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The simplest of all the encryption modes is the electronic codebook mode. The message is divided into blocks and each block is encrypted separately.
ECB Encryption
ECB Decryption
ECB 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. As the encryption is deterministic, it is not CPA secure.
The speed of each encryption 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.
In this mode we have 
. The ECB is implemented by the following algorithm
Algorithm:
bitStream ecbEncrypt(bitStream m)
divide 
into 
for 
to 
do
return 
For decryption the same algorithm can be used with the decryption function 
instead of 
.
If we encrypt many blocks, partial information about the plain text is revealed. Therefor other modes are preferable.
[ This is a part of a series of post on Modes Of Encryption. I had to scribe a lecture as a requirement of a course on the Foundations Of Cryptology at the Indian Institute Of Technology. The scribe has been broken into smaller chunks so that it is easily readable. ]
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