Patent ID: 8601544

Claim:
A method by which a first machine authenticates an untrusted second machine as a condition to performing or allowing a protected operation for the second machine, comprising: by the first machine, performing a write operation identifying a file of a file system of one of the first machine and the second machine and including an authentication identifier to be stored in the file; subsequently by the first machine, performing a read operation identifying the file and returning a read value, wherein the read operation using either an untrusted mechanism employing the second machine or a trusted mechanism employing the first machine alone or in combination with a trusted management component having privileged system-level access to the file system, wherein the write operation using the trusted mechanism if and only if the read operation uses the untrusted mechanism, or the write operation using the untrusted mechanism if and only if the read operation uses the trusted mechanism; and by the first machine, performing or allowing the protected operation for the second machine only upon the read value returned by the read operation matching the authentication identifier, wherein the first and second machines are virtual machines executing on one or more physical host machines, and wherein the management component is included in a set of virtual machine management components having a pre-established trust relationship with one of the virtual machines.