The invention introduces an apparatus for detecting errors during data encryption. The apparatus includes a search circuitry and a substitution check circuitry. The key generation circuitry is arranged operably to convert a first value of one byte corresponding to a plaintext, an intermediate encryption result, or a round key into a second value of a K-bit according to an 8-to-K lookup table, where K is an integer ranging from 10 to 15 and the second value comprises (K minus 8) bits of a Hamming parity. The substitution check circuitry is arranged operably to employ check formulae corresponding to the 8-to-K lookup table to determine whether an error is occurred during a conversion of the first value of the one byte into the second value of the K-bit, and output an error signal when finding the error, where a total amount of the formulae is K minus 8.