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Expand the common DKIM selector probe list #12

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36 changes: 33 additions & 3 deletions src/sentineldeck/scanners/email_security.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,12 +16,42 @@

# Best-effort DKIM selector probes. Absence is inconclusive, so DKIM findings
# are always reported with indeterminate confidence.
# Only static, publicly documented selectors. Skip per-tenant tokens
# (Amazon SES, Postmark dates, HubSpot hs1-<id>, etc.).
COMMON_DKIM_SELECTORS = (
"default", "google", "selector1", "selector2", "k1", "k2",
"mail", "dkim", "s1", "s2", "mandrill", "zoho", "protonmail", "fm1",
"default", # generic / self-hosted
"mail", # generic / Brevo legacy
"mail2", # Brevo / Sendinblue rotation pair
"dkim", # generic / self-hosted
"google", # Google Workspace
"google2", # Google Workspace key rotation
"selector1", # Microsoft 365
"selector2", # Microsoft 365 key rotation
"k1", # Mailchimp
"k2", # Mailchimp
"k3", # Mailchimp
"mte1", # Mailchimp Transactional
"mte2", # Mailchimp Transactional
"mandrill", # legacy Mailchimp Transactional
"s1", # SendGrid
"s2", # SendGrid
"zoho", # Zoho Mail
"zmail", # Zoho Mail common default
"protonmail", # Proton Mail
"protonmail2", # Proton Mail key rotation
"protonmail3", # Proton Mail key rotation
"fm1", # Fastmail
"fm2", # Fastmail
"fm3", # Fastmail
"sig1", # Apple iCloud custom domain
"s1024", # legacy Yahoo / AOL
"s2048", # legacy Yahoo / AOL
"zendesk1", # Zendesk
"zendesk2", # Zendesk
"brevo1", # Brevo
"brevo2", # Brevo
)


def extract_spf_policy(record: str | None) -> str | None:
if not record:
return None
Expand Down
6 changes: 6 additions & 0 deletions tests/test_email_security.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
from sentineldeck.risk.scoring import build_findings
from sentineldeck.scanners.dns_lookup import parse_mx_records, parse_txt_records
from sentineldeck.scanners.email_security import (
COMMON_DKIM_SELECTORS,
analyze_email_security,
count_spf_lookups,
dkim_key_bits,
Expand Down Expand Up @@ -203,3 +204,8 @@ def test_email_findings_are_indeterminate_when_dns_errors():

assert findings["spf-missing"].confidence == "indeterminate"
assert findings["dmarc-missing"].confidence == "indeterminate"

def test_common_dkim_selectors_are_unique_and_include_documented_providers():
assert len(COMMON_DKIM_SELECTORS) == len(set(COMMON_DKIM_SELECTORS))
for name in ("k3", "mte1", "protonmail2", "fm3", "sig1", "zendesk1", "google2"):
assert name in COMMON_DKIM_SELECTORS