differs from what "crypto": "aes128" suggests. Remove ATTR_CRYPTO and
CRYPTO_AES128 constants, stop writing "crypto" to new backups, and use
vol.Remove to silently strip the key when loading old backups that
still contain it.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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