Key expansion for qkd

Abstract

A method of encrypting information using an encryption pad based on keys exchanged between quantum key distribution (QKD) stations is disclosed. The method includes establishing raw keys between two stations using QKD, processing the keys to establish a plurality of matching privacy amplified keys at each station and buffering the keys in a shared key schedule. The method also includes the option of expanding one or more of the keys in the shared key schedule using a stream cipher to create a supply of expanded keys that serve as pads for one-time-pad encryption.

1 . A method for establishing a secure key between two stations, the method comprising: 
 a) exchanging single photon signals between two quantum key distribution stations to form a plurality of raw keys at each station;    b) performing error correction and privacy amplification on the raw keys to form a plurality of privacy amplified keys at each station;    c) buffering the privacy amplified keys in each station to form matching key schedules at each station; and    d) forming at least one expanded key from a key selected from the matching key schedules, wherein the at least one expanded key is suitable for one-time pad encryption of information to be exchanged between the two stations.    
   
   
       2 . The method of  claim 1 , including: 
 a) encrypting information using the at least one expanded key as a one-time pad; and    b) transmitting the encrypted information between the two stations.    
   
   
       3 . A method of sending encrypted information between two stations, comprising: 
 a) establishing a raw key between the two stations using quantum key distribution;    b) establishing a privacy amplified key from the establish raw key;    c) providing the option of encrypting data using a one-time pad based on either the privacy amplified key as an unexpanded key, or an expanded version of the privacy amplified key as an expanded key; and    d) sending encrypted information between the two stations using a one-time pad based on either the unexpanded key or the expanded key.    
   
   
       4 . The method of  claim 3 , including: 
 a) expanding one or more of the privacy amplified keys; and    b) storing at each station the one or more expanded keys in a key schedule.    
   
   
       5 . The method of  claim 3 , including: 
 a) storing at each station one or more unexpanded keys in a first key schedule;    b) storing at each station one or more expanded keys in a second key schedule; and    c) encrypting information using one-time pads based on keys from at least one of the first and second key schedules when raw keys cannot be exchanged between the stations.