b.rs

// Cargo.toml:
// [dependencies]
// boring = { package = "superboring", version = "0.1.2" }

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Ciphertext
    let ciphertext = include_bytes!("signed_message.bin");

    // Unencrypted RSA private key in PEM format
    let rsa_pem = include_str!("sessionprivatekey.pem");

    // Import the RSA private key
    let rsa_key = boring::rsa::Rsa::private_key_from_pem(rsa_pem.as_bytes())?;

    // Decrypt the ciphertext
    let mut plaintext = vec![0; ciphertext.len()];
    let plaintext_len =
        rsa_key.private_decrypt(ciphertext, &mut plaintext, boring::rsa::Padding::PKCS1)?;
    let plaintext = &plaintext[..plaintext_len];
}