class Net::SSH::Authentication::Agent

def blob_for_add(priv_key)
  # Ideally we'd have something like `to_private_blob` on the various key types, but the
  # nuances with encoding (e.g. `n` and `e` are reversed for RSA keys) make this impractical.
  case priv_key.ssh_type
  when /^ssh-dss$/
    Net::SSH::Buffer.from(:bignum, priv_key.p, :bignum, priv_key.q, :bignum, priv_key.g,
                          :bignum, priv_key.pub_key, :bignum, priv_key.priv_key).to_s
  when /^ssh-dss-cert-v01@openssh\.com$/
    Net::SSH::Buffer.from(:string, priv_key.to_blob, :bignum, priv_key.key.priv_key).to_s
  when /^ecdsa\-sha2\-(\w*)$/
    curve_name = OpenSSL::PKey::EC::CurveNameAliasInv[priv_key.group.curve_name]
    Net::SSH::Buffer.from(:string, curve_name, :mstring, priv_key.public_key.to_bn.to_s(2),
                          :bignum, priv_key.private_key).to_s
  when /^ecdsa\-sha2\-(\w*)-cert-v01@openssh\.com$/
    Net::SSH::Buffer.from(:string, priv_key.to_blob, :bignum, priv_key.key.private_key).to_s
  when /^ssh-ed25519$/
    Net::SSH::Buffer.from(:string, priv_key.public_key.verify_key.to_bytes,
                          :string, priv_key.sign_key.keypair).to_s
  when /^ssh-ed25519-cert-v01@openssh\.com$/
    # Unlike the other certificate types, the public key is included after the certifiate.
    Net::SSH::Buffer.from(:string, priv_key.to_blob,
                          :string, priv_key.key.public_key.verify_key.to_bytes,
                          :string, priv_key.key.sign_key.keypair).to_s
  when /^ssh-rsa$/
    # `n` and `e` are reversed compared to the ordering in `OpenSSL::PKey::RSA#to_blob`.
    Net::SSH::Buffer.from(:bignum, priv_key.n, :bignum, priv_key.e, :bignum, priv_key.d,
                          :bignum, priv_key.iqmp, :bignum, priv_key.p, :bignum, priv_key.q).to_s
  when /^ssh-rsa-cert-v01@openssh\.com$/
    Net::SSH::Buffer.from(:string, priv_key.to_blob, :bignum, priv_key.key.d,
                          :bignum, priv_key.key.iqmp, :bignum, priv_key.key.p,
                          :bignum, priv_key.key.q).to_s
  end
end