Merge pull request #345 from h2o/kazuho/server-cipher-preference
knob to select cipher-suite based on server's preference
diff --git a/include/picotls.h b/include/picotls.h
index a3050c1..b7f13d2 100644
--- a/include/picotls.h
+++ b/include/picotls.h
@@ -736,6 +736,10 @@
*/
unsigned use_raw_public_keys : 1;
/**
+ * boolean indicating if the cipher-suite should be chosen based on server's preference
+ */
+ unsigned server_cipher_preference : 1;
+ /**
*
*/
ptls_encrypt_ticket_t *encrypt_ticket;
diff --git a/lib/picotls.c b/lib/picotls.c
index 210d530..aef5530 100644
--- a/lib/picotls.c
+++ b/lib/picotls.c
@@ -1571,24 +1571,37 @@
}
static int select_cipher(ptls_cipher_suite_t **selected, ptls_cipher_suite_t **candidates, const uint8_t *src,
- const uint8_t *const end)
+ const uint8_t *const end, int server_preference)
{
+ size_t found_index = SIZE_MAX;
int ret;
while (src != end) {
uint16_t id;
if ((ret = ptls_decode16(&id, &src, end)) != 0)
goto Exit;
- ptls_cipher_suite_t **c = candidates;
- for (; *c != NULL; ++c) {
- if ((*c)->id == id) {
- *selected = *c;
- return 0;
+ for (size_t i = 0; candidates[i] != NULL; ++i) {
+ if (candidates[i]->id == id) {
+ if (server_preference) {
+ /* preserve smallest matching index, and proceed to the next input */
+ if (i < found_index) {
+ found_index = i;
+ break;
+ }
+ } else {
+ /* return the pointer matching to the first input that can be used */
+ *selected = candidates[i];
+ goto Exit;
+ }
}
}
}
-
- ret = PTLS_ALERT_HANDSHAKE_FAILURE;
+ if (found_index != SIZE_MAX) {
+ *selected = candidates[found_index];
+ ret = 0;
+ } else {
+ ret = PTLS_ALERT_HANDSHAKE_FAILURE;
+ }
Exit:
return ret;
@@ -1731,7 +1744,7 @@
});
/* cipher-suite */
ptls_decode_open_block(src, end, 2, {
- if ((ret = select_cipher(selected_cipher, ctx->cipher_suites, src, end)) != 0)
+ if ((ret = select_cipher(selected_cipher, ctx->cipher_suites, src, end, ctx->server_cipher_preference)) != 0)
goto Exit;
src = end;
});
@@ -3816,7 +3829,7 @@
{ /* select (or check) cipher-suite, create key_schedule */
ptls_cipher_suite_t *cs;
if ((ret = select_cipher(&cs, tls->ctx->cipher_suites, ch->cipher_suites.base,
- ch->cipher_suites.base + ch->cipher_suites.len)) != 0)
+ ch->cipher_suites.base + ch->cipher_suites.len, tls->ctx->server_cipher_preference)) != 0)
goto Exit;
if (!is_second_flight) {
tls->cipher_suite = cs;
diff --git a/t/picotls.c b/t/picotls.c
index 74e24eb..5390a66 100644
--- a/t/picotls.c
+++ b/t/picotls.c
@@ -44,6 +44,37 @@
ok(ptls_server_name_is_ipaddr("2001:db8::2:1"));
}
+static void test_select_cipher(void)
+{
+#define C(x) ((x) >> 8) & 0xff, (x)&0xff
+
+ ptls_cipher_suite_t *selected,
+ *candidates[] = {&ptls_minicrypto_chacha20poly1305sha256, &ptls_minicrypto_aes128gcmsha256, NULL};
+
+ {
+ static const uint8_t input[] = {};
+ ok(select_cipher(&selected, candidates, input, input + sizeof(input), 0) == PTLS_ALERT_HANDSHAKE_FAILURE);
+ }
+
+ {
+ static const uint8_t input[] = {C(PTLS_CIPHER_SUITE_AES_128_GCM_SHA256), C(PTLS_CIPHER_SUITE_CHACHA20_POLY1305_SHA256)};
+ ok(select_cipher(&selected, candidates, input, input + sizeof(input), 0) == 0);
+ ok(selected == &ptls_minicrypto_aes128gcmsha256);
+ ok(select_cipher(&selected, candidates, input, input + sizeof(input), 1) == 0);
+ ok(selected == &ptls_minicrypto_chacha20poly1305sha256);
+ }
+
+ {
+ static const uint8_t input[] = {C(PTLS_CIPHER_SUITE_AES_256_GCM_SHA384), C(PTLS_CIPHER_SUITE_AES_128_GCM_SHA256)};
+ ok(select_cipher(&selected, candidates, input, input + sizeof(input), 0) == 0);
+ ok(selected == &ptls_minicrypto_aes128gcmsha256);
+ ok(select_cipher(&selected, candidates, input, input + sizeof(input), 1) == 0);
+ ok(selected == &ptls_minicrypto_aes128gcmsha256);
+ }
+
+#undef C
+}
+
ptls_context_t *ctx, *ctx_peer;
ptls_verify_certificate_t *verify_certificate;
struct st_ptls_ffx_test_variants_t ffx_variants[7];
@@ -1662,6 +1693,7 @@
void test_picotls(void)
{
subtest("is_ipaddr", test_is_ipaddr);
+ subtest("select_cypher", test_select_cipher);
subtest("sha256", test_sha256);
subtest("sha384", test_sha384);
subtest("hmac-sha256", test_hmac_sha256);
