Added key conversion function ref10->orlp-ed25519.

Related to issue [orlp#10](orlp#10) from the orlp/ed25519 repository.

CMakeLists.txt

@@ -43,6 +43,7 @@ set(ORLP_ED25519_SRC
         ${CMAKE_CURRENT_LIST_DIR}/src/verify.c
         ${CMAKE_CURRENT_LIST_DIR}/src/add_scalar.c
         ${CMAKE_CURRENT_LIST_DIR}/src/key_exchange.c
+        ${CMAKE_CURRENT_LIST_DIR}/src/key_convert.c
         )
 
 add_library(${PROJECT_NAME} ${ORLP_ED25519_SRC})

include/orlp-ed25519/ed25519.h

@@ -29,7 +29,7 @@ void ORLP_ED25519_DECLSPEC ed25519_sign(unsigned char *signature, const unsigned
 int ORLP_ED25519_DECLSPEC ed25519_verify(const unsigned char *signature, const unsigned char *message, size_t message_len, const unsigned char *public_key);
 void ORLP_ED25519_DECLSPEC ed25519_add_scalar(unsigned char *public_key, unsigned char *private_key, const unsigned char *scalar);
 void ORLP_ED25519_DECLSPEC ed25519_key_exchange(unsigned char *shared_secret, const unsigned char *public_key, const unsigned char *private_key);
-
+void ORLP_ED25519_DECLSPEC ed25519_key_convert_ref10_to_orlp(const unsigned char *private_key_ref10, unsigned char *private_key_orlp);
 
 #ifdef __cplusplus
 }

readme.md

@@ -116,6 +116,15 @@ shared secret. It is recommended to hash the shared secret before using it.
 `shared_secret` must be a 32 byte writable buffer where the shared secret will
 be stored.
 
+```c
+void ed25519_key_convert_ref10_to_orlp(const unsigned char *private_key_ref10, 
+                                       unsigned char *private_key_orlp);
+```
+
+Converts a private key generated in the ref10 format (e.g. via libsodium) into this library's private key format.
+`private_key_ref10` needs to be a 32B readable byte buffer containing the ref10 ed25519 private key.
+`private_key_orlp` must be a writable 64B output byte buffer into which the converted key shall be written.
+
 Example
 -------
 

src/key_convert.c

@@ -0,0 +1,9 @@
+#include "../include/orlp-ed25519/ed25519.h"
+#include "../include/orlp-ed25519/sha512.h"
+
+void ed25519_key_convert_ref10_to_orlp(const unsigned char *private_key_ref10, unsigned char *private_key_orlp) {
+  sha512(private_key_ref10, 32, private_key_orlp);
+  private_key_orlp[0] &= 248;
+  private_key_orlp[31] &= 63;
+  private_key_orlp[31] |= 64;
+}