In ECB mode (see Figure 2.2), each plaintext block is encrypted independently with the block cipher.
ci = Ek(mi) mi = Dk(ci)
Figure 2.2: Electronic Code Book mode (click for a larger image)
ECB mode is as secure as the underlying block cipher. However, plaintext patterns are not concealed. Each identical block of plaintext gives an identical block of ciphertext. The plaintext can be easily manipulated by removing, repeating, or interchanging blocks. The speed of each encryption operation is identical to that of the block cipher. ECB allows easy parallelization to yield higher performance. Unfortunately, no processing is possible before a block is seen (except for key setup).