[PATCH 3/4] tls: DHE_RSA key exchange implementation server side

[Andrew Zaborowski <andrew.zaborowski@intel.com>]

[-- Attachment #1: Type: text/plain, Size: 7940 bytes --]

Add the handler for the ClientKeyExchange message and a builder callback
for the ServerKeyExchange message for DHE_RSA.
---
 ell/tls-suites.c | 187 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 187 insertions(+)

diff --git a/ell/tls-suites.c b/ell/tls-suites.c
index 14ea470..b9fdc0f 100644
--- a/ell/tls-suites.c
+++ b/ell/tls-suites.c
@@ -691,6 +691,34 @@ static struct tls_key_exchange_algorithm tls_ecdhe_rsa = {
 /* Maximum FF DH prime modulus size in bytes */
 #define TLS_DHE_MAX_SIZE 1024
 
+/* RFC 3526, Section 3 */
+static const uint8_t tls_dh14_prime[] = {
+	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc9, 0x0f, 0xda, 0xa2,
+	0x21, 0x68, 0xc2, 0x34, 0xc4, 0xc6, 0x62, 0x8b, 0x80, 0xdc, 0x1c, 0xd1,
+	0x29, 0x02, 0x4e, 0x08, 0x8a, 0x67, 0xcc, 0x74, 0x02, 0x0b, 0xbe, 0xa6,
+	0x3b, 0x13, 0x9b, 0x22, 0x51, 0x4a, 0x08, 0x79, 0x8e, 0x34, 0x04, 0xdd,
+	0xef, 0x95, 0x19, 0xb3, 0xcd, 0x3a, 0x43, 0x1b, 0x30, 0x2b, 0x0a, 0x6d,
+	0xf2, 0x5f, 0x14, 0x37, 0x4f, 0xe1, 0x35, 0x6d, 0x6d, 0x51, 0xc2, 0x45,
+	0xe4, 0x85, 0xb5, 0x76, 0x62, 0x5e, 0x7e, 0xc6, 0xf4, 0x4c, 0x42, 0xe9,
+	0xa6, 0x37, 0xed, 0x6b, 0x0b, 0xff, 0x5c, 0xb6, 0xf4, 0x06, 0xb7, 0xed,
+	0xee, 0x38, 0x6b, 0xfb, 0x5a, 0x89, 0x9f, 0xa5, 0xae, 0x9f, 0x24, 0x11,
+	0x7c, 0x4b, 0x1f, 0xe6, 0x49, 0x28, 0x66, 0x51, 0xec, 0xe4, 0x5b, 0x3d,
+	0xc2, 0x00, 0x7c, 0xb8, 0xa1, 0x63, 0xbf, 0x05, 0x98, 0xda, 0x48, 0x36,
+	0x1c, 0x55, 0xd3, 0x9a, 0x69, 0x16, 0x3f, 0xa8, 0xfd, 0x24, 0xcf, 0x5f,
+	0x83, 0x65, 0x5d, 0x23, 0xdc, 0xa3, 0xad, 0x96, 0x1c, 0x62, 0xf3, 0x56,
+	0x20, 0x85, 0x52, 0xbb, 0x9e, 0xd5, 0x29, 0x07, 0x70, 0x96, 0x96, 0x6d,
+	0x67, 0x0c, 0x35, 0x4e, 0x4a, 0xbc, 0x98, 0x04, 0xf1, 0x74, 0x6c, 0x08,
+	0xca, 0x18, 0x21, 0x7c, 0x32, 0x90, 0x5e, 0x46, 0x2e, 0x36, 0xce, 0x3b,
+	0xe3, 0x9e, 0x77, 0x2c, 0x18, 0x0e, 0x86, 0x03, 0x9b, 0x27, 0x83, 0xa2,
+	0xec, 0x07, 0xa2, 0x8f, 0xb5, 0xc5, 0x5d, 0xf0, 0x6f, 0x4c, 0x52, 0xc9,
+	0xde, 0x2b, 0xcb, 0xf6, 0x95, 0x58, 0x17, 0x18, 0x39, 0x95, 0x49, 0x7c,
+	0xea, 0x95, 0x6a, 0xe5, 0x15, 0xd2, 0x26, 0x18, 0x98, 0xfa, 0x05, 0x10,
+	0x15, 0x72, 0x8e, 0x5a, 0x8a, 0xac, 0xaa, 0x68, 0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+};
+
+static const unsigned int tls_dh14_generator = 2;
+
 struct tls_dhe_params {
 	size_t prime_len;
 	struct l_key *prime;
@@ -758,6 +786,100 @@ static bool tls_get_server_dh_params_hash(struct l_tls *tls, uint8_t tls_id,
 	return true;
 }
 
