Java Reference
In-Depth Information
Plaintext
Ciphertext
Algorithm
Counter
000000
Plaintext
Ciphertext
Algorithm
Counter
000001
Figure 8.9
Counter mode—Block cipher mode of encryption.
8.1.5.5 Counter
he counter mode of encryption is also quite popular as a block cipher mode of encryp-
tion. he counter mode also allows block ciphers to be used as stream ciphers and perform
encryption. he counter mode is, in many ways, similar to the CFB and OFB, but in the
counter mode, there is no initialization vector used to generate a keystream to add random-
ness to the encryption process. Instead, the counter mode employs an incremental counter
for every block of data encrypted. Since the encryption of the subsequent block of data does
not depend on the ciphertext or the keystream of the previous block, like in the case of CFB
and OFB, counter mode is quite fast and the encryption of the blocks can be performed in
parallel, resulting in signiicant performance beneits. he counter mode has been depicted
in Figure 8.9.
8.1.6 Crypto Attacks
Like everything else in security, over the years cryptosystems have undergone a great deal of
attack. An encryption algorithm goes through rigorous testing over long periods of time before
it is deemed it to be adopted by the industry.
Cryptanalysis
is deined as the art and science of
obtaining the cleartext message, without having access to the key or other secret information to do
so. his is better known as codebreaking. he cryptanalyst tries to obtain the cleartext message,
either by inding laws in the encryption algorithm or by the other elements of the cryptosys-
tem like weak keys and so on. he aim of cryptography is to ensure that the work factor that an
attacker needs to break the protection that the cryptosystem has provided for the data is increased
to an infeasible level. For instance, if an attacker attempts to crack a 128-bit AES key at the rate
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