ARIA is a 128-bit symmetric block cipher having 128-bit, 192-bit, or 256-bit key lengths. The cipher is a substitution-permutation encryption network (SPN) that uses an involutional binary matrix. This paper shows that a careless implementation of ARIA on smartcards is vulnerable to a differential power analysis attack. This attack is realistic because we can measure power consumption signals at two kinds of S-boxes and two types of substitution layers. By analyzing the power traces, we can find all round keys and also extract a master key from only two round keys using circular rotation, XOR, and involutional operations for two types of layers.