Patent ID: 7492903

Claim:
A secret key distribution method of distributing two random number tables correlated to each other serving as a secret key between sites A and B between which an N number of relay stations R(i) (i=1, 2, . . . , N) are located, the secret key distribution method comprising: generating an N+1 number of photon pairs PP(j) (j=1, 2, . . . , N+1) consisting of photons P 1 (j) and photons P 2 (j) connected through entanglement; sending a photon P 1 ( 1 ) of the photon pair PP( 1 ) to A and a photon P 2 ( 1 ) of the photon pair PP( 1 ) to R( 1 ), a photon P 1 (k) of the photon pair PP(k) to R(k−1) and a photon P 2 (k) of the photon pair PP(k) to R(k) (k=2, 3, . . . , N), and a photon P 1 (N+1) of the photon pair PP(N+1) to R(N) and a photon P 2 (N+1) of the photon pair PP(N+1) to B; determining a base for detecting a photon by exchanging information between A and R( 1 ), between R(m) and R(m+1) (m=1, 2, . . . , N−1), and between R(N) and B, after the individual photons reach A, R(i) and B, detecting photons connected through entanglement between A and R( 1 ), between R(m) and R(m+1), and between R(N) and B by using the same base, respectively, acquiring a bit corresponding to the detected value of each photon depending on a predetermined correspondence, and setting the bit acquired by the detection of the photon P 1 ( 1 ) in A to be B(P 1 ( 1 )), the bit acquired by the detection of the photon P 2 (i) in R(i) to be B(P 2 (i)), the bit acquired by the detection of the photon P 1 (i+1) to be B(P 1 (i+1)), and the bit acquired by the detection of the photon P 2 (N+1) in B to be B(P 2 (N+1)); causing R( 1 ) to send to R( 2 ) information C( 1 ) as to whether to invert B(P 2 ( 2 )) depending on B(P 2 ( 1 )) and B(P 1 ( 2 )), and causing R( 2 ) to set B(P 2 ( 2 )) to B(P 2 ( 2 ))′ depending on C( 1 ); causing R(m) to send to R(m+1) information C(m) as to whether to invert B(P 2 (m+1)) depending on B(P 2 (m))′ and B(P 1 (m+1)), and causing R(m+1) to set B(P 2 (m+1)) to B(P 2 (m+1))′ depending on C(m), the operations are performed with respect to m=2, 3, . . . , N−1 in that order; causing R(N) to send to B information C(N) as to whether to invert B(P 2 (N+1)) depending on B(P 2 (N))′ and B(P 1 (N+1)), and causing B to set B(P 2 (N+1)) to B(P 2 (N+1))′ depending on C(N) so as to correlate the bit B(P 1 ( 1 )) acquired in A to the bit B(P 2 (N+1))′ acquired in B; and repeating procedures for acquiring bits correlated between A and B by the above operations as many times as necessary, and setting B(P 1 ( 1 )) and B(P 2 (N+1))′ acquired in a q-th procedure to be a q-th bit of the random number tables acquired in A and in B, respectively.