Decode() performance fix #227
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This is part of a push to support larger files. The focus is the switch
to using Uint8Array to store binary data. But also includes:
- When running on Node, use Buffer.from() for hex string conversions.
- To avoid large buffer copy, signedMsg as been replaced by an object
containing iv, encrypted, and hmac.
- hmac calculation has changed so it avoids copying (possibly very
large) encrypted data. See signDigest() in lib/codec.js.
- Minor cleanup
Handling hex encode/decode at the input/output boundaries and using
Uint8Array internally for representing binary data has these benefits:
- More memory efficient, allows processing of 2x larger files.
- Aligns with cryptographic best practices: hashing is now performed
on raw binary data (Uint8Array) instead of hex strings.
- Behavior is (mostly) unchanged
- scripts/index_template.html textContent is not implemented and
needs to be redesigned.
makes unnamed function more self documenting
Also removed use of recursion to improve readability (and debugability). As a bonus, function is actually shorter (LoC AND lines of text)
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Summary
codec.js/decode() may calculate encryptedDataHash multiple times. calculatedHMAC is based on encryptedDataHash which can be arbitrarily large. Recalculating this hash when the data hasn't changed is a performance bug. The fix is to calculate the hash once. While reviewing this change the use of recursion was replaced with explicit retries.
Fixes
Fixes #226
Details
Testing
I manually tested node encrypt, node decrypt, and HTML wrapper decrypt.
It's not clear to me exactly how I could test the backwards compatible password hashes. Additional testing is recommended.
Notes for Reviewers
Multiple hashing has been around a while, but it was not easy to address before PR #219. I'd say at that point the performance issue became a bug because it was fixable.
Probably variable names 'hashedPassword2' and 'hashedPassword3' could be improved. I assigned them in the order they were used, but:
May be confusing.