Rsa Encrypt Decrypt

RSA encryption allows anyone to encrypt a message using the recipient's Public Key. However, only the recipient, holding the mathematically linked Private Key, can decrypt and read the message.

Raw ("textbook") RSA is deterministic and highly vulnerable to chosen-ciphertext attacks. To fix this, padding schemes introduce randomness before encryption.

• PKCS#1 v1.5: An older padding scheme. It is vulnerable to Bleichenbacher's oracle attacks and is no longer recommended.
• OAEP (Optimal Asymmetric Encryption Padding): The modern standard. It uses a hash function (like SHA-256) and a mask generation function (MGF1) to securely scramble the plaintext before RSA mathematical operations.

A common misconception is that RSA can encrypt files. RSA cannot encrypt data larger than its key size (minus padding overhead). For a 2048-bit key using OAEP with SHA-256, the maximum payload is just 190 bytes!

Real-world usage: Instead of encrypting the actual file with RSA, systems use Hybrid Encryption. They generate a random symmetric key (like AES-256), encrypt the large file rapidly with AES, and then use RSA to encrypt only the AES key.

const encrypted = await crypto.subtle.encrypt(
  {
    name: "RSA-OAEP" // Required modern padding
  },
  publicKey,
  encodedData
);