IIRC files must be readable o+r, directories read and executable o+rx

r is not strictly required for directories, missing read permissions on a directory only prevent you from listing the directory (ls and opendir will fail). To access items in a directory, you only need "cross" (executable) permissions on the directory, and sufficient permissions on the directory items.

For shared libraries (*.so), it actually depends on the OS implementation. Some Unix systems require them to be executable, for others, read permissions are sufficient. On Linux, you can have both variants, depending on the distribution.

Alexander