3 files changed, 25 insertions, 16 deletions
diff --git a/Makefile b/Makefile
index 4b1c189..9aef485 100644
--- a/Makefile
+++ b/Makefile
@@ -31,4 +31,4 @@ data: ge448_gen.o fe448.o sc448.o
 
 .PHONY: clean
 clean:
-	rm *.o *.out *.a
+	rm -rf *.o *.out *.a
diff --git a/defs.h b/defs.h
index 4222a11..4fc95eb 100644
--- a/defs.h
+++ b/defs.h
@@ -17,6 +17,8 @@ int crypto_sign_ed448_detached(unsigned char *sign, unsigned long long *smlen, c
 
 int crypto_sign_ed448_open_detached(const unsigned char *m, unsigned long long mlen, const unsigned char *sign, const unsigned char *pk);
 
+int crypto_sign_ed448_derive_pk(unsigned char *pk, const unsigned char *sk);
+
 int crypto_verify_57(const unsigned char *x, const unsigned char *y);
 
 #endif /* DEFS_H */
diff --git a/ed448.c b/ed448.c
index 087db5b..8c84fe2 100644
--- a/ed448.c
+++ b/ed448.c
@@ -14,23 +14,9 @@ int crypto_sign_ed448_keypair(
     unsigned char *sk)
 {
   int i;
-  sc448 scsk;
-  ge448 gepk;
-  unsigned char extsk[114];
-  sha3_ctx_t ctx;
 
   (void)getrandom(sk, 57, 0);
-  shake256_init(&ctx);
-  shake_update(&ctx, sk, 57);
-  shake_xof(&ctx);
-  shake_out(&ctx, extsk, 114);
-  extsk[56] = 0;
-  extsk[55] |= 0x80;
-  extsk[0] &= 0xFC;
-
-  sc448_from57bytes(&scsk, extsk);
-  ge448_scalarmult_base(&gepk, &scsk);
-  ge448_pack(pk, &gepk);
+  crypto_sign_ed448_derive_pk(pk, sk);
   for (i = 0; i < 57; i++)
     sk[57 + i] = pk[i];
   return 0;
@@ -122,3 +108,24 @@ int crypto_verify_57(const unsigned char *x, const unsigned char *y)
   }
   return (1 & ((differentbits - 1) >> 8)) - 1;
 }
+
+/* derive publick key from secret key, not copy */
+int crypto_sign_ed448_derive_pk(unsigned char *pk, const unsigned char *sk)
+{
+  ge448 gepk;
+  sc448 scsk;
+  unsigned char extsk[114];
+  sha3_ctx_t ctx;
+
+  shake256_init(&ctx);
+  shake_update(&ctx, sk, 57);
+  shake_xof(&ctx);
+  shake_out(&ctx, extsk, 114);
+  extsk[56] = 0;
+  extsk[55] |= 0x80;
+  extsk[0] &= 0xFC;
+  sc448_from57bytes(&scsk, extsk);
+  ge448_scalarmult_base(&gepk, &scsk);
+  ge448_pack(pk, &gepk);
+  return 0;
+}