21 CFR §1311.50

1. (a)The recipient of a digitally signed order must do the following before filling the order:
   1. (1)Verify the integrity of the signature and the order by having the system validate the order.
   2. (2)Verify that the certificate holder's CSOS digital certificate has not expired by checking the expiration date against the date the order was signed.
   3. (3)Check the validity of the certificate holder's certificate by checking the Certificate Revocation List.
   4. (4)Check the certificate extension data to determine whether the sender has the authority to order the controlled substance.
2. (b)A recipient may cache Certificate Revocation Lists for use until they expire.