1. A method of implementing secure exchange of information over a communication link, comprising a method for generating a shared key, wherein the method for generating a shared key comprises the following steps: (11) establishing an infinite non-abelian group G and two subgroups A and B of G, so that for any aεA and any bεB, the equation ab=ba is true; (12) choosing, by a first communication terminal, an element g in G, wherein the first communication terminal chooses two elements b 1 , b 2 εA as private keys, and a second communication terminal chooses two elements d 1 , d 2 εB as private keys; (13) choosing, by the second communication terminal, two elements c 1 , c 2 εB, computing y=d 1 c 1 gc 2 d 2 , and sending y to the first communication terminal; (14) choosing, by the first communication terminal, four elements a 1 , a 2 , b 3 , b 4 εA, computing 
 x=b 1 a 1 ga 2 b 2 and z=b 3 a 1 ya 2 b 4 =b 3 a 1 d 1 c 1 gc 2 d 2 a 2 b 4 , and sending (x, z) to the second communication terminal; (15) choosing, by the second communication terminal, two elements d 3 , d 4 εB, computing 
 w=d 3 c 1 xc 2 d 4 =d 3 c 1 b 1 a 1 ga 2 b 2 c 2 d 4 
 and 
 v=d 1 −1 zd 2 −1 =d 1 −1 b 3 a 1 d 1 c 1 gc 2 d 2 a 2 b 4 d 2 −1 =b 3 a 1 c 1 gc 2 a 2 b 4 and sending (w, v) to the first communication terminal; (16) computing, by the first communication terminal, 
 u=b 1 −1 wb 2 −1 =b 1 −1 d 3 c 1 b 1 a 1 ga 2 b 2 c 2 d 4 b 2 −1 =d 3 c 1 a 1 ga 2 c 2 d 4 , and sending u to the second communication terminal; and (17) computing, by the first communication terminal, K A =b 3 −1 vb 4 −1 =a 1 c 1 gc 2 a 2 , and computing, by the second communication terminal, K B =d 3 −1 ud 4 −1 =c 1 a 1 ga 2 c 2 ; because a 1 , a 2 εA, and c 1 , c 2 εB, a 1 and c 1 are separately commute with a 2 and c 2 in multiplication, so that the first communication terminal and the second communication terminal reach a shared key K=K A =K B ; exchanging information over the communication link between the first communication terminal and the second communication terminal based on the shared key.