The easiest mode of operation is the ECB mode which is a direct application of the DES algorithm. In ECB encryption, the forward cipher function is applied directly and independently to each block of the plaintext. The resulting sequence of output blocks is the ciphertext. In ECB decryption, the inverse cipher function is applied directly and independently to each block of the ciphertext. The resulting sequence of output blocks is the plaintext. As shown on this slide, for ECB encryption plaintext corresponds to the input block, ciphertext to the output block. As described, the flow is the opposite for the ECB decryption.