Integrity services supported by a PKI use cryptographic techniques to allow parties needing to maintain the integrity of their data transmissions to assure receiving parties that the data they receive is the data that was intended and that it was sent from whom it was intended. In practice, like the data cryptography in confidentiality services (see Confidentiality), a PKI generally supports symmetric-key cryptographic mechanisms that assure data integrity "under the covers" in a communications environment that is authenticated using public-key cryptography. This data integrity service typically makes itself known only when data is found to have been unexpectedly altered, requiring input from the data consumer in order to handle the corrupted data.