From bb278f52ca2b32fd80966f4c81257c63010e8eee Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Tue, 5 Feb 2019 17:04:00 +0000
Subject: [PATCH] Add configuration option to remove peer CRT after handshake

---
 include/mbedtls/config.h | 22 ++++++++++++++++++++++
 include/mbedtls/ssl.h    |  8 ++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index e6abf24d5..091ce018f 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1354,6 +1354,28 @@
  */
 #define MBEDTLS_SSL_FALLBACK_SCSV
 
+/**
+ * \def MBEDTLS_SSL_KEEP_PEER_CERTIFICATE
+ *
+ * This option controls the presence of the API mbedtls_ssl_get_peer_cert()
+ * giving access to the peer's certificate after completion of the handshake.
+ *
+ * Unless you need mbedtls_ssl_peer_cert() in your application, it is
+ * recommended to disable this option for reduced RAM usage.
+ *
+ * \note If this option is disabled, mbedtls_ssl_get_peer_cert() is still
+ *       defined, but always returns \c NULL.
+ *
+ * \note This option has no influence on the protection against the
+ *       triple handshake attack. Even if it is disabled, Mbed TLS will
+ *       still ensure that certificates do not change during renegotiation,
+ *       for exaple by keeping a hash of the peer's certificate.
+ *
+ * Comment this macro to disable storing the peer's certificate
+ * after the handshake.
+ */
+#define MBEDTLS_SSL_KEEP_PEER_CERTIFICATE
+
 /**
  * \def MBEDTLS_SSL_HW_RECORD_ACCEL
  *
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index c4d6605b5..d736c2101 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -2982,8 +2982,12 @@ int mbedtls_ssl_get_max_out_record_payload( const mbedtls_ssl_context *ssl );
  * \param  ssl     The SSL context to use. This must be initialized and setup.
  *
  * \return         The current peer certificate, or \c NULL if
- *                 none is available. It is owned by the SSL context
- *                 and valid only until the next call to the SSL API.
+ *                 none is available, which might be because the chosen
+ *                 ciphersuite does not use peer certificates, or because
+ *                 #MBEDTLS_SSL_KEEP_PEER_CERTIFICATE has been disabled.
+ *                 If this functions does not return \c NULL, the returned
+ *                 certificate is owned by the SSL context and valid only
+ *                 until the next call to the SSL API.
  *
  * \note           For one-time inspection of the peer's certificate during
  *                 the handshake, consider registering an X.509 CRT verification