signingKey:secp256r1
spki:secp256r1
prefix:020000
00000166d6142b50 // 1541189938000 milliseconds since the epoch
000000 // truncate tree_size
20 // 32 byte hash
  d1a0d3947db4ae8305f2ac32985957e02659b2ea3c10da52a48d2526e9af3bbc
0000 // no extensions