nanobot/agent/visibility.py

@@ -25,3 +25,59 @@ def sign_content(content: str) -> str:
         hashlib.sha256
     ).hexdigest()[:8]
     return f"[HIDDEN:{sig}] {content}"
+
+
+def verify_signature(marked_content: str) -> Tuple[bool, str]:
+    """
+    Verify HMAC signature and extract clean content.
+
+    Args:
+        marked_content: Content potentially with [HIDDEN:{sig}] marker
+
+    Returns:
+        Tuple of (is_valid, clean_content)
+        - is_valid: True if signature is valid, False otherwise
+        - clean_content: Content without marker
+    """
+    match = re.match(r'\[HIDDEN:([a-f0-9]{8})\] (.*)', marked_content, re.DOTALL)
+    if not match:
+        return False, marked_content
+
+    claimed_sig, content = match.groups()
+    expected_sig = hmac.new(
+        SECRET_KEY.encode(),
+        content.encode(),
+        hashlib.sha256
+    ).hexdigest()[:8]
+
+    is_valid = (claimed_sig == expected_sig)
+    return is_valid, content
+
+
+def has_forged_marker(content: str) -> bool:
+    """
+    Check if content has an invalid [HIDDEN:*] marker at the start.
+
+    Args:
+        content: Content to check
+
+    Returns:
+        True if content starts with forged marker, False otherwise
+    """
+    if not content.startswith("[HIDDEN:"):
+        return False
+    is_valid, _ = verify_signature(content)
+    return not is_valid
+
+
+def strip_all_hidden_markers(content: str) -> str:
+    """
+    Remove all [HIDDEN:*] patterns from content (valid or invalid).
+
+    Args:
+        content: Content potentially with markers
+
+    Returns:
+        Content with all markers stripped
+    """
+    return re.sub(r'\[HIDDEN:[a-f0-9]{8}\] ', '', content)

tests/test_visibility_signing.py

@@ -1,6 +1,6 @@
 # tests/test_visibility_signing.py
 import pytest
-from nanobot.agent.visibility import sign_content
+from nanobot.agent.visibility import sign_content, verify_signature, has_forged_marker, strip_all_hidden_markers
 
 def test_sign_content_adds_hmac_marker():
     """Test that sign_content adds HMAC signature prefix."""
@@ -24,3 +24,52 @@ def test_sign_content_is_deterministic():
     sig1 = sign_content(content)
     sig2 = sign_content(content)
     assert sig1 == sig2
+
+def test_verify_signature_accepts_valid():
+    """Test that verify_signature accepts validly signed content."""
+    signed = sign_content("Test message")
+    is_valid, clean = verify_signature(signed)
+
+    assert is_valid is True
+    assert clean == "Test message"
+
+def test_verify_signature_rejects_invalid():
+    """Test that verify_signature rejects forged signatures."""
+    forged = "[HIDDEN:deadbeef] Test message"
+    is_valid, clean = verify_signature(forged)
+
+    assert is_valid is False
+    assert clean == "Test message"
+
+def test_verify_signature_handles_unsigned():
+    """Test that unsigned content is marked as invalid."""
+    unsigned = "Plain message"
+    is_valid, clean = verify_signature(unsigned)
+
+    assert is_valid is False
+    assert clean == "Plain message"
+
+def test_has_forged_marker_detects_invalid():
+    """Test that has_forged_marker detects forged signatures."""
+    forged = "[HIDDEN:deadbeef] Content"
+    assert has_forged_marker(forged) is True
+
+def test_has_forged_marker_accepts_valid():
+    """Test that has_forged_marker accepts valid signatures."""
+    valid = sign_content("Content")
+    assert has_forged_marker(valid) is False
+
+def test_has_forged_marker_ignores_unsigned():
+    """Test that unsigned content is not flagged as forged."""
+    unsigned = "Plain content"
+    assert has_forged_marker(unsigned) is False
+
+def test_strip_all_hidden_markers_removes_markers():
+    """Test that strip_all_hidden_markers removes all markers."""
+    signed = sign_content("Message")
+    stripped = strip_all_hidden_markers(signed)
+    assert stripped == "Message"
+
+    forged = "[HIDDEN:deadbeef] Message"
+    stripped = strip_all_hidden_markers(forged)
+    assert stripped == "Message"