Abstract: A method for identifying a longest common substring for a string T and a string R, including selecting a registration symbol that appears in both strings R and T, constructing a first relative distance vector R′ from the appearance of the registration symbol in the string R, constructing a second relative distance vector T′ from the appearance of the registration symbol in the string T, deriving a substring pair RCS and TCS in the strings R and T respectively for each common substring pair RCS and TCS in the vectors R′ and T′ respectively, and identifying the longest matching of the RCS and TCS substring pairs as the longest common substring for the string T and the string R.