This is a comprehensive study of multiplicative codes of Reed-Muller type and their applications.Our codes apply to theelds of cryptography and coding theory, especially to multiparty computa-tion and secret sharing schemes. We also study the AB method to analyze the minimum distanceof linear codes. The multiplicative codes of Reed-Muller type and the AB method are connectedwhen we study the distance and dual distance of a code and its square. Generator matrices for ourcodes use a combination of blocks, where a block consists of all columns of a given weight. Severalinteresting linear codes, which are best known linear codes for a given length and dimension, canbe constructed in this way.i