关键词: 密钥管理, 组合公钥（CPK）, 种子公/私钥, 标识密钥, 碰撞

Abstract: Combined Public Key（CPK） is an authentication technique which is an independent intellectual property of China. Compared with PKI and IBC, CPK has its particular advantages. However, since the secret key is generated by combining several seeded secret keys, collisions might happen. How to avoid collisions efficiently becomes the linchpin of the development of CPK. After the development and problems of CPK are introduced, two novel methods are put forward to select and combine the seeded public/private keys, which reduces the seeds space evidently with the same level of security. A solution is proposed aiming at two factors which lead to collisions：using block ciphers to map the user identity, produce seeds in accordance with specific rules and restrict the parameters of elliptic curve. The improved CPK system can provide a collision-free key space with a smaller space of seeds, high efficiency, high security, and easy management.

Key words: key management, Combined Public Key（CPK）, seeded public/secret key, identity-key, collision