Data Update between two Excel worksheets

This project requires an external app that either by itself or as a macro in one of the spreadsheets. The two spreadsheets are "Input" and "Master." The project requires that the program go through the "Input" sheet, row by row, capture the "key" column and two other columns of data. Then it is to go over to the "Master" sheet, find the "key" column and update that row with the other two columns of data. This program will run from top to bottom through the "Input" spreadsheet and process all the rows. The "Input" spreadsheet will change every week so this program / macro will run weekly to update the "Master" spreadsheet.