[feat] SCTP checksum compute

microschc/protocol/__init__.py

@@ -6,13 +6,15 @@
 from .ipv4 import IPv4ComputeFunctions, IPv4Fields
 from .ipv6 import IPv6ComputeFunctions, IPv6Fields
 from .udp import UDPComputeFunctions, UDPFields
+from .sctp import SCTPComputeFunctions, SCTPFields
 
 ComputeFunctions: Dict[str, Tuple[ComputeFunctionType, ComputeFunctionDependenciesType]] = {
     IPv4Fields.TOTAL_LENGTH: IPv4ComputeFunctions[IPv4Fields.TOTAL_LENGTH],
     IPv4Fields.HEADER_CHECKSUM: IPv4ComputeFunctions[IPv4Fields.HEADER_CHECKSUM],
     IPv6Fields.PAYLOAD_LENGTH: IPv6ComputeFunctions[IPv6Fields.PAYLOAD_LENGTH],
     UDPFields.LENGTH: UDPComputeFunctions[UDPFields.LENGTH],
-    UDPFields.CHECKSUM: UDPComputeFunctions[UDPFields.CHECKSUM]
+    UDPFields.CHECKSUM: UDPComputeFunctions[UDPFields.CHECKSUM],
+    SCTPFields.CHECKSUM: SCTPComputeFunctions[SCTPFields.CHECKSUM]
 }
 
 

microschc/protocol/sctp.py

@@ -8,15 +8,18 @@
 
 
 from enum import Enum
+from functools import reduce
 
+from microschc.crypto.crc import CRC32C_TABLE, crc32c
 from microschc.protocol.registry import PARSERS, REGISTER_PARSER, ProtocolsIDs
 
 SCTP_HEADER_ID = 'SCTP'
 
 from enum import Enum
 from typing import Dict, List, Tuple, Type
-from microschc.binary.buffer import Buffer
+from microschc.binary.buffer import Buffer, Padding
 from microschc.parser import HeaderParser, ParserError
+from microschc.protocol.compute import ComputeFunctionDependenciesType, ComputeFunctionType
 from microschc.rfc8724 import FieldDescriptor, HeaderDescriptor
 
 SCTP_HEADER_ID = 'SCTP'
@@ -604,9 +607,9 @@ def _parse_parameter(self, buffer: Buffer) -> Tuple[List[FieldDescriptor], int]:
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |        Parameter Type         |       Parameter Length        |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-        \                                                               \
+        \                                                               \ 
         /                        Parameter Value                        /
-        \                                                               \
+        \                                                               \ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         """
         fields: List[FieldDescriptor] = []
@@ -632,4 +635,26 @@ def _parse_parameter(self, buffer: Buffer) -> Tuple[List[FieldDescriptor], int]:
             )
         return fields, parameter_length_value + parameter_padding_length
 
+
+def _compute_checksum(decompressed_fields: List[Tuple[str, Buffer]], rule_field_position: int) -> Buffer:
+    """
+    Checksum algorithm is the Castagnoli CRC32C Checksum Algorithm (CRC32c).
+    """
+    fields_values: List[Buffer] = [field_value for _, field_value in decompressed_fields]
+
+    sctp_checksum_position: int = rule_field_position
+    #   - SCTP checksum is the 4th field of UDP
+    sctp_header_and_payload_fields: List[Buffer] = [field for field in fields_values[sctp_checksum_position-3:]]
+    sctp_header_and_payload: Buffer = reduce(lambda x, y: x+y, sctp_header_and_payload_fields)
+
+    crc_init: int = 0xffffffff    
+    checksum = crc32c(buffer=sctp_header_and_payload, crc_init=crc_init)  
+    checksum = ~checksum
+    checksum_buffer = reduce(lambda x,y : x+y, list(checksum.chunks(length=8))[::-1])
+    return checksum_buffer
+
+SCTPComputeFunctions: Dict[str, Tuple[ComputeFunctionType, ComputeFunctionDependenciesType]] = {
+    SCTPFields.CHECKSUM: (_compute_checksum, { f.value for f in SCTPFields if f is not SCTPFields.CHECKSUM })
+}
+
 REGISTER_PARSER(protocol_id=ProtocolsIDs.SCTP, parser_class=SCTPParser)

tests/protocol/test_sctp.py

@@ -1,5 +1,5 @@
 from typing import Dict, List, Tuple
-from microschc.protocol.sctp import SCTPParser, SCTPFields
+from microschc.protocol.sctp import SCTPParser, SCTPFields, SCTPComputeFunctions
 from microschc.parser.parser import HeaderDescriptor
 from microschc.rfc8724 import FieldDescriptor
 from microschc.binary.buffer import Buffer
@@ -1104,4 +1104,23 @@ def test_sctp_parser_parse_cookie_ack():
     chunk_length_fd:FieldDescriptor = sctp_header_descriptor.fields[6]
     assert chunk_length_fd.id == SCTPFields.CHUNK_LENGTH
     assert chunk_length_fd.position == 0
-    assert chunk_length_fd.value == Buffer(content=b'\x00\x04', length=16)
+    assert chunk_length_fd.value == Buffer(content=b'\x00\x04', length=16)
+
+def test_sctp_compute_checksum():
+
+    partially_reconstructed_content: bytes = bytes(
+        b'\x00\x07\x00\x07\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x20'
+        b'\x43\x23\x25\x44\x00\x00\xff\xff\x00\x11\x00\x11\x5c\xfe\x37\x9f'
+        b'\xc0\x00\x00\x04\x00\x0c\x00\x06\x00\x05\x00\x00'
+
+    )
+    expected_checksum: Buffer = Buffer(content=b'\x37\x61\xa7\x46', length=32)
+    parser:SCTPParser = SCTPParser()
+
+    partially_reconstructed_packet: Buffer = Buffer(content=partially_reconstructed_content, length=len(partially_reconstructed_content)*8)
+    sctp_header_descriptor: HeaderDescriptor = parser.parse(buffer=partially_reconstructed_packet)
+
+
+    decompressed_fields: List[Tuple[str, Buffer]] = [ (field.id,field.value) for field in sctp_header_descriptor.fields]
+    checksum_buffer: Buffer = SCTPComputeFunctions[SCTPFields.CHECKSUM][0](decompressed_fields, 3)
+    assert checksum_buffer == expected_checksum