Add RNG params to private key parsing

This is necessary for the case where the public part of an EC keypair
needs to be computed from the private part - either because it was not
included (it's an optional component) or because it was compressed (a
format we can't parse).

This changes the API of two public functions: mbedtls_pk_parse_key() and
mbedtls_pk_parse_keyfile().

Tests and programs have been adapted. Some programs use a non-secure RNG
(from the test library) just to get things to compile and run; in a
future commit this should be improved in order to demonstrate best
practice.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index 5c7b2f6..dec5111 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -667,6 +667,8 @@
  *                  The empty password is not supported.
  * \param pwdlen    Size of the password in bytes.
  *                  Ignored if \p pwd is \c NULL.
+ * \param f_rng     RNG function, must not be \c NULL. Used for blinding.
+ * \param p_rng     RNG parameter
  *
  * \note            On entry, ctx must be empty, either freshly initialised
  *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
@@ -677,8 +679,9 @@
  * \return          0 if successful, or a specific PK or PEM error code
  */
 int mbedtls_pk_parse_key( mbedtls_pk_context *ctx,
-                  const unsigned char *key, size_t keylen,
-                  const unsigned char *pwd, size_t pwdlen );
+              const unsigned char *key, size_t keylen,
+              const unsigned char *pwd, size_t pwdlen,
+              int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
 
 /** \ingroup pk_module */
 /**
@@ -718,6 +721,8 @@
  *                  Pass a null-terminated string if expecting an encrypted
  *                  key; a non-encrypted key will also be accepted.
  *                  The empty password is not supported.
+ * \param f_rng     RNG function, must not be \c NULL. Used for blinding.
+ * \param p_rng     RNG parameter
  *
  * \note            On entry, ctx must be empty, either freshly initialised
  *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
@@ -728,7 +733,8 @@
  * \return          0 if successful, or a specific PK or PEM error code
  */
 int mbedtls_pk_parse_keyfile( mbedtls_pk_context *ctx,
-                      const char *path, const char *password );
+                  const char *path, const char *password,
+                  int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
 
 /** \ingroup pk_module */
 /**