1 files changed, 79 insertions, 0 deletions
diff --git a/crafted-pkt/tls-handshake-fragments.py b/crafted-pkt/tls-handshake-fragments.py
new file mode 100755
index 0000000..2883933
--- /dev/null
+++ b/crafted-pkt/tls-handshake-fragments.py
@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+import argparse
+import random
+
+from scapy.all import *
+
+# msg_type: 1 (Client Hello)
+# length: 47
+#   client_version: 1.2
+#   random: 32 bytes
+#   session_id: empty
+#   cipher_suite[1]: 0x002F (TLS_RSA_WITH_AES_128_CBC_SHA)
+#   compression_method[1]: null
+#   extensions[1]: 0xAAAA (GREASE) with two values (will be used as identifier)
+clientHelloMsg = bytes([
+    0x01,
+    0x00, 0x00, 0x31,
+    0x03, 0x03,
+]) + 32 * b'3' + bytes([
+    0x00,
+    0x00, 0x02, 0x00, 0x2f,
+    0x01, 0x00,
+    0x00, 0x06, 0xaa, 0xaa, 0x00, 0x02,
+    0x00, 0x00
+])
+assert len(clientHelloMsg) == 53
+clientHelloMsgBase = clientHelloMsg[:-2]
+
+def CH(num : int):
+    '''Returns a Client Hello message with some identifier.'''
+    return clientHelloMsgBase + num.to_bytes(2, 'big')
+
+def TLSRecord(data):
+    # Handshake (22), TLSv1.0
+    return b'\x16\x03\x01' + len(data).to_bytes(2, 'big') + data
+
+parser = argparse.ArgumentParser()
+parser.add_argument('--seed', type=int)
+parser.add_argument('--count', type=int, default=256, help='Streams count')
+parser.add_argument('output_file')
+args = parser.parse_args()
+
+if args.seed is not None:
+    random.seed(args.seed)
+
+# Pick a number of messages per stream such that at least the case is triggered
+# where a record contains the end of a message, a full message and the start of
+# another message. A lot more than three per record will likely not be useful
+# since it does not trigger reassembly.
+hsPerStream = 10
+maxRecordSize = len(clientHelloMsg) * 4
+
+# Fragment handshake message over TLS records,
+# fragment TLS records over TCP segments.
+packets = []
+for i in range(args.count):
+    hs = b''.join(CH(hsPerStream * i + j + 1) for j in range(hsPerStream))
+    seq = 0x1000
+    while hs:
+        # Does not matter that n > maxRecordSize, it is capped anyway.
+        n = random.randint(1, maxRecordSize)
+        recordData, hs = hs[:n], hs[n:]
+        seg = TLSRecord(recordData)
+        pkt = IP()/TCP(flags='A', seq=seq, sport=0xc000 + i, dport=443)/seg
+        packets.append(pkt)
+        seq += len(seg)
+
+wrpcap(args.output_file, packets)
+
+r"""
+Test:
+
+    tshark -r hs-frag.pcapng -Tfields -Y tls.handshake.extension.data -e tls.handshake.extension.data | tr , '\n'
+
+Expected result: for a given 'count' streams, expect hexadecimal numbers 0001 up
+to and including 10*count. E.g. for --count=10 the output should match:
+
+    printf '%004x\n' {1..100}
+"""