The Korea standard block cipher, SEED, is a 128-bit symmetric block cipher with a more complex F function than DES. This paper shows that SEED is vulnerable to two types of side channel attacks, a fault analysis attack and a power analysis attack. The first one is a fault insertion analysis which induces permanent faults on the whole left register of 15-round. This attack allows one to obtain the secret key by using only two faulty cipher texts for encryption and decryption processing respectively. The second attack is a more realistic differential power analysis. This attack requires about 1000 power traces to find the full secret key. The above two attacks use a reverse property of the F function to obtain secret key, where the reverse property is derived from the our research.