Block cipher is an encryption algorithm that takes a fixed size of input say b bits and produces a ciphertext of b bits again. If the input is larger than b bits it can be divided further. For different applications and uses, there are several modes of operations for a block cipher. It is easier because of direct encryption of each block of input plaintext and output is in form of blocks of encrypted ciphertext. Generally, if a message is larger than b bits in size, it can be broken down into a bunch of blocks and the procedure is repeated.
Attention reader! Procedure of ECB is illustrated below:. Advantages of using ECB — Parallel encryption of blocks of bits is possible, thus it is a faster way of encryption. News and Special Offers occasional. Techopedia Explains Cipher Block Chaining CBC Invented in , cipher block chaining provides a consistent way to encrypt and decrypt large amounts of data. Related Question How does machine learning support better supply chain management?
Share this Term. Related Terms Encryption Cipher. Initialization Vector. Tech moves fast! Stay ahead of the curve with Techopedia! In this regard, the way of working of the block cipher becomes similar to the way of working of a typical stream cipher. Because of the continuous creation of keystream bits, both encryption and decryption can be performed using only one thread at a time. Similarly, as in the CFB mode, both data encryption and decryption uses the same cipher encryption algorithm.
If one bit of a plaintext or ciphertext message is damaged for example because of a transmission error , only one corresponding ciphertext or respectively plaintext bit is damaged as well. It is possible to use various correction algorithms to restore the previous value of damaged parts of the received message. The biggest drawback of OFB is that the repetition of encrypting the initialization vector may produce the same state that has occurred before.
It is an unlikely situation but in such a case the plaintext will start to be encrypted by the same data as previously. Using the CTR mode makes block cipher way of working similar to a stream cipher.
As in the OFB mode, keystream bits are created regardless of content of encrypting data blocks. In this mode, subsequent values of an increasing counter are added to a nonce value the nonce means a number that is unique: number used once and the results are encrypted as usual. The nonce plays the same role as initialization vectors in the previous modes. It is one of the most popular block ciphers modes of operation.
Both encryption and decryption can be performed using many threads at the same time. If one bit of a plaintext or ciphertext message is damaged, only one corresponding output bit is damaged as well.
Thus, it is possible to use various correction algorithms to restore the previous value of damaged parts of received messages. As in the case of the CBC mode, one should change the secret key after using it for encrypting a number of sent messages. It can be proved that the CTR mode generally provides quite good security and that the secret key needs to be changed less often than in the CBC mode.
For example, for the AES cipher the secret key should be changed after about 2 64 plaintext blocks. Crypto-IT There is nothing concealed that will not be disclosed. Encryption in the ECB mode. Decryption in the ECB mode. The bitmap image encrypted using DES and the same secret key. A block cipher processes the data blocks of fixed size.
Usually, the size of a message is larger than the block size. Hence, the long message is divided into a series of sequential message blocks, and the cipher operates on these blocks one at a time.
This mode is a most straightforward way of processing a series of sequentially listed message blocks. The user takes the first block of plaintext and encrypts it with the key to produce the first block of ciphertext. He then takes the second block of plaintext and follows the same process with same key and so on so forth.
The ECB mode is deterministic , that is, if plaintext block P1, P2,…, Pm are encrypted twice under the same key, the output ciphertext blocks will be the same. In fact, for a given key technically we can create a codebook of ciphertexts for all possible plaintext blocks.
Encryption would then entail only looking up for required plaintext and select the corresponding ciphertext. In reality, any application data usually have partial information which can be guessed.
For example, the range of salary can be guessed. A ciphertext from ECB can allow an attacker to guess the plaintext by trial-and-error if the plaintext message is within predictable.
For example, if a ciphertext from the ECB mode is known to encrypt a salary figure, then a small number of trials will allow an attacker to recover the figure. In general, we do not wish to use a deterministic cipher, and hence the ECB mode should not be used in most applications. CBC mode of operation provides message dependence for generating ciphertext and makes the system non-deterministic. The operation of CBC mode is depicted in the following illustration.
Feed ciphertext block into top register and continue the operation till all plaintext blocks are processed.
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