Try to prevent some misuse of RSA functions
fixes #331
diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index e5e78fb..458bb51 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -321,7 +321,7 @@
/**
* \brief Make signature, including padding if relevant.
*
- * \param ctx PK context to use
+ * \param ctx PK context to use - must hold a private key
* \param md_alg Hash algorithm used (see notes)
* \param hash Hash of the message to sign
* \param hash_len Hash length or 0 (see notes)
@@ -350,7 +350,7 @@
/**
* \brief Decrypt message (including padding if relevant).
*
- * \param ctx PK context to use
+ * \param ctx PK context to use - must hold a private key
* \param input Input to decrypt
* \param ilen Input size
* \param output Decrypted output