Multiple-site private network secured by IPsec using blockchain network for key exchange

In some implementations, a method includes: preparing, at a first networking device, an incoming security key update request transaction, the incoming security key update request transaction including a request by the first networking device to use an incoming security key for incoming communications with other networking devices during an IPsec session, where the first networking device and the other networking devices communicate over a blockchain network including a blockchain; transmitting the incoming security key update request transaction from the first networking device to the blockchain network for validation; updating a copy of the blockchain with a block, the block including a validation of the incoming security key update request transaction that was transmitted to the blockchain network; and using at least the updated blockchain to update an IPsec security association (SA) or an IPsec security policy (SP) used by the first networking device.