[tsvwg] sanity checking DTLS ICMP errors

[🔓Dan Wing <[e-mail]>]

To reduce the attack surface, TCP implementations have been validating ICMP error messages to be in-window (RFC5927).

On a thread over on RTCWEB with Michael Tüxen, it seems DTLS-encrypted packets might benefit from a similar validation.  There are some fields early in the packet that might be useful for such validation,

      struct {
        ContentType type;
        ProtocolVersion version;
        uint16 epoch;                                     // New field
        uint48 sequence_number;                           // New field
        uint16 length;
        select (CipherSpec.cipher_type) {
          case block:  GenericBlockCipher;
        } fragment;
      } DTLSCiphertext;

however, both the Epoch and Sequence Number start at zero (unlike TCP's initial sequence number which has been random for nearly 20 years).  


Do we want to validate ICMP error messages for DTLS packets?  If so, can DTLS have a randomized initial sequence number?

-d