Message security

A system operable to electronically transmit a human-readable message securely between a first user using a first terminal and a second user using a second terminal, said system comprising:

• the first terminal and the second terminal, each of the first and second terminals including a counter configured to periodically change a counting value a calculating unit configured to independently generate a key using a seed and said counting value of said counter belonging to the respective terminal;
• said first terminal being configured to electronically transmit an e-mail message in encrypted form together with a dynamic serial number corresponding to said message from the first terminal to the second terminal, said encrypted message being encrypted by means of said key, said dynamic serial number identifying said key;
• said second terminal being configured to receive said message and use said dynamic serial number to identify said key used to encrypt said message and a sequential order of said message;
• and
• said second terminal being configured to receive and store said seed in said second terminal,
• such that said calculating unit of said second terminal is configured to independently generate said key using said dynamic serial number, said seed and said counting value, said second terminal is configured to decrypt said encrypted message using said independently generated key,
• the first and second terminals further being arranged to generate a list of entrusted terminals based on said seed, accept e-mail messages only from registries in said list, sense when the counters thereof are not synchronised and then synchronise the counters.

A computer-implemented method of filtering electronically transmitted e-mail messages from a first user having a first terminal to a recipient being a second user having a second terminal, comprising:

• a) electronically transmitting by a first terminal an e-mail message encrypted into an encrypted form, said encrypted message being encrypted by means of a key generated by a first key generator using a seed;
• b) providing once said second user with said seed for generating a key with a second key generator provided in said second terminal;
• c) generating a list of trusted senders by said second terminal based on a sender-receiver relation generated by said seed;
• and
• d) receiving said encrypted message at said second terminal and handling said received encrypted message in a manner based on said list.

A computer-readable storage medium having instructions stored thereon which are executable by a processor to perform a method of electronically transmitting an e-mail message from a first user having a first terminal to a second user having a second terminal, said instructions being executable by the processor to perform the steps of:

• a) electronically transmitting an e-mail message in an encrypted form together with a dynamic serial number corresponding to said message by a first terminal to a second terminal, said encrypted message being encrypted by means of a key generated by a first key generator using a seed;
• b) providing to and storing said seed in said second terminal;
• c) receiving said dynamic serial number at said second terminal and using said dynamic serial number to identify said key used to encrypt said message and a sequential order of said message;
• d) synchronising a counting value in each terminal;
• e) using said dynamic serial number, said seed and said counting value by said second terminal to independently generate said key used to encrypt said message;
• and
• f) decrypting said encrypted message at said second terminal using said independently generated key;
• g) based on said seed, generating a list of entrusted terminals;
• and
• h) accepting e-mail messages only from registries in said list.