diff --git a/testing/requirements.txt b/testing/requirements.txt
index e0e1a6ff..3db8695e 100644
--- a/testing/requirements.txt
+++ b/testing/requirements.txt
@@ -23,3 +23,5 @@ git+https://github.com/coinkite/bsms-bitcoin-secure-multisig-setup.git@master#eg
 # BBQr library
 git+https://github.com/coinkite/BBQr.git@master#egg=bbqr&subdirectory=python
 
+# for backend testing
+requests==2.32.3
diff --git a/testing/test_ccc.py b/testing/test_ccc.py
new file mode 100644
index 00000000..678ef30f
--- /dev/null
+++ b/testing/test_ccc.py
@@ -0,0 +1,121 @@
+# (c) Copyright 2024 by Coinkite Inc. This file is covered by license found in COPYING-CC.
+#
+# tests related to CCC feature
+#
+#
+import pytest, requests, re, time, random
+from binascii import a2b_hex, b2a_hex
+from base64 import urlsafe_b64encode
+from urllib.parse import urlparse, parse_qs
+from onetimepass import get_totp
+from helpers import prandom
+
+# TODO: we will rotate the server key before release.
+SERVER_PUBKEY = '036d0f95c3aaf5cd3e8be561b07814fbb1c9ee2171ed301828151975411472a2fd'
+
+def make_session_key(his_pubkey=None):
+    # - second call: given the pubkey of far side, calculate the shared pt on curve
+    # - creates session key based on that
+    from ecdsa.curves import SECP256k1
+    from ecdsa import VerifyingKey, SigningKey
+    from ecdsa.util import number_to_string
+    from hashlib import sha256
+
+    my_key = SigningKey.generate(curve=SECP256k1, hashfunc=sha256)
+
+    his_pubkey = VerifyingKey.from_string(bytes.fromhex(SERVER_PUBKEY),
+                                                curve=SECP256k1, hashfunc=sha256)
+
+    # do the D-H thing
+    pt = my_key.privkey.secret_multiplier * his_pubkey.pubkey.point
+
+    # final key is sha256 of that point, serialized (64 bytes).
+    order = SECP256k1.order
+    kk = number_to_string(pt.x(), order) + number_to_string(pt.y(), order)
+
+    return sha256(kk).digest(), my_key.get_verifying_key().to_string('compressed')
+
+
+@pytest.fixture
+def make_2fa_url():
+    def doit(shared_secret=b'A'*16, nonce='12345678',
+                wallet='Example wallet name', is_q=0, prod=True, encrypted=False):
+
+        base = 'http://127.0.0.1:5070/2fa?' if not prod else 'https://coldcard.com/2fa?'
+
+        assert is_q in {0, 1}
+        assert len(shared_secret) == 16     # base32
+        assert isinstance(nonce, str)       # hex digits or 8 dec digits in Mk4 mode
+
+        from urllib.parse import quote
+
+        qs = f'ss={shared_secret}&q={is_q}&g={nonce}&nm={quote(wallet)}'
+
+        print(f'2fa URL: {qs}')
+
+        if not encrypted:
+            return base + qs
+
+        # pick eph key
+        ses_key, pubkey = make_session_key()
+
+        import pyaes
+        enc = pyaes.AESModeOfOperationCTR(ses_key, pyaes.Counter(0)).encrypt
+
+        qs = urlsafe_b64encode(pubkey + enc(qs.encode('ascii')))
+
+        return base + qs.decode('ascii')
+
+    return doit
+
+@pytest.fixture
+def roundtrip_2fa():
+    def doit(url, shared_secret, local=False):
+        if local:
+            url = url.replace('https://coldcard.com/', 'http://127.0.0.1:5070/')
+
+        if int(time.time() % 30) > 29:
+            # avoid end of time period
+            time.sleep(3)
+
+        answer = '%06d' % get_totp(shared_secret)
+        assert len(answer) == 6
+
+        resp = requests.post(url, data=dict(answer=answer))
+
+        # server HTML will have this line in response for our use
+        #   <!--TESTING CCC-AUTH:00000FFF -->
+
+        if '<!--TESTING' not in resp.text:
+            raise RuntimeError("server did not accept code")
+
+        ans = re.search('<!--TESTING (\S*)', resp.text).group(1)
+
+        #print(f'Got answer: {ans}')
+
+        return ans
+
+        
+    return doit
+
+@pytest.mark.parametrize('shared_secret', [ '6SPAJXWD3XJTUQWO', 'TU3QZ7VFMTJCPSS6' ])
+@pytest.mark.parametrize('q_mode', [ True, False] )
+@pytest.mark.parametrize('enc', [ True] )
+def test_2fa_server(shared_secret, q_mode, make_2fa_url, enc, roundtrip_2fa):
+
+    nonce = prandom(32).hex() if q_mode else str(random.randint(1000_0000, 9999_9999))
+
+    # TODO command line flag to select local coldcard.com or production version
+
+    url = make_2fa_url(shared_secret, nonce, is_q=int(q_mode), encrypted=enc, prod=True)
+
+    #print(url)
+
+    ans = roundtrip_2fa(url, shared_secret)
+
+    assert ans == f'CCC-AUTH:{nonce}'.upper() if q_mode else nonce
+
+    # NOTE: cannot re-start same test until next 30-second period because of rate limiting
+    # check on server side.
+
+# EOF