From df51dbe17f6c31eecef309cd7ccaa39bf9808b11 Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Mon, 18 Feb 2019 16:41:55 +0000
Subject: [PATCH] Add fields for PSA-based ECDHE to handshake structure

This is the first in a series of commits adding client-side
support for PSA-based ECDHE.

Previously, the state of an ECDHE key agreement was maintained
in the field mbedtls_ssl_handshake_params::ecdh_ctx, of type
::mbedtls_ecdh_context and manipulated through the ECDH API.

The ECDH API will be superseeded by the PSA Crypto API for key
agreement, which needs the following data:
(a) A raw buffer holding the public part of the key agreement
    received from our peer.
(b) A key slot holding the private part of the key agreement.
(c) The algorithm to use.
The commit adds fields to ::mbedtls_ssl_handshake_params
representing these three inputs to PSA-based key agreement.

Specifically, it adds a field for the key slot holding the
ECDH private key, a field for the EC curve identifier, and
a buffer holding the peer's public key.

Note: Storing the peer's public key buffer is slightly
inefficient, as one could perform the ECDH computation
as soon as the peer sends its public key, either working
with in-place or using a stack-buffer to reformat the
public key before passing it to PSA. This optimization
is left for a later commit.
---
 include/mbedtls/psa_util.h     |  2 ++
 include/mbedtls/ssl_internal.h | 15 ++++++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/mbedtls/psa_util.h b/include/mbedtls/psa_util.h
index dca4fa4f5..a678a777a 100644
--- a/include/mbedtls/psa_util.h
+++ b/include/mbedtls/psa_util.h
@@ -235,6 +235,8 @@ static inline int mbedtls_psa_get_ecc_oid_from_id(
      return( -1 );
 }
 
+#define MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH 256
+
 static inline psa_ecc_curve_t mbedtls_psa_translate_ecc_group( mbedtls_ecp_group_id grpid )
 {
     switch( grpid )
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 3159cd32b..be7f41b1d 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -57,6 +57,11 @@
 #include "ecjpake.h"
 #endif
 
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "psa/crypto.h"
+#include "psa_util.h"
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
 #if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
     !defined(inline) && !defined(__cplusplus)
 #define inline __inline
@@ -280,7 +285,15 @@ struct mbedtls_ssl_handshake_params
 #endif
 #if defined(MBEDTLS_ECDH_C)
     mbedtls_ecdh_context ecdh_ctx;              /*!<  ECDH key exchange       */
-#endif
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_ecc_curve_t ecdh_psa_curve;
+    psa_key_handle_t ecdh_psa_privkey;
+    unsigned char ecdh_psa_peerkey[MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH];
+    size_t ecdh_psa_peerkey_len;
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+#endif /* MBEDTLS_ECDH_C */
+
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
     mbedtls_ecjpake_context ecjpake_ctx;        /*!< EC J-PAKE key exchange */
 #if defined(MBEDTLS_SSL_CLI_C)