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fix(a7-auth): address SCRAM auth review findings A-G

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- tests: pass CREDENTIAL_KEY_LEN to unhex for the 32-byte KAT proof/sig
  (sizeof(expect) is 348, over-reading the 65-byte hex literal under ASan)
- credentials: close the username-enumeration oracle with a store-wide
  dummy_key and a deterministic per-username dummy salt; make the store's
  iteration count uniform (reject intra-file and layered disagreements) and
  answer a miss with the store-wide count; run the constant-time key compare
  even when found=false and fold the decision with bitwise AND
- credentials_compute_keys: enforce [CREDENTIAL_MIN_ITERS, CREDENTIAL_MAX_ITERS]
- tests: recompute the whole KAT independently at CREDENTIAL_DEFAULT_ITERS
  (600000) and pin the golden store line; add non-uniform-store rejection,
  bound and deterministic-dummy-salt assertions
- server: send exactly one generic STATUS_AUTH_FAILED on every failure path
  (including credentials_get_verifier failure); route all handshake exits
  through one burn path
- credentials/server: burn the base64 decoders' scratch on error, the
  hash_store_line base64/line buffers on failure, and all handshake key/proof
  material
- fuzz: guard the auth-offset scan against size_t underflow and use a found flag
- docs: drop stale digest wording, use CREDENTIAL_MIN_ITERS as the --iterations
  bound, document 0600 output for --hash-credentials (plus a stderr warning on
  a group/other-accessible stdout file), and describe the deterministic dummy
  salt in the no-oracle claims
This commit is contained in:
TapTap
2026-09-12 17:56:52 +02:00
parent 8c94ec9886
commit eaf67f6257
10 changed files with 302 additions and 112 deletions
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tests/test_credentials.c
+101 -13
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@@ -11,17 +11,21 @@
#include <unistd.h>
/* Known-answer vector, independently recomputed with Python
* (hashlib.pbkdf2_hmac / hmac / hashlib.sha256). */
* (hashlib.pbkdf2_hmac / hmac / hashlib.sha256) at the default work factor. */
#define KAT_PASSWORD "alice-s3cret"
#define KAT_USER "alice"
#define KAT_ITERS 4096u
#define KAT_CLIENT_KEY "80f0e0af43e34e8aeec1738609c5d1eac8646601b4f244cef5a04a9f13563cf8"
#define KAT_STORED_KEY "5b3b489437085a11fe594ab99154da4cb4ebab4ae8c2edf51fbaa9277e9f9099"
#define KAT_SERVER_KEY "38f668736210bd4dbcb5193b9a514c5b1047174eff5f5a80ee4c2b1e8b2c76a1"
#define KAT_CLIENT_PROOF "c9b0d397b853176b842a751b9af327270ae0c5e286cb77d16e59fa42245270f6"
#define KAT_SERVER_SIG "93c0d94b9ee29798ffd42734a9becb2168bad1f69e492d2ccb042a43db13bffc"
#define KAT_ITERS CREDENTIAL_DEFAULT_ITERS
#define KAT_CLIENT_KEY "845891d65ab3c9807f7ae5c123ab70714cc8b56173fccfce6a758993e858e17c"
#define KAT_STORED_KEY "d192f6da1c54bf73768f0a7c713995212d303c46f809de1b2e407fb3ad1c206b"
