A key distribution service operated by a signature authority distributes one-time-use cryptographic keys to one or more delegates that generate digital signatures on behalf of the signature authority. The key distribution service uses a root seed value to generate subordinate seeds. The subordinate seeds are used to generate a set of cryptographic keys. Hashes are generated for each key, and the hashes are arranged into a Merkle tree with a root hash controlled by the signature authority. In response to a request from a delegate, the signature authority provides a subordinate seed to the delegate. The delegate uses the subordinate seed to generate one or more cryptographic keys. The cryptographic keys are used to generate digital signatures which are verifiable up to the root hash of the Merkle tree. Additional subordinate seeds may be distributed to entities by the signature authority when appropriate.