A method and system for license authentication over a network. An on-line vendor receives a digital certificate that includes a public key associated with a consumer, and a digital signature of the consumer. A license packet is generated that includes a unique serial number. A record that includes the digital certificate is stored in a memory. The license packet is optionally encrypted with the public key associated with the consumer, and the license packet is forwarded to the consumer. When a post-sale service is required, the consumer generates a request that includes the digital signature of the consumer, and the request is forwarded to the vendor. The vendor accesses the memory to authenticate that the request was sent by the consumer, and if so, the service request is fulfilled.