In a hybrid peer-to-peer file sharing network including a receiver peer and a provider peer, the receiver sends the provider a ticket [710] obtained from a server authorizing the receiver to obtain a data object O. The receiver obtains a root value of a hash tree for the object, verifies its digital signature, and sends the provider peer a request for a block of data object O and a request for a corresponding set of hash values from the hash tree [714]. The receiver receives from the provider peer the block of O and the corresponding set of hash values of the hash tree [716] that do not contain any hash value in the local hash tree. The receiver sends the provider an acknowledgement of receipt [718], obtains a block key from the provider [720], decrypts the block, verifies the integrity of the block using the subset of hash values and the local hash tree for O, and updates the local hash tree by adding the subset of hash values to the local hash tree, as well as any newly calculated hash values [722]. The provider may submit to a server the acknowledgements as proof of its service to the receiver.