DNS: add the DAU, DHU and N3U EDNS(0) options

These options are used for signaling cryptographic algorithm
understanding in DNS Security Extensions (DNSSEC):
https://www.rfc-editor.org/rfc/rfc6975.html

The patch was cross-checked with Wireshark:
```sh
>>> dau = EDNS0DAU(alg_code=['RSA/SHA-256', 'RSA/SHA-512'])
>>> dhu = EDNS0DHU(alg_code=['SHA-1', 'SHA-256', 'SHA-384'])
>>> n3u = EDNS0N3U(alg_code=['SHA-1'])
>>> tdecode(Ether()/IP()/UDP()/DNS(ar=[DNSRROPT(rdata=[dau, dhu, n3u])]))
...
            Option: DAU - DNSSEC Algorithm Understood (RFC6975)
                Option Code: DAU - DNSSEC Algorithm Understood (RFC6975) (5)
                Option Length: 2
                Option Data: 080a
                DAU: RSA/SHA-256 (8)
                DAU: RSA/SHA-512 (10)
            Option: DHU - DS Hash Understood (RFC6975)
                Option Code: DHU - DS Hash Understood (RFC6975) (6)
                Option Length: 3
                Option Data: 010204
                DHU: SHA-1 (1)
                DHU: SHA-256 (2)
                DHU: SHA-384 (4)
            Option: N3U - NSEC3 Hash Understood (RFC6975)
                Option Code: N3U - NSEC3 Hash Understood (RFC6975) (7)
                Option Length: 1
                Option Data: 01
                N3U: SHA-1 (1)
```

scapy/layers/dns.py

@@ -34,6 +34,7 @@
     ConditionalField,
     Field,
     FieldLenField,
+    FieldListField,
     FlagsField,
     I,
     IP6Field,
@@ -89,6 +90,22 @@
 dnsclasses = {1: 'IN', 2: 'CS', 3: 'CH', 4: 'HS', 255: 'ANY'}
 
 
+# 09/2013 from http://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml  # noqa: E501
+dnssecalgotypes = {0: "Reserved", 1: "RSA/MD5", 2: "Diffie-Hellman", 3: "DSA/SHA-1",  # noqa: E501
+                   4: "Reserved", 5: "RSA/SHA-1", 6: "DSA-NSEC3-SHA1",
+                   7: "RSASHA1-NSEC3-SHA1", 8: "RSA/SHA-256", 9: "Reserved",
+                   10: "RSA/SHA-512", 11: "Reserved", 12: "GOST R 34.10-2001",
+                   13: "ECDSA Curve P-256 with SHA-256", 14: "ECDSA Curve P-384 with SHA-384",  # noqa: E501
+                   252: "Reserved for Indirect Keys", 253: "Private algorithms - domain name",  # noqa: E501
+                   254: "Private algorithms - OID", 255: "Reserved"}
+
+# 09/2013 from http://www.iana.org/assignments/ds-rr-types/ds-rr-types.xhtml
+dnssecdigesttypes = {0: "Reserved", 1: "SHA-1", 2: "SHA-256", 3: "GOST R 34.11-94", 4: "SHA-384"}  # noqa: E501
+
+# 12/2023 from https://www.iana.org/assignments/dnssec-nsec3-parameters/dnssec-nsec3-parameters.xhtml  # noqa: E501
+dnssecnsec3algotypes = {0: "Reserved", 1: "SHA-1"}
+
+
 def dns_get_str(s, full=None, _ignore_compression=False):
     """This function decompresses a string s, starting
     from the given pointer.
@@ -387,21 +404,25 @@ def i2m(self, pkt, s):
 # RFC 2671 - Extension Mechanisms for DNS (EDNS0)
 
 edns0types = {0: "Reserved", 1: "LLQ", 2: "UL", 3: "NSID", 4: "Reserved",
-              5: "PING", 8: "edns-client-subnet", 10: "COOKIE",
+              5: "DAU", 6: "DHU", 7: "N3U", 8: "edns-client-subnet", 10: "COOKIE",
               15: "Extended DNS Error"}
 
 
-class EDNS0TLV(Packet):
+class _EDNS0Dummy(Packet):
+    name = "Dummy class that implements extract_padding()"
+
+    def extract_padding(self, p):
+        # type: (bytes) -> Tuple[bytes, Optional[bytes]]
+        return "", p
+
+
+class EDNS0TLV(_EDNS0Dummy):
     name = "DNS EDNS0 TLV"
     fields_desc = [ShortEnumField("optcode", 0, edns0types),
                    FieldLenField("optlen", None, "optdata", fmt="H"),
                    StrLenField("optdata", "",
                                length_from=lambda pkt: pkt.optlen)]
 
