Add ecdsa_context structure
diff --git a/include/polarssl/ecdsa.h b/include/polarssl/ecdsa.h
index 2ad986d..f6b1e78 100644
--- a/include/polarssl/ecdsa.h
+++ b/include/polarssl/ecdsa.h
@@ -29,6 +29,20 @@
 
 #include "polarssl/ecp.h"
 
+/**
+ * \brief           ECDSA context structure
+ */
+typedef struct
+{
+    ecp_group grp;      /*!<  ellipitic curve used          */
+    mpi d;              /*!<  secret signature key          */
+    ecp_point Q;        /*!<  public signature key          */
+    mpi r;              /*!<  first integer from signature  */
+    mpi s;              /*!<  second integer from signature */
+    int point_format;   /*!<  format for point export       */
+}
+ecdsa_context;
+
 #ifdef __cplusplus
 extern "C" {
 #endif