Functional encryption (FE) is a novel paradigm for encryption scheme which allows tremendous flexibility in accessing encrypted information.In FE,a user can learn specific function of encrypted messages by restricted functional key and reveal nothing else about the messages.Inner product encryption (IPE) is a special type of functional encryption where the decryption algorithm,given a ciphertext related to a vector x and a secret key related to a vector y,computes the inner product x· y.In this paper,we construct an efficient private-key functional encryption (FE) for inner product with simulation-based security,which is much stronger than indistinguishability-based security,under the External Decisional Linear assumption in the standard model.Compared with the existing schemes,our construction is faster in encryption and decryption,and the master secret key,secret keys and ciphertexts are shorter.