Allow maximum label length in Hkdf-Expand-Label
Previously, the length of the label was limited to the maximal length
that would be used in the TLS 1.3 key schedule. With the keying material
exporter, labels of up to 249 bytes may be used.
Signed-off-by: Max Fillinger <maximilian.fillinger@foxcrypto.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index 895176d..ff4aa0e 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -64,7 +64,7 @@
* hardcoding the writing of the high bytes.
* - (label, label_len): label + label length, without "tls13 " prefix
* The label length MUST be less than or equal to
- * MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN
+ * MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN.
* It is the caller's responsibility to ensure this.
* All (label, label length) pairs used in TLS 1.3
* can be obtained via MBEDTLS_SSL_TLS1_3_LBL_WITH_LEN().
@@ -91,7 +91,7 @@
#define SSL_TLS1_3_KEY_SCHEDULE_MAX_HKDF_LABEL_LEN \
SSL_TLS1_3_KEY_SCHEDULE_HKDF_LABEL_LEN( \
sizeof(tls13_label_prefix) + \
- MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN, \
+ MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN, \
MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_CONTEXT_LEN)
static void ssl_tls13_hkdf_encode_label(
@@ -147,7 +147,7 @@
psa_key_derivation_operation_t operation =
PSA_KEY_DERIVATION_OPERATION_INIT;
- if (label_len > MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN) {
+ if (label_len > MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN) {
/* Should never happen since this is an internal
* function, and we know statically which labels
* are allowed. */
diff --git a/library/ssl_tls13_keys.h b/library/ssl_tls13_keys.h
index 31ffe44..14f6e48 100644
--- a/library/ssl_tls13_keys.h
+++ b/library/ssl_tls13_keys.h
@@ -60,8 +60,9 @@
mbedtls_ssl_tls13_labels.LABEL, \
MBEDTLS_SSL_TLS1_3_LBL_LEN(LABEL)
-#define MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN \
- sizeof(union mbedtls_ssl_tls13_labels_union)
+/* Maximum length of the label field in the HkdfLabel struct defined in
+ * RFC 8446, Section 7.1, excluding the "tls13 " prefix. */
+#define MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN 249
/* The maximum length of HKDF contexts used in the TLS 1.3 standard.
* Since contexts are always hashes of message transcripts, this can