Block cipher modes of operation (ECB, CBC, GCM) A block cipher is a cryptographic algorithm that processes data in blocks of a fixed size. These bloc...
A block cipher is a cryptographic algorithm that processes data in blocks of a fixed size. These blocks are typically 128 bits long, but they can be of different sizes depending on the cipher.
Three commonly used block cipher modes of operation are:
1. Electronic Codebook (ECB)
ECB is the simplest and most basic mode of operation.
Each block is treated independently, with no notion of order or relative positions of the blocks within the plaintext.
ECB is vulnerable to chosen-plaintext attacks, where an attacker can specify the plaintext to be encrypted and obtain the encrypted version.
Example: ECB is used for storing key schedules in unencrypted files, such as in DES (Data Encryption Standard).
2. Counter (CBC)
CBC is a more secure mode of operation than ECB.
It takes an initial salt value and iterates through the plaintext, constructing the ciphertext block by block.
This process prevents an attacker from predicting the next block based on the previous blocks.
CBC is more secure against chosen-plaintext attacks but can be vulnerable to a known-plaintext attack if the salt is leaked.
Example: CBC is commonly used for encrypting network protocols like HTTPS and TLS.
3. Galois-Hadamard Mode (GCM)
GCM is the most secure of the three modes and is recommended for applications where maximum security is paramount.
GCM uses a Galois-Hadamard code, a family of linear codes that are difficult to break.
GCM is resistant to all known attacks and is considered the safest mode of operation for block ciphers.
Example: GCM is used for encrypting sensitive data in electronic transactions and financial transactions