[Bug][Critical] Mistaking the source/dst copy in the PackedB2A implementation

[fionser]

Issue Type

Currentness/Accuracy

Modules Involved

MPC protocol

Have you reproduced the bug with SPU HEAD?

Yes

Have you searched existing issues?

Yes

SPU Version

74c6d54

OS Platform and Distribution

MacOS

Python Version

3.9

Compiler Version

No response

Current Behavior?

Basically the copying is wrong here.

https://github.com/secretflow/spu/blob/main/libspu/mpc/cheetah/ot/basic_ot_prot.cc#L133

UTs are passed due to the random masking r = 0 now which is also unsecure.

Standalone code to reproduce the issue

The 1st argument in `SseTranspose` should be the output.

Relevant log output

No response

[fionser]

Thank Jinjin Zhou for finding my awful mistake :(.