Cryptography Questions Medium
The Electronic Codebook with Output Feedback (ECB-OFB) mode is a hybrid encryption mode that combines the Electronic Codebook (ECB) mode and the Output Feedback (OFB) mode.
In ECB-OFB mode, the plaintext is divided into blocks of fixed size, typically 64 or 128 bits. Each block is then encrypted independently using a symmetric encryption algorithm, such as AES (Advanced Encryption Standard), with a unique encryption key. This is similar to how ECB mode works.
However, instead of directly using the encrypted blocks as the ciphertext, ECB-OFB mode applies the Output Feedback (OFB) mode to generate a keystream. The keystream is then XORed with the plaintext blocks to produce the ciphertext.
The OFB mode operates by using a feedback mechanism, where the previous ciphertext block is encrypted using the same encryption key to generate the next keystream block. This keystream is then XORed with the plaintext block to produce the ciphertext block.
The advantage of using ECB-OFB mode is that it provides confidentiality and allows for parallel encryption and decryption of blocks. Each block can be encrypted or decrypted independently, which can be advantageous in certain scenarios. However, it does not provide integrity or authenticity of the message, as it does not include any form of message authentication.
It is important to note that ECB-OFB mode should not be used for encrypting large amounts of data, as it is vulnerable to certain attacks, such as block repetition and chosen plaintext attacks. It is generally recommended to use more secure modes, such as Cipher Block Chaining (CBC) or Galois/Counter Mode (GCM), which provide both confidentiality and integrity.