Is it possible to recalculate the InChI out of an InChIKey? NO!
The InChIKey is the hashed representation of its InChI. The hashing makes it impossible to go backwards from the InChIKey to the original InChI. The “Resolver project” was started to find a solution.
The goal of Resolver is to find a specific InChIKey by running a search over all available databases to get the related InChI being. Resolver uses publicly accessible databases that store InChIs and their related InChIKeys to resolve a key into its related InChI. This includes not only the original structure but also additional data, references, or publications linked to the key. The databases may be spread all over the Internet.
The technique developed in this project can not only be used to resolve InChIKeys, it has the potential to become a general tool for searches over distributed database systems.
More information and links. to download Resolver can be found HERE.