When my WordPress installation failed to update recently, it spat out this error:
The authenticity of wordpress-5.2.4-no-content.zip could not be verified as no signature was found.
1. Delete the .maintenance file. [Hint: It’s a hidden file in ~/wp]
2. Check file permissions.
3. Add your FTP account details to WordPress config file.
4. Update WordPress manually. [This option worked for me.]
If you have other tips, please share them in the comments box.