A Compression Method Designed for SMTP over TLS

Abstract

TLS (Transport Layer Security) is a well-known protocol used to provide authentication and private communication for application protocols like HTTP (Hypertext Transfer Protocol) and SMTP (Simple Mail Transfer Protocol). The specification of TLS lays down that in the TLS record protocol, data transferred from the upper layer can be compressed before it is encrypted. However, since there are certain restrictions on the transfer of an E-mail, such as the need for text encoding of binary data and the recompression of already compressed data, using the compression mechanism on SMTP over TLS may result in a reduction in the compression performance. In order to solve these problems, this paper introduces a compression method specifically designed for use with SMTP over TLS. In network experiments, compression ratios and file transfer times for three kinds of E-mail were observed, with emulated bandwidth restrictions to represent three typical communication media, and the results show that the proposal method works efficiently especially for narrow bandwidth networks.