From d76a15ec896dddb021ef8aeb9f77bba34dadd27b Mon Sep 17 00:00:00 2001
From: Daniel Larimer <dan@bitshares.org>
Date: Thu, 23 Jul 2015 18:45:35 -0400
Subject: [PATCH] adding child key derivation for ecc keys

---
 include/fc/crypto/elliptic.hpp |  4 ++++
 src/crypto/elliptic_common.cpp | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/fc/crypto/elliptic.hpp b/include/fc/crypto/elliptic.hpp
index 31e50a0..b05dc58 100644
--- a/include/fc/crypto/elliptic.hpp
+++ b/include/fc/crypto/elliptic.hpp
@@ -46,6 +46,8 @@ namespace fc {
            public_key( const public_key_point_data& v );
            public_key( const compact_signature& c, const fc::sha256& digest, bool check_canonical = true );
 
+           public_key child( const fc::sha256& offset )const;
+
            bool valid()const;
            /** Computes new pubkey = generator * offset + old pubkey ?! */
 //           public_key mult( const fc::sha256& offset )const;
@@ -96,6 +98,8 @@ namespace fc {
            static private_key generate();
            static private_key regenerate( const fc::sha256& secret );
 
+           private_key child( const fc::sha256& offset )const;
+
            /**
             *  This method of generation enables creating a new private key in a deterministic manner relative to
             *  an initial seed.   A public_key created from the seed can be multiplied by the offset to calculate
diff --git a/src/crypto/elliptic_common.cpp b/src/crypto/elliptic_common.cpp
index 741682e..a66c26b 100644
--- a/src/crypto/elliptic_common.cpp
+++ b/src/crypto/elliptic_common.cpp
@@ -1,5 +1,6 @@
 #include <fc/crypto/base58.hpp>
 #include <fc/crypto/elliptic.hpp>
+#include <fc/io/raw.hpp>
 
 /* stuff common to all ecc implementations */
 
@@ -9,6 +10,23 @@ namespace fc { namespace ecc {
         return public_key(data);
     }
 
+    public_key public_key::child( const fc::sha256& offset )const
+    {
+       fc::sha256::encoder enc;
+       fc::raw::pack( enc, *this );
+       fc::raw::pack( enc, offset );
+
+       return add( enc.result() );
+    }
+
+    private_key private_key::child( const fc::sha256& offset )const
+    {
+       fc::sha256::encoder enc;
+       fc::raw::pack( enc, get_public_key() );
+       fc::raw::pack( enc, offset );
+       return generate_from_seed( get_secret(), enc.result() );
+    }
+
     std::string public_key::to_base58( const public_key_data &key )
     {
       uint32_t check = (uint32_t)sha256::hash(key.data, sizeof(key))._hash[0];