RepositorySimulator._compute_hashes_and_length is broken

[jku]

EDIT: Every test that uses RepositorySimulator._compute_hashes_and_length = True is currently broken because :

• the simulator signs at request time
• ecdsa signatures are not deterministic
• hashes/length calculation is done over the whole file (so it includes these changing signatures)

This should get fixed if any option of #130 is implemented

Original report was :

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test_snapshot_rollback_with_local_snapshot_hash_mismatch() does not seem right:

• the metadata changes in the test seem valid, yet client fails refresh
• test claims in comments to do a target version rollback but does not?
• client actually fails because length and hash are incorrect?

I can't quite see what the issue is.

We should

• find the root cause here
• fix the test
• add a simple test that just uses hashes and length in metafiles without any fancy attacks

[jku]

find the root cause here

oh, it's likely the combination of:

• RepositorySimulator signing at request time
• using ecdsa keys that are not "deterministic"

the hashes/length are over the whole file so include signatures.

This (the fact that making a mistake like this is so easy) is certainly a major downside to signing at request time so we may have to reconsider that decision... Still, maybe switching to a different default key type would also work. I originally only chose ecdsa because they are fast to generate (unlike rsa).

[jku]

I filed an issue for switching the signing keytype (or otherwise solving the underlying issue).

That said, the test is still completely wrong: it claims to test a targets rollback but does not actually try to do one.

[AdamKorcz]

Should this remain open, @jku?

[jku]

yeah, that makes sense: currently client fails as expected but for wrong reasons.

Once #131 is implemented (and #130 is fixed) we have more confidence that the failure happens for right reason

[jku]

test_new_targets_hash_mismatch() is broken because of this as well: If any return values had been checked that would have been visible