Service-Tokens/attacks_test.py at main · leepi/Service-Tokens · GitHub

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"""
attacks_test.py  --  prove every threat-model finding is closed.

authorize() returns (ok, claims, reason): ok at [0], reason at [2].
Run: python3 attacks_test.py
"""

import time
from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey

import pop_crypto as pc
from stores import InMemoryAtomicStore, TokenBucketRateLimiter
from pop_server import AuthServer, Client, ResourceServer, RequestContext

AUD = "https://api.example.com"
URL = "https://api.example.com/orders"
M = "GET"
passed = 0


def check(name, cond):
    global passed
    print("  [%s] %s" % ("PASS" if cond else "FAIL", name))
    assert cond, name
    passed += 1


def fleet():
    auth = AuthServer(issuer="https://auth.example.com")
    replay = InMemoryAtomicStore()
    nonces = InMemoryAtomicStore()
    revoc = auth.revocations
    rs_a = ResourceServer(auth.jwks(), auth.issuer, AUD, replay, nonces, revoc)
    rs_b = ResourceServer(auth.jwks(), auth.issuer, AUD, replay, nonces, revoc)
    return auth, rs_a, rs_b


def ctx(method=M, url=URL, channel=None):
    return RequestContext(method, url, channel_value=channel)


print("baseline + H1 (cross-replica replay blocked by shared atomic store)")
auth, rs_a, rs_b = fleet()
alice = Client()
tok, jti, exp = auth.issue_bound_token("alice", alice.jwk(AUD), AUD)
proof = alice.make_proof(M, URL, tok, AUD)
check("legit request on replica A allowed", rs_a.authorize(tok, proof, ctx())[0])
check("H1: SAME proof replayed on replica B denied",
      rs_b.authorize(tok, proof, ctx())[2] == "proof_replayed")

print("H1 (revocation propagates across replicas)")
auth, rs_a, rs_b = fleet()
tok, jti, exp = auth.issue_bound_token("alice", alice.jwk(AUD), AUD)
auth.revoke(jti, ttl=300)
check("revoked token denied on replica B",
      rs_b.authorize(tok, alice.make_proof(M, URL, tok, AUD), ctx())[2]
      == "token_revoked")

print("H2 (no bearer fallback: downgraded/unbound token rejected)")
auth, rs_a, _ = fleet()
kid, sk = auth.keys.signer()
now = int(time.time())
unbound = pc.jws_sign({"alg": "EdDSA", "typ": "JWT", "kid": kid},
                      {"iss": auth.issuer, "aud": AUD, "sub": "alice",
                       "iat": now, "nbf": now, "exp": now + 300, "jti": "x"}, sk)
check("H2: token lacking cnf/pop rejected",
      rs_a.authorize(unbound, alice.make_proof(M, URL, unbound, AUD), ctx())[2]
      == "token_not_sender_constrained")

print("H3 (server derives htu from trusted request; client value ignored)")
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("alice", alice.jwk(AUD), AUD)
hdr = {"alg": "EdDSA", "typ": "pop+jwt", "jwk": alice.jwk(AUD)}
lying = pc.jws_sign(hdr, {"htm": M, "htu": "https://api.example.com/admin",
                          "iat": now, "jti": "j1",
                          "ath": pc.b64u(pc.sha256(tok.encode()))},
                    alice._key(AUD))
check("H3: client-controlled htu can't redirect the binding",
      rs_a.authorize(tok, lying, ctx(url=URL))[2] == "uri_mismatch")
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("alice", alice.jwk(AUD), AUD)
check("H3: query string is canonicalized away (same resource)",
      rs_a.authorize(tok, alice.make_proof(M, URL + "?page=2", tok, AUD),
                     ctx(url=URL + "?page=2"))[0])

