A method of emulation-based page granularity code signing comprising the steps of: copying guest operating system instructions and associated hash message authentication codes and/or digital signatures of each guest operating instruction from an untrusted guest operating system memory into a trusted host operating system memory; recomputing the hash message authentication codes using a secret key in the trusted host operating system memory; maintaining the secret key in the trusted host operating system memory and inaccessible by the untrusted guest operating system instructions; translating each guest operating system instruction that has a valid hash message authentication code to a set of host operating system instructions; executing the decrypted guest operating system instructions in the trusted host operating system; and modifying the guest operating system memory and registers when the set of translated host operating instructions executes in the trusted host operating system, such that it appears as if the original guest operating system instructions had been executed in the untrusted guest operating system.