#define KAT_SERVER_KEY "508ad587574f59700c2d0bbec8417d6fe94bf8e39669adbabe7cbbd8700f86ce"
#define KAT_CLIENT_PROOF "e0cb4b894a7438d75cbb3066aa135d10200b76eea78137c5c04059895eed9242"
#define KAT_SERVER_SIG "f564e00fa6368e78d35b7116c7624d6cb047a950d87e3799e4e6e8c8954b618a"
#define KAT_SALT_B64 "AAECAwQFBgcICQoLDA0ODw=="
#define KAT_NAME_PREFIX "$fastsync$1$pbkdf2-sha256$"
/* The exact store line for the KAT user/password at the KAT salt/count. */
#define KAT_STORE_LINE \
"alice:$fastsync$1$pbkdf2-sha256$600000$AAECAwQFBgcICQoLDA0ODw==$" \
"0ZL22hxUv3N2jwp8cTmVIS0wPEb4Cd4bLkB/s60cIGs=$UIrVh1dPWXAMLQu+yEF9b+lL+OOWaa26vny72HAPhs4="
static int g_file_counter = 0;
@@ -133,6 +137,10 @@ static void test_credentials_compute_keys_kat() {
unhex(KAT_SERVER_KEY, expect, sizeof(expect));
EXPECT_TRUE(memcmp(server_key, expect, sizeof(expect)) == 0);
EXPECT_FALSE(credentials_compute_keys(KAT_PASSWORD, salt, 0, client_key, stored_key, server_key));
EXPECT_FALSE(credentials_compute_keys(KAT_PASSWORD, salt, CREDENTIAL_MIN_ITERS - 1, client_key,
stored_key, server_key));
EXPECT_FALSE(credentials_compute_keys(KAT_PASSWORD, salt, CREDENTIAL_MAX_ITERS + 1, client_key,
stored_key, server_key));
EXPECT_FALSE(credentials_compute_keys(NULL, salt, KAT_ITERS, client_key, stored_key, server_key));
}
@@ -166,9 +174,9 @@ static void test_credentials_auth_message_and_proof_kat() {
uint8_t server_sig[CREDENTIAL_KEY_LEN];
EXPECT_TRUE(credentials_client_proof(client_key, stored_key, server_key, auth_msg, msg_len, proof,
server_sig));
unhex(KAT_CLIENT_PROOF, expect, sizeof(expect));
unhex(KAT_CLIENT_PROOF, expect, CREDENTIAL_KEY_LEN);
EXPECT_TRUE(memcmp(proof, expect, CREDENTIAL_KEY_LEN) == 0);
unhex(KAT_SERVER_SIG, expect, sizeof(expect));
unhex(KAT_SERVER_SIG, expect, CREDENTIAL_KEY_LEN);
EXPECT_TRUE(memcmp(server_sig, expect, CREDENTIAL_KEY_LEN) == 0);
}
@@ -274,6 +282,35 @@ static void test_credentials_hash_store_line_roundtrip() {
free(path);
}
/* The golden store line (KAT user/password/salt/count) parses back to exactly
* the KAT verifier keys, pinning the on-disk encoding independently. */
static void test_credentials_store_line_golden() {
char* path = make_tmp_file(KAT_STORE_LINE "\n");
EXPECT_NOT_NULL(path);
char err[512];
CredentialStore* store = credentials_load(path, NULL, err, sizeof(err));
EXPECT_NOT_NULL(store);
EXPECT_TRUE(credentials_store_has(store, "alice"));
CredentialVerifier v;
const char* module_users[] = {"alice"};
EXPECT_TRUE(credentials_get_verifier(store, "alice", module_users, 1, &v));
EXPECT_TRUE(v.found);
EXPECT_EQ_INT((int)v.iters, (int)KAT_ITERS);
uint8_t expect[CREDENTIAL_KEY_LEN];
unhex(KAT_STORED_KEY, expect, CREDENTIAL_KEY_LEN);
EXPECT_TRUE(memcmp(v.stored_key, expect, CREDENTIAL_KEY_LEN) == 0);
unhex(KAT_SERVER_KEY, expect, CREDENTIAL_KEY_LEN);
EXPECT_TRUE(memcmp(v.server_key, expect, CREDENTIAL_KEY_LEN) == 0);
uint8_t salt[CREDENTIAL_SALT_LEN];
ramp(salt, sizeof(salt), 0x00);
EXPECT_TRUE(memcmp(v.salt, salt, sizeof(salt)) == 0);
