Add ecdh_get_params() to import from an EC key

include/polarssl/ecdh.h

@@ -33,6 +33,15 @@
 extern "C" {
 #endif
 
+/**
+ * When importing from an EC key, select if it is our key or the peer's key
+ */
+typedef enum
+{
+    POLARSSL_ECDH_OURS,
+    POLARSSL_ECDH_THEIRS,
+} ecdh_side;
+
 /**
  * \brief           ECDH context structure
  */
@@ -134,6 +143,18 @@ int ecdh_make_params( ecdh_context *ctx, size_t *olen,
 int ecdh_read_params( ecdh_context *ctx,
                       const unsigned char **buf, const unsigned char *end );
 
+/**
+ * \brief           Setup an ECDH context from an EC key
+ *
+ * \param ctx       ECDH constext to set
+ * \param key       EC key to use
+ * \param ours      Is it our key (1) or the peer's key (0) ?
+ *
+ * \return          0 if successful, or an POLARSSL_ERR_ECP_XXX error code
+ */
+int ecdh_get_params( ecdh_context *ctx, const ecp_keypair *key,
+                     ecdh_side side );
+
 /**
  * \brief           Setup and export the client's public value
  *

library/ecdh.c

@@ -165,6 +165,32 @@ int ecdh_read_params( ecdh_context *ctx,
     return 0;
 }
 
+/*
+ * Get parameters from a keypair
+ */
+int ecdh_get_params( ecdh_context *ctx, const ecp_keypair *key,
+                     ecdh_side side )
+{
+    int ret;
+
+    if( ( ret = ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 )
+        return( ret );
+
+    /* If it's not our key, just import the public part as Qp */
+    if( side == POLARSSL_ECDH_THEIRS )
+        return( ecp_copy( &ctx->Qp, &key->Q ) );
+
+    /* Our key: import public (as Q) and private parts */
+    if( side != POLARSSL_ECDH_OURS )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    if( ( ret = ecp_copy( &ctx->Q, &key->Q ) ) != 0 ||
+        ( ret = mpi_copy( &ctx->d, &key->d ) ) != 0 )
+        return( ret );
+
+    return( 0 );
+}
+
 /*
  * Setup and export the client public value
  */