Method and Apparatus for Ensuring Privacy in Communications Between Parties

A method of improving the privacy of parties in a communications network by hiding, in an ordered sequence of messages M[x(1), D(1)], M[x(2), D(2)], etc, communicated between a first and at least one second party sharing a key k, metadata x(i) descriptive of message processing, wherein D(i) denotes payload data, the method comprising:

• said first and said second party agreeing on a pseudo random mapping depending on a shared key k, a function Fk, mapping at least x(i) to y(i);
• said first party modifying the messages by replacing x(i) by y(i) in each message M(x(i), D(i)),
• said first party transmitting the modified messages maintaining their original order,
• on reception of a message M(y(m), D(m)), the second party using a mapping Gk to retrieve position m of received value and the original value x(m).

A method of ensuring privacy in communications between a first party and one or more second parties over a communications network, the method comprising:

• making the same pseudo-random sequence of values available to each of the first and second parties, and maintaining a mapping between the sequence or the values and a value which is used by a party receiving a message sent by the first party to handle the message or its contents;
• in messages to be sent between said first party and a second party, using a value from said sequence in place of the value to which the sequence is mapped;
• and
• at the or each receiving party, identifying the replaced value on the basis of the substituted value, and handling the message accordingly,
• wherein the value used from said sequence is changed from message to message or periodically.

A method of generating a sequence of public keys for use in securing communications between parties, the method comprising:

• providing a first public key to first and second parties;
• agreeing a shared secret between the first and second parties;
• providing the first and second parties with means for generating a sequence of further public keys using said first public key and said shared secret, such that the values of said sequence are pseudo-random in nature;
• and
• using public keys of said sequence to secure communications between the parties.