credentials_free(store);
rm_temp(path);
free(path);
}
static void test_credentials_store_parse_valid() {
char line_alice[CREDENTIAL_MAX_LINE];
char line_bob[CREDENTIAL_MAX_LINE];
@@ -308,14 +345,27 @@ static void test_credentials_store_parse_valid() {
EXPECT_TRUE(credentials_get_verifier(store, "mallory", module_users, 1, &v));
EXPECT_TRUE(memcmp(v.stored_key, zero, CREDENTIAL_KEY_LEN) == 0);
EXPECT_TRUE(memcmp(v.server_key, zero, CREDENTIAL_KEY_LEN) == 0);
/* Miss salt is fresh random on each call. */
/* Deterministic dummy challenge: the same unknown username always yields the
* same salt and iteration count, while different usernames differ, so probing
* the store twice cannot reveal membership. */
uint8_t salt_a[CREDENTIAL_SALT_LEN];
uint8_t salt_b[CREDENTIAL_SALT_LEN];
uint8_t salt_c[CREDENTIAL_SALT_LEN];
uint32_t miss_iters_a = 0;
uint32_t miss_iters_b = 0;
EXPECT_TRUE(credentials_get_verifier(store, "mallory", module_users, 1, &v));
memcpy(salt_a, v.salt, sizeof(salt_a));
miss_iters_a = v.iters;
EXPECT_TRUE(credentials_get_verifier(store, "mallory", module_users, 1, &v));
memcpy(salt_b, v.salt, sizeof(salt_b));
EXPECT_TRUE(memcmp(salt_a, salt_b, sizeof(salt_a)) != 0);
miss_iters_b = v.iters;
EXPECT_TRUE(memcmp(salt_a, salt_b, sizeof(salt_a)) == 0);
EXPECT_EQ_INT((int)miss_iters_a, (int)miss_iters_b);
/* A miss is answered with the store-wide uniform iteration count. */
EXPECT_EQ_INT((int)miss_iters_a, (int)CREDENTIAL_MIN_ITERS);
EXPECT_TRUE(credentials_get_verifier(store, "trudy", module_users, 1, &v));
memcpy(salt_c, v.salt, sizeof(salt_c));
EXPECT_TRUE(memcmp(salt_a, salt_c, sizeof(salt_a)) != 0);
credentials_free(store);
rm_temp(path);
@@ -357,8 +407,8 @@ static void test_credentials_store_parse_rejects_malformed() {
short_key,
empty_field,
"ali "
"ce:$fastsync$1$pbkdf2-sha256$600000$AAECAwQFBgcICQoLDA0ODw==$WztIlDcIWhH+"
"WUq5kVTaTLTrq0rowu31H7qpJ36fkJk=$OPZoc2IQvU28tRk7mlFMWxBHF07/X1qA7kwrHossdqE=\n",
"ce:$fastsync$1$pbkdf2-sha256$600000$AAECAwQFBgcICQoLDA0ODw==$0ZL22hxUv3N2jwp8"
"cTmVIS0wPEb4Cd4bLkB/s60cIGs=$UIrVh1dPWXAMLQu+yEF9b+lL+OOWaa26vny72HAPhs4=\n",
};
for (size_t i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
char* path = make_tmp_file(cases[i]);
@@ -401,6 +451,25 @@ static void test_credentials_store_duplicate_rejected() {
free(path);
}
/* A store must be uniform in its iteration count so a miss can be challenged
* with the store-wide count without leaking membership. */
static void test_credentials_store_rejects_nonuniform_iters() {
char line_a[CREDENTIAL_MAX_LINE];
char line_b[CREDENTIAL_MAX_LINE];
EXPECT_TRUE(make_store_line("alice", KAT_PASSWORD, CREDENTIAL_MIN_ITERS, line_a, sizeof(line_a)));
EXPECT_TRUE(
make_store_line("bob", "bob-s3cret", CREDENTIAL_MIN_ITERS * 2, line_b, sizeof(line_b)));
char contents[2 * CREDENTIAL_MAX_LINE + 8];
snprintf(contents, sizeof(contents), "%s\n%s\n", line_a, line_b);
char* path = make_tmp_file(contents);
EXPECT_NOT_NULL(path);
