Abstract: A new key exchange protocol using linear encryption based on short group signature is proposed in this paper. Typically, a short group signature system includes six steps: setup, join, sign, verify, open and revocation. It can provide conditional privacy to group members. The key exchange phase is added into short group signature system so that short group signature system may offer confidentiality after the new key exchange phase. The proposed protocol could implement key exchange between TA(trust authority) and a group member. With the help of TA, the seed of session key can be exchanged between two group members according to this protocol. The following communication can be encrypted by symmetric encipherment algorithm using the exchanged key after key exchange phase. No more parameters is introduced into short group signature system by proposed protocol, which reduces the difficulty in system management. X.509 certification or PKI is unnecessary in proposed protocol, which keeps the conditional privacy of short group signature. Key is exchanged in only two communications, which reduces network delay and congestion. Security analysis proves that the proposed protocol resists tampering attack, impersonal attack, replay attack and man-in-the-middle attack. It provides confidential to short group signature system, which makes short group signature system more suitable for VANET, trust computing and cloud computing.