This PR fixes multiple issues in the source code to address issues raised by
tests/scripts/check-files.py. Specifically:
* incorrect file permissions
* missing newline at the end of files
* trailing whitespace
* Tabs present
* TODOs in the souce code
The main goal with these tests is to test the bug in question and
they are not meant to test the entire PKCS#1 v1.5 behaviour. To
achieve full test coverage, further test cases are needed.