print("M1 (channel binding for high-value tokens)")
chan = b"tls-exporter-or-client-cert-der"
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD, require_channel=True)
check("M1: missing channel binding denied",
      rs_a.authorize(tok, alice.make_proof(M, URL, tok, AUD),
                     ctx(channel=chan))[2] == "channel_binding_mismatch")
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD, require_channel=True)
check("M1: no channel presented at all denied",
      rs_a.authorize(tok, alice.make_proof(M, URL, tok, AUD), ctx())[2]
      == "channel_binding_required")
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD, require_channel=True)
check("M1: correct channel binding allowed",
      rs_a.authorize(tok, alice.make_proof(M, URL, tok, AUD, channel_value=chan),
                     ctx(channel=chan))[0])
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD, require_channel=True)
check("M1: wrong channel value denied",
      rs_a.authorize(tok, alice.make_proof(M, URL, tok, AUD, channel_value=b"evil"),
                     ctx(channel=chan))[2] == "channel_binding_mismatch")

print("M2 (key rotation with overlap; unknown kid rejected)")
auth, _, _ = fleet()
tok_old, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD)
auth.keys.rotate()
tok_new, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD)
rs = ResourceServer(auth.jwks(), auth.issuer, AUD, InMemoryAtomicStore(),
                    InMemoryAtomicStore(), auth.revocations)
check("M2: pre-rotation token still validates (overlap)",
      rs.authorize(tok_old, alice.make_proof(M, URL, tok_old, AUD), ctx())[0])
check("M2: new-key token validates",
      rs.authorize(tok_new, alice.make_proof(M, URL, tok_new, AUD), ctx())[0])

print("M3 (claim confidentiality via nested encryption)")
auth, _, _ = fleet()
rs_priv = X25519PrivateKey.generate()
enc_tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD,
                                       encrypt_to_x25519_pub=rs_priv.public_key())
check("M3: token is opaque/encrypted on the wire", pc.is_encrypted(enc_tok))
rs = ResourceServer(auth.jwks(), auth.issuer, AUD, InMemoryAtomicStore(),
                    InMemoryAtomicStore(), auth.revocations, decryption_key=rs_priv)
check("M3: RS decrypts then authorizes",
      rs.authorize(enc_tok, alice.make_proof(M, URL, enc_tok, AUD), ctx())[0])
tampered = enc_tok[:-2] + ("AA" if enc_tok[-2:] != "AA" else "BB")
check("M3: tampered ciphertext rejected",
      rs.authorize(tampered, alice.make_proof(M, URL, tampered, AUD), ctx())[2]
      == "decryption_failed")

print("L1 (per-audience keys distinct -> reduced linkability)")
check("L1: different audience -> different PoP key",
      alice.jwk(AUD)["x"] != alice.jwk("https://other.example.com")["x"])

print("L4 (issuer is checked)")
auth, _, _ = fleet()
wrong = ResourceServer(auth.jwks(), "https://evil.example.com", AUD,
                       InMemoryAtomicStore(), InMemoryAtomicStore(), auth.revocations)
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD)
check("L4: unexpected issuer denied",
      wrong.authorize(tok, alice.make_proof(M, URL, tok, AUD), ctx())[2]
      == "wrong_issuer")

print("L6 (alg allowlist: forged 'none' rejected)")
auth, rs_a, _ = fleet()
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD)
none_proof = pc.b64u(b'{"alg":"none","typ":"pop+jwt","jwk":{}}') + "." + \
    pc.b64u(b'{"htm":"GET"}') + "."
check("L6: alg:none proof rejected",
      rs_a.authorize(tok, none_proof, ctx())[0] is False)

print("L2 (rate limiting blunts proof floods)")
auth, _, _ = fleet()
rs = ResourceServer(auth.jwks(), auth.issuer, AUD, InMemoryAtomicStore(),
                    InMemoryAtomicStore(), auth.revocations,
                    rate_limiter=TokenBucketRateLimiter(rate_per_sec=0.0, burst=3))
tok, _, _ = auth.issue_bound_token("a", alice.jwk(AUD), AUD)
results = [rs.authorize(tok, alice.make_proof(M, URL, tok, AUD), ctx())
           for _ in range(6)]
check("L2: floods eventually rate-limited",
      any(r[2] == "rate_limited" for r in results))

print("\nALL %d CHECKS PASSED" % passed)