-    def extract_padding(self, p):
-        # type: (bytes) -> Tuple[bytes, Optional[bytes]]
-        return "", p
-
     @classmethod
     def dispatch_hook(cls, _pkt=None, *args, **kargs):
         # type: (Optional[bytes], *Any, **Any) -> Type[Packet]
@@ -410,11 +431,7 @@ def dispatch_hook(cls, _pkt=None, *args, **kargs):
         if len(_pkt) < 2:
             return Raw
         edns0type = struct.unpack("!H", _pkt[:2])[0]
-        if edns0type == 8:
-            return EDNS0ClientSubnet
-        if edns0type == 15:
-            return EDNS0ExtendedDNSError
-        return EDNS0TLV
+        return EDNS0OPT_DISPATCHER.get(edns0type, EDNS0TLV)
 
 
 class DNSRROPT(Packet):
@@ -432,6 +449,36 @@ class DNSRROPT(Packet):
                                    length_from=lambda pkt: pkt.rdlen)]
 
 
+# RFC 6975 - Signaling Cryptographic Algorithm Understanding in
+# DNS Security Extensions (DNSSEC)
+
+class EDNS0DAU(_EDNS0Dummy):
+    name = "DNSSEC Algorithm Understood (DAU)"
+    fields_desc = [ShortEnumField("optcode", 5, edns0types),
+                   FieldLenField("optlen", None, count_of="alg_code", fmt="H"),
+                   FieldListField("alg_code", None,
+                                  ByteEnumField("", 0, dnssecalgotypes),
+                                  count_from=lambda pkt:pkt.optlen)]
+
+
+class EDNS0DHU(_EDNS0Dummy):
+    name = "DS Hash Understood (DHU)"
+    fields_desc = [ShortEnumField("optcode", 6, edns0types),
+                   FieldLenField("optlen", None, count_of="alg_code", fmt="H"),
+                   FieldListField("alg_code", None,
+                                  ByteEnumField("", 0, dnssecdigesttypes),
+                                  count_from=lambda pkt:pkt.optlen)]
+
+
+class EDNS0N3U(_EDNS0Dummy):
+    name = "NSEC3 Hash Understood (N3U)"
+    fields_desc = [ShortEnumField("optcode", 7, edns0types),
+                   FieldLenField("optlen", None, count_of="alg_code", fmt="H"),
+                   FieldListField("alg_code", None,
+                                  ByteEnumField("", 0, dnssecnsec3algotypes),
+                                  count_from=lambda pkt:pkt.optlen)]
+
+
 # RFC 7871 - Client Subnet in DNS Queries
 
 class ClientSubnetv4(StrLenField):
@@ -489,7 +536,7 @@ class ClientSubnetv6(ClientSubnetv4):
     af_default = b"\x20"  # 2000::
 
 
-class EDNS0ClientSubnet(Packet):
+class EDNS0ClientSubnet(_EDNS0Dummy):
     name = "DNS EDNS0 Client Subnet"
     fields_desc = [ShortEnumField("optcode", 8, edns0types),
                    FieldLenField("optlen", None, "address", fmt="H",
@@ -510,9 +557,6 @@ class EDNS0ClientSubnet(Packet):
                        ClientSubnetv4("address", "192.168.0.0",
                                       length_from=lambda p: p.source_plen))]
 
-    def extract_padding(self, p):
-        return "", p
-
 
 # RFC 8914 - Extended DNS Errors
 
@@ -552,7 +596,7 @@ def extract_padding(self, p):
 
 
 # https://www.rfc-editor.org/rfc/rfc8914.html
-class EDNS0ExtendedDNSError(Packet):
+class EDNS0ExtendedDNSError(_EDNS0Dummy):
     name = "DNS EDNS0 Extended DNS Error"
     fields_desc = [ShortEnumField("optcode", 15, edns0types),
                    FieldLenField("optlen", None, length_of="extra_text", fmt="!H",
@@ -561,25 +605,17 @@ class EDNS0ExtendedDNSError(Packet):
                    StrLenField("extra_text", "",
                                length_from=lambda pkt: pkt.optlen - 2)]
 
