"E-mail Security - How to keep your Electronic Messages Private": E-mail security by Bruce Schneier 1995 (John Wiley & Sons 365 pp.) isbn 0-471-05318-X

PRIVACY AND ELECTRONIC MAIL. The Problem. Encryption. Key Management. Authentication. Certificates. Keeping Your Private Key Private. Odds and Ends. Patents, Governments, and Export Laws. ACHIEVING ELECTRONIC-MAIL PRIVACY. Requirements and Features. Privacy Enhanced Mail (PEM). Pretty Good Privacy (PGP). Comparing PGP and PEM. Attacks Against PGP and PEM. Appendices. Index.