Certified e-mail delivery with DSA receipts

In this paper we present two variant protocols DSA-CEMD1 and DSA-CEMD2 for certified e-mail delivery with DSA receipts. The protocols are based on a cryptographic primitive called Verifiable and Recoverable Encryption of a Signature (VRES) and are capable of achieving non-repudiation and strong fairness security properties. The novel design of the VRES primitive allows efficiency improvements in comparison with the related certified e-mail delivery protocols based on similar primitives. The protocols employ the services of an off-line and invisible trusted third party (TTP) only in case of dispute. In DSA-CEMD1 the content of the e-mail message is not revealed to the TTP during possible recovery and this is achieved at the cost of some additional cryptographic operations. In DSA-CEMD2 the confidentiality of the message is not protected from the TTP, but the protocol is slightly more efficient.