SQL Server Reporting services migration (2008 to 2012)

We have a SSRS 2008 (not R2) instance with a few hundred reports, and now, on a new machine we have installed a 2012 instance of SSRS. We need to migrate all the reports, while keeping all their rights and privileges, plus the datasources with credentials (some of them have local data sources). Is there a way to achieve this? The high number of reports does not allow us do it manually one by one. We tried to migrate a report, but as I said, the rights and credentials were lost. Any ideas? Thank you in advance!