Function decrypt 

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

Decrypts data that was encrypted with the hybrid RSA + AES-GCM approach.

Takes a PEM-encoded RSA private key and encrypted data, then:

1. Deserializes the encrypted message structure
2. Decrypts the AES key using the RSA private key
3. Uses the decrypted AES key to decrypt the actual data

Arguments

• private_key - A PEM-encoded RSA private key
• data - The encrypted data to decrypt (as serialized by encrypt)

Returns

The decrypted plaintext data

Errors

Returns an error if:

• The private key is invalid or cannot be parsed
• The encrypted data cannot be deserialized
• The RSA decryption of the AES key fails
• The AES decryption of the data fails