Signcryption provides confidentiality and authenticity efficiently;it can be used to design compact communication protocol.Arbitration mechanism is used for settling disputes in signcryption

but the information that the judge gets also brings some security problems.This paper points out two problems:in some scheme

the arbitrator can decrypt all the signcryptions of a receiver while he gets some kinds of arbitration message;in another schemes

the arbitration mechanism cannot protect the integrity of plaintext.Analyze the two kinds of problems and concludes their reasons separately

we proposed a resolvent that can solve the two problem by changing a secure arbitration message.Based on the attack and analysis

this paper proposes a secure arbitral signcryption (SASC) scheme and proves its IND-CCA2 security and UF-CMA security in random oracle model.Furthermore

SASC is a securely arbitral signcryption scheme

it can protect the integrity of plaintexts by an arbitration message associated with plaintext;and the scheme can resist decryption attacks of arbitrator

even he gets the arbitration message.SASC does not increase computation nor communication overloads;it has no limitation to the length of plaintext

which makes SASC more convenient.Proofs and analysis show that SASC is an efficient and secure scheme.