+static bool tls_send_dhe_server_key_xchg(struct l_tls *tls)
+{
+	uint8_t buf[1024 + TLS_DHE_MAX_SIZE * 3];
+	uint8_t *ptr = buf + TLS_HANDSHAKE_HEADER_SIZE;
+	struct tls_dhe_params *params;
+	const uint8_t *prime_buf;
+	uint8_t generator_buf = tls_dh14_generator;
+	uint8_t public_buf[TLS_DHE_MAX_SIZE];
+	size_t public_len;
+	unsigned int zeros = 0;
+	ssize_t sign_len;
+
+	params = l_new(struct tls_dhe_params, 1);
+
+	/*
+	 * For now hardcode the Oakley Group 14 parameters like some other
+	 * TLS implementations do without RFC 7919, which is actually a
+	 * downside because the more common the group parameters are the
+	 * less secure they are assumed to be, but also is a test that the
+	 * group is sufficiently good.
+	 *
+	 * Eventually we should make this configurable so that a unique
+	 * likely-prime number generated by either 'openssl dhparam' or
+	 * 'ssh-keygen -G' can be set, or parse /etc/ssh/moduli to select
+	 * a random pre-generated FFDH group each time.
+	 */
+	prime_buf = tls_dh14_prime;
+	params->prime_len = sizeof(tls_dh14_prime);
+
+	params->prime = l_key_new(L_KEY_RAW, prime_buf, params->prime_len);
+	params->generator = l_key_new(L_KEY_RAW, &generator_buf, 1);
+
+	if (!params->prime || !params->generator) {
+		TLS_DISCONNECT(TLS_ALERT_INTERNAL_ERROR, 0, "l_key_new failed");
+		goto free_params;
+	}
+
+	params->private = l_key_generate_dh_private(prime_buf, params->prime_len);
+	if (!params->private) {
+		TLS_DISCONNECT(TLS_ALERT_INTERNAL_ERROR, 0,
+				"l_key_generate_dh_private failed");
+		goto free_params;
+	}
+
+	public_len = params->prime_len;
+
+	if (!l_key_compute_dh_public(params->generator, params->private,
+					params->prime, public_buf,
+					&public_len)) {
+		TLS_DISCONNECT(TLS_ALERT_INTERNAL_ERROR, 0,
+				"l_key_compute_dh_public failed");
+		goto free_params;
+	}
+
+	while (zeros < public_len && public_buf[zeros] == 0x00)
+		zeros++;
+
+	params->server_dh_params_buf = ptr;
+
+	/* RFC 5246, Section 7.4.3 */
+
+	l_put_be16(params->prime_len, ptr);
+	memcpy(ptr + 2, prime_buf, params->prime_len);
+	ptr += 2 + params->prime_len;
+
+	l_put_be16(1, ptr);
+	memcpy(ptr + 2, &generator_buf, 1);
+	ptr += 2 + 1;
+
+	l_put_be16(public_len - zeros, ptr);
+	memcpy(ptr + 2, public_buf + zeros, public_len - zeros);
+	ptr += 2 + public_len - zeros;
+
+	params->server_dh_params_len = ptr - params->server_dh_params_buf;
+	tls->pending.key_xchg_params = params;
+
+	sign_len = tls->pending.cipher_suite->key_xchg->sign(tls, ptr,
+					buf + sizeof(buf) - ptr,
+					tls_get_server_dh_params_hash);
+	if (sign_len < 0)
+		return false;
+
+	ptr += sign_len;
+	tls_tx_handshake(tls, TLS_SERVER_KEY_EXCHANGE, buf, ptr - buf);
+	return true;
+
+free_params:
+	l_key_free(params->prime);
+	l_key_free(params->generator);
+	l_key_free(params->private);
+	l_free(params);
+	return false;
+}
+
 static void tls_handle_dhe_server_key_xchg(struct l_tls *tls,
 						const uint8_t *buf, size_t len)
 {
@@ -937,13 +1059,78 @@ static bool tls_send_dhe_client_key_xchg(struct l_tls *tls)
 	return true;
 }
 
