Given a result & task-id tuple $(y, t)$ with node key-pair $(k\text{priv}, k\text{pub})$ and task key-pair $(d\text{priv}, d\text{pub})$ it suffices to simply do:
$$
\begin{align}
s \gets &\text{Sign}(k\text{priv}, t || y) \
e \gets &\text{Encrypt}(d\text{pub}, y)
\end{align}
$$
The admin node will verify as follows:
$$
\begin{align}
y \gets &\text{Decrypt}(d\text{priv}, e) \
&\text{Verify}(k\text{pub}, s, t || y)
\end{align}
$$
Given a result & task-id tuple $(y, t)$ with node key-pair $(k\text{priv}, k\text{pub})$ and task key-pair $(d\text{priv}, d\text{pub})$ it suffices to simply do:
$$ \begin{align} s \gets &\text{Sign}(k\text{priv}, t || y) \ e \gets &\text{Encrypt}(d\text{pub}, y) \end{align} $$
The admin node will verify as follows:
$$ \begin{align} y \gets &\text{Decrypt}(d\text{priv}, e) \ &\text{Verify}(k\text{pub}, s, t || y) \end{align} $$