5.1 Security Considerations for Implementers

As specified in sections 2.2.3, 2.2.4, and 3, information such as whether the message is a request or a response, and which message version, is present in both the DRS Protocol Extensions for SMTP headers and inside the serialized DRS message. The fields in the DRS Protocol Extensions for SMTP headers are sent without encryption or authentication, and they are subject to potential snooping and tampering. The implementation must consider that all header fields are potentially not valid until verified; in particular, the values of cbDataOffset and cbExtOffset have to be validated to fall within the extent of the PayloadData. The implementation must ensure that buffer under-run, buffer over-run, or integer arithmetic overflow do not occur during decoding and subsequent processing of the frame.<24>

When data is encrypted, the key length that is used is determined by the length of the public key in the recipient's certificate. The Domain Controller Replication certificate has a public key length of 56-bits and the Domain Controller Email certificate has a public key length of 128 bits.<25>