tls13: add ecdh_read_public

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ecdh.c b/library/ecdh.c
index b72bd1f..b1d7c2a 100644
--- a/library/ecdh.c
+++ b/library/ecdh.c
@@ -31,6 +31,7 @@
 #include "mbedtls/ecdh.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
+#include "ssl_misc.h"
 
 #include "ecdh_misc.h"
 
@@ -690,6 +691,55 @@
     return mbedtls_mpi_write_binary( &ctx->z, buf, *olen );
 }
 
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+
+static int ecdh_read_tls13_public_internal( mbedtls_ecdh_context_mbed *ctx,
+                                            const unsigned char *buf,
+                                            size_t blen )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    const unsigned char *p = buf;
+
+    if( ( ret = mbedtls_ecp_tls13_read_point( &ctx->grp, &ctx->Qp, &p,
+                                              blen ) ) != 0 )
+        return( ret );
+
+    if( (size_t)( p - buf ) != blen )
+        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
+
+    return( 0 );
+}
+
+/*
+ * Parse and import the client's TLS 1.3 public value
+ */
+int mbedtls_ecdh_tls13_read_public( mbedtls_ecdh_context *ctx,
+                                    const unsigned char *buf, size_t blen )
+{
+    ECDH_VALIDATE_RET( ctx != NULL );
+    ECDH_VALIDATE_RET( buf != NULL );
+
+#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
+    return( ecdh_read_tls13_public_internal( ctx, buf, blen ) );
+#else
+    switch( ctx->var )
+    {
+#if defined(MBEDTLS_ECDH_VARIANT_EVEREST_ENABLED)
+        case MBEDTLS_ECDH_VARIANT_EVEREST:
+            return( mbedtls_everest_read_public( &ctx->ctx.everest_ecdh,
+                                                 buf, blen ) );
+#endif
+        case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
+            return( ecdh_read_tls13_public_internal( &ctx->ctx.mbed_ecdh,
+                                                     buf, blen ) );
+        default:
+            return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
+    }
+#endif
+}
+
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
+
 /*
  * Derive and export the shared secret
  */