O <em>Major Tallmadge did not trust anyone with his codes other than Woodhull, Townsend, and General Washington.</em>
Explanation:
<em>The statement best expresses the central idea of the excerpt due to the fact that he has the ability to develop more machines (secret writing system) which he invented but choose to invent only four.</em>
<em>He sent to the above named people whom he trusted while he retained one of the secret writing system to himself.</em>
