A method, comprising: establishing, by an enclave executed by a trusted execution environment that runs at an untrusted provider, a trusted relationship with a user accessing a user application, wherein the establishment is at least partially based on a trust measurement communicated between the enclave and a certificate authority component associated with the user; associating, by the enclave, one or more access control permissions to a file linked from the user application to a remote file system at the untrusted provider, wherein the one or more access control permissions define one or more parameters of access related to the file and defined by the user for individual users and groups of users, and wherein the file is linked to the remote file system over a secure interface between the user application and the enclave; and providing, by the enclave and to a second user, access to the file, wherein: the providing is in response to a verification that a request for the file from the second user satisfies the one or more access control permissions, the providing is further in response to establishment of a second trusted relationship with the second user, the second user having individual access rights or being part of a group with access rights, and the providing comprises the enclave receiving the file in an encrypted form from the remote file system, decrypting the encrypted file, and sending the file over a protected channel to provide access to the file; characterised in that the remote file system stores: an ACL file for each file, the ACL file storing the access permissions and file owners of the respective file, a group list file storing all groups and a member list file for each user, wherein the member list file stores the group memberships and the group ownerships of the respective user. establishing, by an enclave executed by a trusted execution environment that runs at an untrusted provider, a trusted relationship with a user accessing a user application, wherein the establishment is at least partially based on a trust measurement communicated between the enclave and a certificate authority component associated with the user; associating, by the enclave, one or more access control permissions to a file linked from the user application to a remote file system at the untrusted provider, wherein the one or more access control permissions define one or more parameters of access related to the file and defined by the user for individual users and groups of users, and wherein the file is linked to the remote file system over a secure interface between the user application and the enclave; and providing, by the enclave and to a second user, access to the file, wherein: the providing is in response to a verification that a request for the file from the second user satisfies the one or more access control permissions, the providing is further in response to establishment of a second trusted relationship with the second user, the second user having individual access rights or being part of a group with access rights, and the providing comprises the enclave receiving the file in an encrypted form from the remote file system, decrypting the encrypted file, and sending the file over a protected channel to provide access to the file; the providing is in response to a verification that a request for the file from the second user satisfies the one or more access control permissions, the providing is further in response to establishment of a second trusted relationship with the second user, the second user having individual access rights or being part of a group with access rights, and the providing comprises the enclave receiving the file in an encrypted form from the remote file system, decrypting the encrypted file, and sending the file over a protected channel to provide access to the file; characterised in that the remote file system stores: an ACL file for each file, the ACL file storing the access permissions and file owners of the respective file, a group list file storing all groups and a member list file for each user, wherein the member list file stores the group memberships and the group ownerships of the respective user.