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fix(test): ServerHello oracle — dead carry gate + stub skip-as-pass (audit F10)#79

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Merged
JC-000 merged 1 commit into from
Aug 13, 2026
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fix(test): ServerHello oracle — dead carry gate + stub skip-as-pass (audit F10) #79

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74 changes: 49 additions & 25 deletions tools/test_tls_handshake.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,6 @@

from c64_test_harness import (
Labels,
ViceConfig,
ViceInstanceManager,
read_bytes,
write_bytes,
Expand All@@ -34,6 +33,8 @@
wait_for_text,
)

from _vice_helpers import default_vice_config

# ---------------------------------------------------------------------------
# Constants
# ---------------------------------------------------------------------------
Expand DownExpand Up@@ -207,6 +208,33 @@ def check_labels(labels, names):
return True


# A routine that is still `clc; rts` is unimplemented: it reports success
# without doing anything.
STUB_CLC_RTS = bytes([0x18, 0x60])


def report_if_stub(transport, addr, name):
"""Announce (loudly) that *name* is a ``clc; rts`` stub.

Returns True when the routine at *addr* is a stub.

Callers must NOT skip on a stub. This file used to answer a detected
stub with ``return 0, 0``, which dropped the whole group out of both
the passed and failed counters -- the suite then reported success
while testing nothing, and the stub (a routine that claims success
unconditionally) sailed through. A stub has to FAIL its group's
tests: the diagnostic below explains why they fail, and the tests
still run so the failures land in the denominator (audit finding
F10, same shape as F3).
"""
if read_bytes(transport, addr, 2) == STUB_CLC_RTS:
print(f"\n STUB: {name} is a `clc; rts` stub -- unimplemented. "
"The tests below still run and are expected to FAIL; a stub "
"is never a skip and never a pass.")
return True
return False


# ---------------------------------------------------------------------------
# C64 helper functions
# ---------------------------------------------------------------------------
Expand DownExpand Up@@ -598,6 +626,10 @@ def test_server_hello_parse(transport, labels, rng):
hs_buf = labels["tls_rec_buf"]
hs_len_addr = labels["tls_rec_len"]

# A stub is reported, not skipped -- all three tests below then run and
# fail on their own merits.
report_if_stub(transport, parse_sh, "tls_parse_server_hello")

# --- Test 3a: Valid ServerHello with x25519 ---
print("\n [3a] ServerHello: valid parse (x25519, cipher 0x1303)")
server_random = bytes(rng.getrandbits(8) for _ in range(32))
Expand All@@ -619,12 +651,15 @@ def test_server_hello_parse(transport, labels, rng):
[len(hs_msg) & 0xFF, (len(hs_msg) >> 8) & 0xFF])

try:
regs = jsr(transport, parse_sh, timeout=120.0)

# Check carry flag (C=0 means success)
carry = 0
if regs and "P" in regs:
carry = regs["P"] & 0x01
# Read the carry through the jsr_check_carry trampoline (LDA #0 /
# ROL A / STA), which captures C on the 6502 itself. The previous
# code read it out of the harness register dict under the key "P";
# VICE's binary monitor names the status register "FL", so the
# lookup never matched, `carry` stayed pinned at 0, and the error
# branch below was unreachable (audit finding F10, same root cause
# as F1 in test_tls_record.py). The trampoline has no dependency
# on register naming at all.
carry = jsr_check_carry(transport, parse_sh, timeout=120.0)

if carry == 0:
# Verify server_random was extracted
Expand All@@ -649,24 +684,12 @@ def test_server_hello_parse(transport, labels, rng):
print(f" expected: {server_pubkey[:8].hex()}...")
print(f" got: {got_pubkey[:8].hex()}...")
else:
# Parser returned error but it might be a stub
# Check if the implementation is a stub (just clc; rts)
code = read_bytes(transport, parse_sh, 2)
if code == bytes([0x18, 0x60]): # CLC; RTS
print(" SKIP: tls_parse_server_hello is a stub (clc; rts)")
return 0, 0
failed += 1
print(" FAIL: parser returned C=1 (error) for valid ServerHello")
except Exception as e:
failed += 1
print(f" FAIL: {e}")

# Check if this is a stub before running error tests
code = read_bytes(transport, parse_sh, 3)
if code[:2] == bytes([0x18, 0x60]): # CLC; RTS
print(" SKIP: remaining ServerHello tests (stub implementation)")
return 0, 0

# --- Test 3b: Wrong cipher suite -> C=1 ---
print(" [3b] ServerHello: wrong cipher suite -> error")
sh_body_bad_cipher = build_server_hello(
Expand DownExpand Up@@ -871,11 +894,9 @@ def test_key_schedule(transport, labels):

derive_hs = labels["tls_derive_handshake_keys"]

# Check if this is a stub (clc; rts)
code = read_bytes(transport, derive_hs, 2)
if code == bytes([0x18, 0x60]):
print("\n SKIP: tls_derive_handshake_keys is a stub (clc; rts)")
return 0, 0
# Same rule as the ServerHello group: a stub is reported, not skipped.
# The five tests below then fail against the RFC 8448 vectors.
report_if_stub(transport, derive_hs, "tls_derive_handshake_keys")

# Set up inputs: shared secret and transcript hash
write_bytes(transport, labels["tls_shared_secret"], SHARED_SECRET)
Expand DownExpand Up@@ -1264,7 +1285,10 @@ def main():
f"{found_optional}/{len(optional_labels)} optional TLS labels found")

# Launch VICE
config = ViceConfig(prg_path=PRG_PATH, warp=True, ntsc=True, sound=False)
# default_vice_config() applies the mandatory -reu/-reusize=512 flags;
# see tools/_vice_helpers.py for the rationale.
config = default_vice_config(prg_path=PRG_PATH, warp=True, ntsc=True,
sound=False)
print(f"\n=== Starting VICE ===")

with ViceInstanceManager(config=config) as mgr:
Expand Down