When FEMA issues an IPAWS test or alert it includes a “signature certificate.” This operates similar to a password for accessing different sites or files on a computer. In the case of a message from FEMA, a message without a correct signature the EAS device should ignore the message.
On April 26, 2021, the Required Weekly Test (RWT) from IPAWS was transmitted with an incorrect signature. The test messages had a mismatch between the digest inside the message, and the digest computed by receivers. This is a part of the validation for an alert, and checking it is required by FCC Rule 11.56(c): “EAS Participants shall configure their systems to reject all CAP-formatted EAS messages that include an invalid digital signature.”
All EAS devices should have rejected the test. The error affected all units, Gorman-Redlich, Sage Endec, DasDec and Trilithic.
On the Sage Endec, if the EAS decoder was configured correctly the message would not have been logged. DasDec and Trilithic would have logged the test but would have an error message attached. If it had been an actual alert the units would not auto forward.
1) If the alert arrived via CAP, the “signature validation” settings are probably incorrect.
2) If the alert arrived via some other CAP source, such as a CAP satellite feed, then check the settings for that CAP server.
3) If the alert arrived via an analog input, then an upstream device may be misconfigured. There are some 3rd party boxes that will receive a CAP message and output the analog legacy EAS format as audio. Some stations in some states will have that box connected to an audio input. If that box is configured to pass CAP messages with validation errors to the analog output, then it needs to be checked.
All the EAS units would have reported failed validations in a temporary log. Users should check with their device manufacture for the exact location of that file and the correct “signature validation” settings for the unit.
Stations should check and correct any issues before the next test on May 3, 2021. Stations should insert a note in the Station Log indicating the failed test and the reason for failure.