-    def extract_padding(self, p):
-        return "", p
-
-
-# RFC 4034 - Resource Records for the DNS Security Extensions
-
 
-# 09/2013 from http://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml  # noqa: E501
-dnssecalgotypes = {0: "Reserved", 1: "RSA/MD5", 2: "Diffie-Hellman", 3: "DSA/SHA-1",  # noqa: E501
-                   4: "Reserved", 5: "RSA/SHA-1", 6: "DSA-NSEC3-SHA1",
-                   7: "RSASHA1-NSEC3-SHA1", 8: "RSA/SHA-256", 9: "Reserved",
-                   10: "RSA/SHA-512", 11: "Reserved", 12: "GOST R 34.10-2001",
-                   13: "ECDSA Curve P-256 with SHA-256", 14: "ECDSA Curve P-384 with SHA-384",  # noqa: E501
-                   252: "Reserved for Indirect Keys", 253: "Private algorithms - domain name",  # noqa: E501
-                   254: "Private algorithms - OID", 255: "Reserved"}
+EDNS0OPT_DISPATCHER = {
+    5: EDNS0DAU,
+    6: EDNS0DHU,
+    7: EDNS0N3U,
+    8: EDNS0ClientSubnet,
+    15: EDNS0ExtendedDNSError,
+}
 
-# 09/2013 from http://www.iana.org/assignments/ds-rr-types/ds-rr-types.xhtml
-dnssecdigesttypes = {0: "Reserved", 1: "SHA-1", 2: "SHA-256", 3: "GOST R 34.11-94", 4: "SHA-384"}  # noqa: E501
 
+# RFC 4034 - Resource Records for the DNS Security Extensions
 
 def bitmap2RRlist(bitmap):
     """

test/scapy/layers/dns_edns0.uts

@@ -78,6 +78,63 @@ def _test():
 retry_test(_test)
 
 
++ EDNS0 - DAU
+
+= Basic instantiation & dissection
+
+b = b'\x00\x05\x00\x00'
+
+p = EDNS0DAU()
+assert raw(p) == b
+
+p = EDNS0DAU(b)
+assert p.optcode == 5 and p.optlen == 0 and p.alg_code == []
+
+b = raw(EDNS0DAU(alg_code=['RSA/SHA-256', 'RSA/SHA-512']))
+
+p = EDNS0DAU(b)
+repr(p)
+assert p.optcode == 5 and p.optlen == 2 and p.alg_code == [8, 10]
+
+
++ EDNS0 - DHU
+
+= Basic instantiation & dissection
+
+b = b'\x00\x06\x00\x00'
+
+p = EDNS0DHU()
+assert raw(p) == b
+
+p = EDNS0DHU(b)
+assert p.optcode == 6 and p.optlen == 0 and p.alg_code == []
+
+b = raw(EDNS0DHU(alg_code=['SHA-1', 'SHA-256', 'SHA-384']))
+
+p = EDNS0DHU(b)
+repr(p)
+assert p.optcode == 6 and p.optlen == 3 and p.alg_code == [1, 2, 4]
+
+
++ EDNS0 - N3U
+
+= Basic instantiation & dissection
+
+b = b'\x00\x07\x00\x00'
+
+p = EDNS0N3U()
+assert raw(p) == b
+
+p = EDNS0N3U(b)
+assert p.optcode == 7 and p.optlen == 0 and p.alg_code == []
+
+b = raw(EDNS0N3U(alg_code=['SHA-1']))
+
+p = EDNS0N3U(b)
+repr(p)
+assert p.optcode == 7 and p.optlen == 1 and p.alg_code == [1]
+
+
 + EDNS0 - Client Subnet
 
 = Basic instantiation & dissection
@@ -123,3 +180,8 @@ assert p.info_code == 6 and p.optlen == 45 and p.extra_text == b'proof of non-ex
 p = DNSRROPT(raw(DNSRROPT(rdata=[EDNS0ExtendedDNSError(), EDNS0ClientSubnet(), EDNS0TLV()])))
 assert len(p.rdata) == 3
 assert all(Raw not in opt for opt in p.rdata)
+
+for opt_class in EDNS0OPT_DISPATCHER.values():
+    p = DNSRROPT(raw(DNSRROPT(rdata=[EDNS0TLV(), opt_class(), opt_class()])))
+    assert len(p.rdata) == 3
+    assert all(Raw not in opt for opt in p.rdata)