char err[512];
EXPECT_NULL(credentials_load(path, NULL, err, sizeof(err)));
EXPECT_TRUE(strstr(err, "uniform") != NULL);
rm_temp(path);
free(path);
}
static void test_credentials_store_parse_missing_file() {
char err[512];
const CredentialStore* store =
@@ -414,6 +483,11 @@ static void test_credentials_store_empty_and_null() {
CredentialStore* store = credentials_load(NULL, NULL, err, sizeof(err));
EXPECT_NOT_NULL(store);
EXPECT_EQ_INT(credentials_store_size(store), 0);
/* An empty store answers a miss with the default work factor. */
CredentialVerifier v;
EXPECT_TRUE(credentials_get_verifier(store, "nobody", NULL, 0, &v));
EXPECT_FALSE(v.found);
EXPECT_EQ_INT((int)v.iters, (int)CREDENTIAL_DEFAULT_ITERS);
credentials_free(store);
char* path = make_tmp_file("# nothing here\n; nor here\n");
@@ -449,19 +523,24 @@ static void test_credentials_early_input_merge() {
char alice_file[CREDENTIAL_MAX_LINE + 2];
char bob_file[CREDENTIAL_MAX_LINE + 2];
char alice_other[CREDENTIAL_MAX_LINE];
char bob_other_iters[CREDENTIAL_MAX_LINE];
snprintf(alice_file, sizeof(alice_file), "%s\n", alice);
snprintf(bob_file, sizeof(bob_file), "%s\n", bob);
EXPECT_TRUE(make_store_line("alice", "different-s3cret", CREDENTIAL_MIN_ITERS, alice_other,
sizeof(alice_other)));
EXPECT_TRUE(make_store_line("carol", "carol-s3cret", CREDENTIAL_MIN_ITERS * 2, bob_other_iters,
sizeof(bob_other_iters)));
char* pw = make_tmp_file(alice_file);
char* early = make_tmp_file(bob_file);
char* early_same = make_tmp_file(alice_file); /* byte-identical verifier dedupes */
char* early_diff = make_tmp_file(alice_other);
char* early_iters = make_tmp_file(bob_other_iters);
EXPECT_NOT_NULL(pw);
EXPECT_NOT_NULL(early);
EXPECT_NOT_NULL(early_same);
EXPECT_NOT_NULL(early_diff);
EXPECT_NOT_NULL(early_iters);
char err[512];
/* A second file adds a new user. */
@@ -483,14 +562,21 @@ static void test_credentials_early_input_merge() {
EXPECT_NULL(store);
EXPECT_TRUE(err[0] != '\0');
/* A layered store must stay uniform in its iteration count. */
store = credentials_load(pw, early_iters, err, sizeof(err));
EXPECT_NULL(store);
EXPECT_TRUE(strstr(err, "uniform") != NULL);
rm_temp(pw);
rm_temp(early);
rm_temp(early_same);
rm_temp(early_diff);
rm_temp(early_iters);
free(pw);
free(early);
free(early_same);
free(early_diff);
free(early_iters);
}
static void test_credentials_read_secret_file() {
@@ -677,10 +763,12 @@ void test_credentials(void) {
test_credentials_verify_response_kat();
test_credentials_username_valid();
test_credentials_hash_store_line_roundtrip();
test_credentials_store_line_golden();
test_credentials_store_parse_valid();
test_credentials_store_parse_rejects_malformed();
test_credentials_store_rejects_legacy_hex();
test_credentials_store_duplicate_rejected();
test_credentials_store_rejects_nonuniform_iters();
test_credentials_store_parse_missing_file();
test_credentials_store_empty_and_null();
test_credentials_store_overlong_line_rejected();