Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for analyzing content item compliance with specified guidelines. In one aspect, a method includes receiving training data that specify manual classifications of content items and feature values for each of the content items, where each manual classification specifies whether the content item is a violating content item. Using the training data, a compliance model is trained to classify an unclassified content item as a violating content item based on the feature values of the unclassified content item. A determination is made that the compliance model has an accuracy measure that meets a threshold accuracy measure. In response to determining that the accuracy measure for the compliance model meets the accuracy threshold, unclassified content items are classified using the feature values for the unclassified content items, and data specifying the classifications are provided.

Abstract: A method of verifying electronic payments generated using a key unknown to the verifier. In anticipation of accepting electronic payments, a seller requests and receives from a bank a conversation key and a first set of electronic verifiers for a first set of electronic payments from a customer. Each verifier allows authentication of an associated electronic payment without revealing the private key used by the customer to generate the electronic payments. Prior to initiating a transaction or series of transactions, the customer requests payment information from the seller for use, along with the master key, in generating electronic payments Afterward, when the customer pays with an electronic payment, the seller authenticates the electronic payment using one of the verifiers. The seller responds to the buyer's request if the electronic payment is authenticated.

Abstract: A method of space efficient electronic payments. A customer initiates an electronic transaction by transmitting a request for payment information to a seller. In response, the customer receives from the seller the payment information needed to generate an electronic payment. The customer determines the reliability of the payment information by authenticating it. If the payment information is authenticated, then the customer generates an electronic payment using the payment information and a master key unknown to the seller. Finally, the customer transmits the electronic payment to the seller along with a request for desired goods and/or services.

Abstract: A method of redeeming for a seller electronic payments generated by and received from a customer using a master key unknown to the seller. In anticipation of making electronic payments, a customer sends a bank the master key that he will use to generate electronic payments. The bank stores the master key. Later, the bank receives from the seller a redemption request including a seller identifier, a first value of a payment index, and an electronic payment associated with the first value of the payment index. The bank authenticates the electronic payment by comparing the electronic payment to a hash of a string including the master key, the seller identifier, and the first value of the payment index. If the electronic payment is authenticated, the bank determines an amount due to the seller and credits that amount to the seller.