To deliberately attempt to conceal truth or information from the public

Cover up
To attempt to conceal the truth or information about an illegal or unethical act or situation like crimes,scandals or serious mistakes especially about politicians so that people cannot discover them :

- The congress accused the police to cover up the crime.
- The President lied to cover up his relationships with the woman.
- the CIA wanted to cover up its failure in the aftermath of the events that took place in Riyadh.
- The authorities attempted to cover up the homicide.

Also as a noun
- He suggests in his upcoming memoirs that Reagan was directly involved in a " deliberate " cover-up effort.
- The Food and Drug Administration is currently investigating an alleged cover-up by Hoffman on its adverse effects of the new drug.
- He said I didn't realize they were participating in a cover-up.
- He's is angrily denying that he approved a massive " sea of lies " cover-up in connection with the 1988 downing of an Iranian commercial airliner with 290 people aboard.

Whitewash
To hide mistakes,faults or unpleasant facts about something or someone espeially a government or a politician.

- He claimed that the whole crime was whitewashed.
- this is not to whitewash the actual political practice of the government.
- Japan is accused of whitewashing its history of warfare and imperialism by omitting or minimizing subjects such as the Nanking Massacre in textbooks.[
- Angry protesters whitewashed the offensive billboards.

Also as a noun
- He pledged that there would be no whitewash and that the police would carry out a full investigation...
- the report was a whitewash.
- The official report on the taxes has been condemned as a total whitewash.