Function encrypt 

pub fn encrypt(public_key: &str, data: &[u8]) -> Result<Vec<u8>, Box<dyn Error>>

Encrypts data using a hybrid RSA + AES-GCM approach.

Takes a PEM-encoded RSA public key and plaintext data, then:

1. Generates a random AES-256 key
2. Encrypts the data with the AES key
3. Encrypts the AES key with the RSA public key
4. Returns a serialized structure containing everything needed for decryption

Arguments

• public_key - A PEM-encoded RSA public key
• data - The plaintext data to encrypt

Returns

A serialized EncryptedMessage containing the encrypted data

Errors

Returns an error if:

• The public key is invalid or cannot be parsed
• The encryption process fails
• Serialization fails