Patent ID: 8160966

Claim:
A digital cash implementing method providing digital cash tokens for an electronic cash system containing a certificate authority, a bank, and an issuer of digital cash tokens, said method comprising the steps of: a. said certificate authority providing at least two pairs of certified keys to a user including a master pair having a private and a public key and at least a pseudonym pair having a private and public key; b. said user storing said private master and pseudonym private keys as a secret, said user encrypting a value X using a pseudonym public key of said user, said user signs using said user master private key the following: a user identification, and said encrypted value X; and shows said signed user identification, said encrypted value X to said bank and requests said bank to issue digital cash tokens of a particular face value; c. said bank decrementing said face value from a bank account of said user associated with a real identity of said user, signing encrypted value X using said bank private key, and sending signed encrypted value X to issuer of digital cash tokens and requests the issue of digital cash token with said face value; d. generating a random number by issuer of digital cash tokens upon receipt of said bank request, combining said random number with said encrypted value X to obtain combined value Y, signing said combined value Y using private key of digital cash token of said face value, and sending signed said combined value Y and said random number to said bank using a secure channel; e. said bank encrypting said combined value Y and said random number using said user's master public key, and sending said encrypted combined value Y and said random number to said user; f. said user decrypting said encrypted combined value Y and said random number using private master key of said user, and uses said pseudonym private key of said user on said combined value Y to obtain combined said value X and said random number signed with private key of digital cash token of said face value, and uses said value X, said random number and said combined of said value X and said random number signed with private key of digital cash token of said face value as a digital cash token; and, g. said user verifying said signature on digital cash token using public key of digital cash token of said faced value, said value X and said random number, and spend said digital cash token in any shop using any pseudonym pair of keys.