A secure cryptographic network is established among operational units in a system. A public key cryptosystem is initially used to establish secure communication links. Then, each secure communication link will be provided with a unique private encryption key from a private key cryptosystem. Every operational unit in the system will comprise a secure chip integrated circuit. These secure chips will comprise a programmable processor and a read-only memory. A plurality of personalization stations are used to provide each secure chip with a public/private encryption or signature key pair. The secure chips will execute a program from the read-only memory on the secure chips to verify that the public/private key pair has been received from an authorized source. Each secure chip will also be provided with a chain of authentication certificates originating from a trusted authority. The public signature key of the trusted authority will be programmed into the read-only memory of the secure chip, for reliable access to this information. When establishing a secure communication link between two operational units, each of the operational units will authenticate the other operational unit by verifying the content and source of each of the authentication certificates in the respective chains.