Abstract: Signcryption scheme combines digital signature and encryption functions in a logical manner.In a signcryption scheme，messages can be sent in a confidential and authenticate way，which is more efficient than traditional“signature-then-encryption” method.This paper presents a new identity based signcryption scheme with both forward security and public verifiability.At last，the security properties are analyzed，the scheme is proved secure in the random oracle.

Key words: signcryption, forward security, public verifiability, identity based cryptography

摘要： 签密能够在一个合理的逻辑步骤内同时实现数字签名和加密两项功能，因此可以以一个更高效、更节约的方式保证消息秘密而认证的传输。利用双线性对提出了一个基于身份的签密方案，新方案能同时提供前向安全性和公开验证性，并且在随机预言模型下是可证安全的。

关键词: 签密, 前向安全性, 可公开验证性, 基于身份的密码体制