Patent ID: 8433892

Claim:
A method for evaluating a probability of an observation sequence stored at a client with respect to a hidden Markov model (HMM) stored at a server, wherein the client has a decryption key and an encryption key of an additively homomorphic cryptosystem, and the server has the encryption key, comprising the steps of: determining, for each state of the HMM, an encryption of a log-probability of a current element of the observation sequence; determining, for each state of the HMM, an encryption of a log-summation of a product of a likelihood of the observation sequence based on a previous element of the observation sequence and a transition probability to a corresponding state of the HMM, wherein the determining uses a secure multiparty computation using at least one property of additive homomorphism (H-SMC); determining an encryption of a log-likelihood of the observation sequence for each state as a product of the encryption of a log-summation and an encryption of a corresponding log-probability of the current element of the observation sequence; and determining an encryption of the log-probability of the observation sequence based on the log-likelihood of the observation sequence for each state, wherein steps of the method are performed by the server.