fix OBS-studio DTLS failed

[a-wing]

We found use OBS-studio WHIP cannot PeerConnected

package DTLS have problem

We found after this commit have this bug

This PR #496 and this commit after 935283a

Finally we found the problem. But, I'm not sure this have bug

https://github.com/RustCrypto/utils/blob/master/block-padding/src/lib.rs#L176-L216

Maybe, webrtc-rs is using this library incorrectly

binbat/live777#39
binbat/live777#58

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.70%. Comparing base (a97d49e) to head (6ae4033).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #557      +/-   ##
==========================================
- Coverage   61.76%   61.70%   -0.07%     
==========================================
  Files         529      530       +1     
  Lines       48828    48848      +20     
  Branches    12250    12274      +24     
==========================================
- Hits        30161    30141      -20     
- Misses       9532     9544      +12     
- Partials     9135     9163      +28     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[yngrtc]

please fix formatting

[edaniels]

@rainliu, can you comment on why 935283a changed the padding in the first place? I'm not sure I understand the reasoning and this was particularly hard to track down. Thank you!

[rainliu]

dtls dependent crates upgrade to new version, however, incorrect usage of new APIs of those crates causes incompatible PADDING.

aes = "0.8"
cbc = { version = "0.1", features = [ "block-padding", "alloc"] }
ccm = "0.5"

[edaniels]

I see, but how is PKCS7 relevant to DTLS? Does the RFC say somewhere that the padding schemes are equivalent?