Observations of some recent supernovae at a variety of wavelengths indicate that they are surrounded by dusty circumstellar envelopes. The same dust which absorbs the supernova radiation and emits infrared radiation is expected to scatter the supernova radiation. Due to the light travel time across the circumstellar envelope, the scattered radiation gives a light echo. This paper derives the scattered light curve for the single and the multiple scattering case. The theory is applied to observations of SN 1979c and SN 1980k, which did show a late infrared excess.