A computer-implemented method comprising: receiving, from a client device and by a first computing system of a plurality of multi-party computation, MPC, systems, a digital component request comprising first secret shares of data identifying user groups that include a user of the client device as a member and a set of contextual signals; transmitting (504, 314), by the first computing system, a contextual digital component request to a content platform; receiving, by the first computing system and from the content platform, selection data for a plurality of digital components, wherein the selection data comprises first vector data defining a contextual-based vector of values selected based at least in part on the set of contextual signals; obtaining, by the first computing system and for each of the plurality of digital components, second vector data defining a user group-based vector of values selected based at least in part on a respective user group corresponding to the digital component; determining, by the first computing system, a selection value for each digital component based on the first vector data and the second vector data; determining, for each digital component, a candidate parameter that indicates whether the respective user group identifier corresponding to the digital component matches a user group that includes the user as a member; generating, based on the selection values and the candidate parameters, a first secret share of a selection result that identifies, from a plurality of candidate digital components, a given digital component having a highest selection value, wherein each candidate digital component is a digital component for which the candidate parameter for the selection value corresponding to the digital component indicates that a second user group identifier corresponding to the selection value matches a user group that includes the user as a member; and transmitting, to the client device, the first secret share of a selection result identifying the given digital component, wherein determining, by the first computing system, the selection value for each digital component based on the first vector data and the second vector data comprises determining a dot product of the contextual-based vector of values for the digital component and the user group-based vector of values. receiving, from a client device and by a first computing system of a plurality of multi-party computation, MPC, systems, a digital component request comprising first secret shares of data identifying user groups that include a user of the client device as a member and a set of contextual signals; transmitting (504, 314), by the first computing system, a contextual digital component request to a content platform; receiving, by the first computing system and from the content platform, selection data for a plurality of digital components, wherein the selection data comprises first vector data defining a contextual-based vector of values selected based at least in part on the set of contextual signals; obtaining, by the first computing system and for each of the plurality of digital components, second vector data defining a user group-based vector of values selected based at least in part on a respective user group corresponding to the digital component; determining, by the first computing system, a selection value for each digital component based on the first vector data and the second vector data; determining, for each digital component, a candidate parameter that indicates whether the respective user group identifier corresponding to the digital component matches a user group that includes the user as a member; generating, based on the selection values and the candidate parameters, a first secret share of a selection result that identifies, from a plurality of candidate digital components, a given digital component having a highest selection value, wherein each candidate digital component is a digital component for which the candidate parameter for the selection value corresponding to the digital component indicates that a second user group identifier corresponding to the selection value matches a user group that includes the user as a member; and transmitting, to the client device, the first secret share of a selection result identifying the given digital component, wherein determining, by the first computing system, the selection value for each digital component based on the first vector data and the second vector data comprises determining a dot product of the contextual-based vector of values for the digital component and the user group-based vector of values.