Abstract: Disclosed is a method for implementing a block cipher that includes generating an initialization vector counter. The method includes generating a key tree based on the initialization vector counter where the key tree includes one or more coeval states and where each of the one or more coeval states represents a time period where the time period of each subsequent coeval state I is nested within the previous coeval states. The key tree further includes the key that is determined for each of the one or more coeval states where each of the one or more coeval states is determined based on a counter. The message further includes encrypting, using the key, blocks of data to be transmitted where the recipient is capable of decrypting the one or more blocks only if they are received during the time period of each of the one or more coeval states.