[tor-bugs] #31589 [Core Tor/Tor]: hs-v3: Simplify decrypt_desc_layer interface

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#31589: hs-v3: Simplify decrypt_desc_layer interface
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 Reporter:  asn                                |          Owner:  (none)
     Type:  defect                             |         Status:  new
 Priority:  Medium                             |      Milestone:  Tor:
                                               |  unspecified
Component:  Core Tor/Tor                       |        Version:
 Severity:  Normal                             |     Resolution:
 Keywords:  tor-hs easy refactoring tech-debt  |  Actual Points:
Parent ID:                                     |         Points:
 Reviewer:                                     |        Sponsor:
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Comment (by ltbringer):

 `desc` is passed down to `build_secret_key_iv_mac` -> `build_kdf_key` ->
 `build_secret_input`.

 That means, either we:

 1. Remove `desc` and provide `desc->plaintext_data.blinded_pubkey`,
 `desc->subcredential` and `desc->plaintext_data.revision_counter`
 2. Ditch encrypted_blob and encrypted_blob_size as arguments and get them
 off desc. (same as you suggest)

 My limited experience says, it would be neater to just pass `desc` but I
 would like to know why that wasn't your preference as either solutions are
 easy.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31589#comment:4>
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