From 00d613728fdddf4f28e3c50cb2f70bfbba65e298 Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Sat, 8 Aug 2015 19:52:05 +0200
Subject: completing TALER_MINT_refresh_melt implementation

---
 src/util/crypto.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

(limited to 'src/util/crypto.c')

diff --git a/src/util/crypto.c b/src/util/crypto.c
index b803b960a..edc300878 100644
--- a/src/util/crypto.c
+++ b/src/util/crypto.c
@@ -162,6 +162,34 @@ TALER_transfer_decrypt (const struct TALER_EncryptedLinkSecretP *secret_enc,
 }
 
 
+/**
+ * Given the coin and the transfer private keys, compute the
+ * transfer secret.  (Technically, we only need one of the two
+ * private keys, but the caller currently trivially only has
+ * the two private keys, so we derive one of the public keys
+ * internally to this function.)
+ *
+ * @param coin_priv coin key
+ * @param trans_priv transfer private key
+ * @param[out] computed transfer secret
+ */
+void
+TALER_link_derive_transfer_secret (const struct TALER_CoinSpendPrivateKeyP *coin_priv,
+                                   const struct TALER_TransferPrivateKeyP *trans_priv,
+                                   struct TALER_TransferSecretP *ts)
+{
+  struct TALER_CoinSpendPublicKeyP coin_pub;
+
+  GNUNET_CRYPTO_eddsa_key_get_public (&coin_priv->eddsa_priv,
+                                      &coin_pub.eddsa_pub);
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_CRYPTO_ecdh_eddsa (&trans_priv->ecdhe_priv,
+                                           &coin_pub.eddsa_pub,
+                                           &ts->key));
+
+}
+
+
 /**
  * Use the @a trans_sec (from ECDHE) to encrypt the @a secret
  * to obtain the @a secret_enc.
-- 
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