Cal. Rev. & Tax. Code § 218.5
In order to assure the accuracy of the state's reimbursements for the homeowners' property tax exemption and to prevent duplications of the exemptions within the state and improper overlapping with other benefits provided by law, county assessors shall supply information from homeowners' property tax exemption claims and county records as is specified by written request of the board, and with the concurrence of the Controller, necessary to fully identify all homeowners' property tax exemption claims allowed by the assessors. The board may specify that the information include all or a part of the names and social security numbers of claimants and spouses and the identity and location of the dwelling to which the exemption applies. The information may be required in the form of data processing media or other media and in such format as is compatible with the recordkeeping processes of the counties and the auditing procedures of the state.
Ca. Rev. and Tax. Code § 218.5