diff --git a/defs/.gitignore b/defs/.gitignore
index e42d9910a..a6c57f5fb 100644
--- a/defs/.gitignore
+++ b/defs/.gitignore
@@ -1 +1 @@
-coins.json
+*.json
diff --git a/defs/coins/combine.py b/defs/coins/combine.py
index 0d0b79dcb..cdd08b775 100755
--- a/defs/coins/combine.py
+++ b/defs/coins/combine.py
@@ -3,6 +3,8 @@
 import json
 import glob
 import re
+from hashlib import sha256
+import ed25519
 
 
 def check_type(val, types, nullable=False, empty=False, regex=None, choice=None):
@@ -78,18 +80,36 @@ def validate_coin(coin):
         assert not bc.endswith('/')
 
 
+def serialize(coin):
+    # TODO: replace with protobuf serialization
+    return json.dumps(coin).encode()
+
+
+def sign(data):
+    h = sha256(data).digest()
+    sign_key = ed25519.SigningKey(b'A' * 32)
+    return sign_key.sign(h)
+
+
 def process_json(fn):
     print(fn, end=' ... ')
     j = json.load(open(fn))
     validate_coin(j)
+    ser = serialize(j)
+    sig = sign(ser)
+    definition = (sig + ser).hex()
     print('OK')
-    return j
+    return j, definition
 
 
 coins = {}
+defs = {}
 for fn in glob.glob('*.json'):
-    c = process_json(fn)
+    c, d = process_json(fn)
     n = c['coin_name']
     coins[n] = c
+    defs[n] = d
+
 
 json.dump(coins, open('../coins.json', 'w'), indent=4, sort_keys=True)
+json.dump(defs, open('../coindefs.json', 'w'), indent=4, sort_keys=True)
diff --git a/defs/coins/schema.proto b/defs/coins/schema.proto
index 88d13f9b8..912e45f8e 100644
--- a/defs/coins/schema.proto
+++ b/defs/coins/schema.proto
@@ -22,8 +22,8 @@ message CoinDef {
 	optional uint32 fork_id = 20;
 	optional bool force_bip143 = 21;
 	optional uint64 dust_limit = 22;
-	optional uint32 blocktime_seconds = 23;
-	optional string address_prefix = 24;
-	optional uint32 min_address_length = 25;
-	optional uint32 max_address_length = 26;
+	optional string address_prefix = 23;
+	optional uint32 min_address_length = 24;
+	optional uint32 max_address_length = 25;
+	optional bytes icon = 26;
 }