Skip to content

Wipe the KEX shared secret once keys are derived #1275

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ejohnstown wants to merge 1 commit into
base: master
Choose a base branch
from
Open

Wipe the KEX shared secret once keys are derived #1275

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 16 additions & 0 deletions src/internal.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3700,6 +3700,12 @@ static int GenerateKeys(WOLFSSH* ssh, byte hashId, byte doKeyPad)
}
#endif /* SHOW_SECRETS */

/* Do not keep a partial key set from a failed derivation. */
if (ret != WS_SUCCESS && cK != NULL) {
WS_FORCEZERO(cK, sizeof(Keys));
WS_FORCEZERO(sK, sizeof(Keys));
}

return ret;
}

Expand Down Expand Up @@ -8914,6 +8920,10 @@ static int DoKexDhReply(WOLFSSH* ssh, byte* buf, word32 len, word32* idx)
ret = SendNewKeys(ssh);
}

/* K is only needed to derive the keys. Wipe all of it, success or not. */
WS_FORCEZERO(ssh->k, sizeof(ssh->k));
ssh->kSz = 0;
Comment on lines +8923 to +8925

if (sigKeyBlock_ptr)
WFREE(sigKeyBlock_ptr, ssh->ctx->heap, DYNTYPE_PRIVKEY);
/* RFC 4253 11.1: WS_PUBKEY_REJECTED_E here is only the host key check,
Expand Down Expand Up @@ -18675,6 +18685,12 @@ int SendKexDhReply(WOLFSSH* ssh)
if (ret != WS_WANT_WRITE && ret != WS_SUCCESS)
PurgePacket(ssh);

/* K is only needed to derive the keys. Wipe all of it, success or not. */
if (ssh != NULL) {
WS_FORCEZERO(ssh->k, sizeof(ssh->k));
ssh->kSz = 0;
}

WLOG(WS_LOG_DEBUG, "Leaving SendKexDhReply(), ret = %d", ret);
if (sigKeyBlock_ptr) {
WS_FORCEZERO(sigKeyBlock_ptr, sizeof(struct wolfSSH_sigKeyBlockFull));
Expand Down
67 changes: 67 additions & 0 deletions tests/regress.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1500,6 +1500,17 @@ static void RunKexReplyHandshake(KexReplyHarness* harness,
result->steps = REGRESS_MAX_HANDSHAKE_STEPS;
}

/* The shared secret K does not outlive the key exchange. */
static void AssertKexSecretWiped(const WOLFSSH* ssh)
{
word32 i;

AssertIntEQ(ssh->kSz, 0);
for (i = 0; i < (word32)sizeof(ssh->k); i++) {
AssertIntEQ(ssh->k[i], 0);
}
}

static void AssertHandshakeSucceeds(const char* keyAlgo, const char* keyPath)
{
KexReplyHarness harness;
Expand All @@ -1511,6 +1522,8 @@ static void AssertHandshakeSucceeds(const char* keyAlgo, const char* keyPath)

AssertTrue(result.clientSuccess);
AssertTrue(result.serverSuccess);
AssertKexSecretWiped(harness.client);
AssertKexSecretWiped(harness.server);
AssertIntEQ(harness.mutator.mutatedPackets, 0);
AssertIntEQ(harness.client->connectState, CONNECT_SERVER_CHANNEL_REQUEST_DONE);
AssertIntEQ(harness.server->acceptState, ACCEPT_CLIENT_SESSION_ESTABLISHED);
Expand Down Expand Up @@ -1919,10 +1932,55 @@ static void AssertHandshakeRejectsCorruptedSig(const char* keyAlgo,
AssertTrue(result.clientErr != WS_WANT_READ &&
result.clientErr != WS_WANT_WRITE);
AssertIntEQ(result.clientErr, expectedErr);
/* K was agreed before the verify failed. */
AssertKexSecretWiped(harness.client);

FreeKexReplyHarness(&harness);
}

/* Every key agreement, the ML-KEM hybrids included, wipes K on both sides. */
static void TestKexSecretWipedPerKex(void)
{
static const char* kexAlgos[] = {
#ifndef WOLFSSH_NO_DH_GROUP14_SHA256
"diffie-hellman-group14-sha256",
#endif
#ifndef WOLFSSH_NO_ECDH_SHA2_NISTP256
"ecdh-sha2-nistp256",
#endif
#ifndef WOLFSSH_NO_CURVE25519_SHA256
"curve25519-sha256",
#endif
#ifndef WOLFSSH_NO_NISTP256_MLKEM768_SHA256
"mlkem768nistp256-sha256",
#endif
#ifndef WOLFSSH_NO_NISTP384_MLKEM1024_SHA384
"mlkem1024nistp384-sha384",
#endif
#ifndef WOLFSSH_NO_CURVE25519_MLKEM768_SHA256
"mlkem768x25519-sha256",
#endif
NULL
Comment on lines +1960 to +1963
};
KexReplyHarness harness;
KexReplyRunResult result;
word32 i;

for (i = 0; kexAlgos[i] != NULL; i++) {
InitKexReplyHarnessKex(&harness, kexAlgos[i],
REGRESS_DEFAULT_KEY_ALGO, REGRESS_DEFAULT_KEY_PATH, 0,
REGRESS_MUTATE_SIG_NAME, NULL, 0);
RunKexReplyHandshake(&harness, &result);

AssertTrue(result.clientSuccess);
AssertTrue(result.serverSuccess);
AssertKexSecretWiped(harness.client);
AssertKexSecretWiped(harness.server);

FreeKexReplyHarness(&harness);
}
}

#ifndef WOLFSSH_NO_RSA_SHA2_256
static void TestKexDhReplyRejectsRsaSha2_256CorruptSig(void)
{
Expand Down Expand Up @@ -15674,6 +15732,7 @@ static void TestGenerateKeysSplit(void)
word32 payloadSz;
word32 idx;
byte zeros[AES_256_KEY_SIZE];
Keys zeroKeys;

WMEMSET(zeros, 0, sizeof(zeros));

Expand Down Expand Up @@ -15741,6 +15800,13 @@ static void TestGenerateKeysSplit(void)
AssertTrue(WMEMCMP(ssh->handshake->peerKeys.encKey,
ssh->handshake->keys.encKey, AES_128_KEY_SIZE) != 0);

/* A failed derivation leaves no key material behind. */
AssertTrue(wolfSSH_TestGenerateKeys(ssh, WC_HASH_TYPE_NONE) != WS_SUCCESS);
WMEMSET(&zeroKeys, 0, sizeof(zeroKeys));
AssertTrue(WMEMCMP(&ssh->handshake->keys, &zeroKeys, sizeof(Keys)) == 0);
AssertTrue(WMEMCMP(&ssh->handshake->peerKeys, &zeroKeys,
sizeof(Keys)) == 0);

wolfSSH_free(ssh);

#ifndef WOLFSSH_NO_AES_GCM
Expand Down Expand Up @@ -17406,6 +17472,7 @@ int main(int argc, char** argv)
TestKexDhReplyRejectsEd25519CorruptSig();
#endif
TestKexDhReplyRejectsSigNameOverrun();
TestKexSecretWipedPerKex();
#ifdef REGRESS_TRUNC_KEX_ALGO
TestKexDhReplyTruncatedFSendsDisconnect();
TestKexDhInitTruncatedESendsDisconnect();
Expand Down
Loading