diff --git a/bitforge/errors.py b/bitforge/error.py
similarity index 100%
rename from bitforge/errors.py
rename to bitforge/error.py
diff --git a/bitforge/network.py b/bitforge/network.py
index b8f230e..9820e0c 100644
--- a/bitforge/network.py
+++ b/bitforge/network.py
@@ -1,23 +1,45 @@
-from collections import namedtuple
+import collections
+
+from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.asymmetric import ec
-from errors import BitforgeError, KeyValueError, StringError
 
+from bitforge import error
+
+
+class Error(error.BitforgeError):
+    pass
+
+
+class UnknownNetwork(Error, error.KeyValueError):
+    """No network with {key} matching '{value}'"""
+
+
+class InvalidNetwork(Error, error.KeyValueError):
+    """The network {key} '{value}' is already taken"""
+
+
+class InvalidField(Error, error.StringError):
+    """The field {string} is not unique and thus, not searchable"""
+
+
+BaseNetwork = collections.namedtuple('Network', [
 
-# TODO: document these fields
-# TODO: which should be unique? It should be enforced
-BaseNetwork = namedtuple('Network', [
     # Descriptors
-    'name',
-    'aliases',
+    'name',  # Main network name
+    'aliases',  # All the network aliases
+
     # Cryptography parameters
-    'curve',
+    'curve',  # Elliptic curve used for the crypto
+    'hash_function',  # Signature hashing function
+
     # Serialization magic numbers
     'pubkeyhash',
-    'wif_prefix',
+    'wif_prefix',  # Byte prefix used to identify the network in the WIF encoding
     'scripthash',
     'hd_public_key',
     'hd_private_key',
     'magic',
+
     # Network parameters
     'port',
     'seeds',
@@ -27,79 +49,74 @@
 class Network(BaseNetwork):
     """Parameters of a Bitcoin-compatible network."""
 
-    class Error(BitforgeError):
-        pass
+    UNIQUE_FIELDS = ['name', 'wif_prefix']
 
-    class UnknownNetwork(Error, KeyValueError):
-        """No network with '{key}' matching '{value}'"""
-
-    class MultipleNetworks(Error, KeyValueError):
-        """Multiple networks with '{key}' matching '{value}'"""
-
-    class ExistingNetworkName(Error, StringError):
-        """Network name '{string}' already taken"""
-
-    _networks = {}
+    _networks = []
+    _networks_by_name = {}
 
     @classmethod
     def get(cls, name, raises=True):
         """Get a network by name or alias."""
 
-        network = cls._networks.get(name, None)
+        network = cls._networks_by_name.get(name, None)
 
         if raises and network is None:
-            raise Network.UnknownNetwork('name', name)
+            raise UnknownNetwork('name', name)
 
         return network
 
-    # TODO: discuss if this method should exist at all
     @classmethod
     def get_by_field(cls, field, value, raises=True):
         """Get a network uniquely determined by a field."""
 
-        matches = []
+        if field not in cls.UNIQUE_FIELDS:
+            if raises:
+                raise InvalidField(field)
+            return None
 
         for network in cls._networks:
-            if getattr(network, field, None) == value:
-                matches.append(network)
-
-        if raises and len(matches) == 0:
-            raise Network.UnknownNetwork(field, value)
+            if getattr(network, field) == value:
+                return network
 
-        if raises and len(matches) > 1:
-            raise Network.MultipleNetworks(field, value)
-
-        if len(matches) == 1:
-            return matches[0]
+        if raises:
+            raise UnknownNetwork(field, value)
 
     def __new__(cls, **kwargs):
         network = super(Network, cls).__new__(cls, **kwargs)
-        network._register()
+
+        # Enforce all unique fields
+        for other in cls._networks:
+            for field in cls.UNIQUE_FIELDS:
+                if getattr(other, field) == getattr(network, field):
+                    raise InvalidNetwork(field, getattr(network, field))
+
+        # Enforce uniqueness of the network aliases
+        for name in [network.name] + network.aliases:
+            if name in cls._networks_by_name:
+                raise InvalidNetwork('name', name)
+            cls._networks_by_name[name] = network
+
         return network
 
-    def _register(self):
-        """Register a network by its unique name and aliases."""
+    def __repr__(self):
+        return '<Network name: {}>'.format(self.name)
 
-        for name in [self.name] + self.aliases:
-            if name in self._networks:
-                raise Network.ExistingNetworkName(name)
-            self._networks[name] = self
+    def __str__(self):
+        return self.name
 
 
 testnet = Network(
     name = 'testnet',
     aliases = [],
-
     curve = ec.SECP256K1,
-
+    hash_function = hashes.SHA256,
     pubkeyhash = 111,
     wif_prefix = 239,
     scripthash = 196,
-    hd_public_key   = 0x043587cf,
-    hd_private_key  = 0x04358394,
-    magic      = 0x0b110907,
-
-    port  = 18333,
+    hd_public_key = 0x043587cf,
+    hd_private_key = 0x04358394,
+    magic = 0x0b110907,
+    port = 18333,
     seeds = [
         'testnet-seed.bitcoin.petertodd.org',
         'testnet-seed.bluematt.me',
@@ -112,17 +129,15 @@ def _register(self):
 default = livenet = Network(
     name = 'livenet',
     aliases = ['mainnet', 'default'],
-
     curve = ec.SECP256K1,
-
+    hash_function = hashes.SHA256,
     pubkeyhash = 0x00,
     wif_prefix = 0x80,
     scripthash = 0x05,
-    hd_public_key    =  0x0488b21e,
-    hd_private_key   = 0x0488ade4,
-    magic      = 0xf9beb4d9,
-
-    port  = 8333,
+    hd_public_key = 0x0488b21e,
+    hd_private_key = 0x0488ade4,
+    magic = 0xf9beb4d9,
+    port = 8333,
     seeds = [
         'seed.bitcoin.sipa.be',
         'dnsseed.bluematt.me',