Mode of Operation

About

In asymmetric encryption, such as RSA, the concept of "block size" is different from symmetric encryption algorithms like AES. Here's how block size works in the context of asymmetric encryption and how it handles data that exceeds the block size:

Asymmetric Encryption and Block Size:

• Asymmetric encryption algorithms like RSA do not operate on fixed-size blocks of plaintext data like symmetric block ciphers (e.g., AES).

• RSA encrypts data in smaller chunks than its key size. For example, with a 2048-bit RSA key, you can encrypt data in chunks that are less than 2048 bits.

• There isn't a direct "block size" in RSA encryption in the same sense as AES. RSA encryption directly applies modular exponentiation to encrypt data that is less than the key size.

Handling Data Larger than RSA Key Size:

• If the plaintext data is larger than the RSA key size, it must be segmented into smaller chunks that can individually undergo RSA encryption.

• Typically, RSA encryption is used to encrypt symmetric keys or small amounts of data due to its computational overhead and size limitations.

Padding Schemes:

• Padding schemes like PKCS1Padding or OAEP (Optimal Asymmetric Encryption Padding) are used to ensure that the plaintext can be properly encrypted and decrypted without loss of information or security vulnerabilities.

• These padding schemes add additional bytes to the plaintext before encryption to ensure that it fits within the constraints of the RSA encryption process.

Encryption Process:

• When encrypting data larger than the key size, the data is split into smaller blocks that fit the RSA constraints (less than the key size).

• Each block is padded to ensure it conforms to the padding scheme requirements.

• RSA encryption is then applied to each padded block individually.

Decryption Process:

• During decryption, RSA decrypts each encrypted block individually.

• The padding scheme is used to validate and remove the padding from each decrypted block to reconstruct the original plaintext.

Performance Considerations:

• Due to the computational overhead of RSA encryption and decryption, it is typically used to encrypt smaller pieces of data or symmetric keys.

• For encrypting larger amounts of data, a hybrid encryption approach is often used where RSA encrypts a symmetric key, and then the symmetric key encrypts the actual data.

We might see like this "RSA/ECB/PKCS1Padding"

The mode of operation "ECB" doesn't mean anything in this context, it should have been"NONE" or it should have been left out completely.