Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
decode [ˈdiːˈkəud] vt (message) декоди́ровать (impf/perf), расшифро́вывать (расшифрова́ть perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.