Cryptography Tutorials - Herong's Tutorial Examples - Version 5.33, by Dr. Herong Yang
What is ECB (Electronic CodeBook) Operation Mode?
This section describes what is ECB (Electronic CodeBook) Operation Mode - each plaintext block is encrypted independently without any input from other blocks.
ECB (Electronic CodeBook) is the simplest operation mode comparing to other operation modes. It can be described by the formula and the diagram below with notations defined earlier:
C[i] = Ek(P[i]) P--| P--| P--| | | | Ek() Ek() Ek() | | | C C C
As you can see from the formula and the diagram, in ECB mode, each ciphertext block is obtained by applying the DES encryption process to the current plaintext block directly. So the current ciphertext block has not dependency on any previous plaintext blocks.
The disadvantage of ECB mode is that identical plaintext blocks are encrypted to identical ciphertext blocks; thus, it does not hide data patterns well. In some senses it doesn't provide message confidentiality at all, and it is not recommended for cryptographic protocols.
wikipedia has a striking example of the degree to which ECB can reveal patterns in the plaintext. The example uses a bitmap file of an image as the plaintext message. After applying DES encryption in ECB mode, the ciphertext message can be viewed as a new bitmap image file. The new image does reveal major patterns of the original image very clearly.
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