A method for measuring trust in a transaction over a public key certificate network includes associating each edge KA→KB of an public key certificate network connecting two public keys KA and KB with a probability p that information about KB is reliable, and a confidence c that is a total dollar amount of transactions which have involved using edge KA→KB. One or more authentication paths are formed in the public key certificate network starting from public key KS and ending with a target public key KT. A limit l of an amount of insurance that an owner of KS is willing to provide to a user interested in a transaction with an owner of KT is calculated, and for each amount m