+static void tls_handle_dhe_client_key_xchg(struct l_tls *tls,
+						const uint8_t *buf, size_t len)
+{
+	struct tls_dhe_params *params = tls->pending.key_xchg_params;
+	uint8_t pre_master_secret[params->prime_len];
+	size_t pre_master_secret_len;
+	size_t public_len;
+	unsigned int zeros = 0;
+
+	if (len < 2)
+		goto decode_error;
+
+	public_len = l_get_be16(buf);
+	buf += 2;
+	len -= 2;
+
+	if (public_len != len)
+		goto decode_error;
+
+	/*
+	 * RFC 7919 Section 4:
+	 * "the server MUST verify that 1 < dh_Yc < dh_p - 1.  If dh_Yc is
+	 * out of range, the server MUST terminate the connection with
+	 * a fatal handshake_failure(40) alert."
+	 */
+	if (!l_key_validate_dh_payload(buf, public_len,
+					tls_dh14_prime, params->prime_len)) {
+		TLS_DISCONNECT(TLS_ALERT_HANDSHAKE_FAIL, 0,
+				"Client DH public value invalid");
+		return;
+	}
+
+	params->public = l_key_new(L_KEY_RAW, buf, public_len);
+	if (!params->prime) {
+		TLS_DISCONNECT(TLS_ALERT_INTERNAL_ERROR, 0, "l_key_new failed");
+		return;
+	}
+
+	pre_master_secret_len = params->prime_len;
+
+	if (!l_key_compute_dh_secret(params->public, params->private,
+					params->prime, pre_master_secret,
+					&pre_master_secret_len)) {
+		TLS_DISCONNECT(TLS_ALERT_INTERNAL_ERROR, 0,
+				"Generating DH shared-secret failed");
+		return;
+	}
+
+	while (zeros < pre_master_secret_len &&
+			pre_master_secret[zeros] == 0x00)
+		zeros++;
+
+	tls_free_dhe_params(tls);
+	tls_generate_master_secret(tls, pre_master_secret + zeros,
+					pre_master_secret_len - zeros);
+	memset(pre_master_secret, 0, pre_master_secret_len);
+	return;
+
+decode_error:
+	TLS_DISCONNECT(TLS_ALERT_DECODE_ERROR, 0,
+			"ClientKeyExchange decode error");
+}
+
 static struct tls_key_exchange_algorithm tls_dhe_rsa = {
 	.id = 1, /* RSA_sign */
 	.certificate_check = true,
 	.need_ecc = true,
 	.validate_cert_key_type = tls_rsa_validate_cert_key,
+	.send_server_key_exchange = tls_send_dhe_server_key_xchg,
 	.handle_server_key_exchange = tls_handle_dhe_server_key_xchg,
 	.send_client_key_exchange = tls_send_dhe_client_key_xchg,
+	.handle_client_key_exchange = tls_handle_dhe_client_key_xchg,
 	.free_params = tls_free_dhe_params,
 	.sign = tls_rsa_sign,
 	.verify = tls_rsa_verify,
-- 
2.19.1