1. Anne, queen of England. An act for giving like remedy upon promissory notes, as is now used upon bills of exchange, and for the better payment of inland bills of exchange. 1704. 3 & 4 Anne, chapter 9.
2. Colin Boyd. Some applications of multiple key ciphers. In Christoph G. Gunther, editor, Advances in Cryptogrophy: EUROCRYPT '88, pages 455–467, Springer-Verlag, 1988.
3. David Chaum, Amos Fiat, and Moni Naor. Untracable electronic cash. In Crypto '88, 1988.
4. David Chaum. Security without identification: transaction systems to make big brother obsolete. Communications of the ACM, 1030–1044, October 1985.
5. Whitfield Diffie and Martin E. Hellman. New directions in cryptography. IEEE Transactions on Information Theory, IT-22:644–654, November 1976.