More Information about RSA OAEP Padding for Encryption

Optimal Asymmetric Encryption Padding (OAEP) is a padding scheme used in RSA encryption to provide additional security by introducing randomness and structure to the plaintext before encryption.

Key Features of OAEP Padding

1. Randomness:
   • Incorporates a randomly generated seed to ensure the same plaintext encrypts to different ciphertexts each time, enhancing security.
2. Two-step Masking:
   • Uses a Mask Generation Function (MGF) to generate masks for the plaintext and the seed, creating a padded message resistant to certain attacks.
3. Probabilistic Nature:
   • Prevents deterministic relationships between plaintext and ciphertext.

OAEP Structure

The padded message consists of:

1. A randomly generated seed.
2. A masked data block containing the plaintext.
3. A process using MGF to derive masks for both the seed and the data block.

Optional Parameters

1. Mask Generation Function (MGF):
   • A hash-based function used to generate a mask for the seed and the data block.
   • Commonly MGF1, which is based on a hash function (e.g., SHA-1 or SHA-256).
   • Purpose: Ensures secure and random masking of input values.
2. Label (L):
   • An optional, user-defined string included during the padding process.
   • Defaults to an empty string if not provided.
   • Purpose: Provides additional context or binding to the encryption process.
   • The hash of the label is embedded in the padded message, so if the same label is not provided during decryption, it will fail.

Example Parameters in Practice

• Hash Function: Determines the security properties of the padding.
  • Example: SHA-256.
• Label: Provides application-specific binding.
  • Example: “transaction-id-12345”.

Summary

• OAEP Padding is a secure RSA encryption padding scheme that uses a combination of randomness and masking for security.
• The MGF ensures robust randomness, while the label is an optional context string that adds flexibility to the encryption process.