Merge remote-tracking branch 'origin/master' into update-changelog

bigchaindb/core.py

@@ -136,7 +136,6 @@ class Bigchain(object):
         response = r.table('backlog').insert(signed_transaction, durability=durability).run(self.conn)
         return response
 
-    # TODO: the same `txid` can be in two different blocks
     def get_transaction(self, txid):
         """Retrieve a transaction with `txid` from bigchain.
 
@@ -151,16 +150,77 @@ class Bigchain(object):
             If no transaction with that `txid` was found it returns `None`
         """
 
-        response = r.table('bigchain').concat_map(lambda doc: doc['block']['transactions'])\
+        validity = self.get_blocks_status_containing_tx(txid)
-            .filter(lambda transaction: transaction['id'] == txid).run(self.conn)
+
+        if validity:
+            # Disregard invalid blocks, and return if there are no valid or undecided blocks
+            validity = {_id: status for _id, status in validity.items()
+                                    if status != Bigchain.BLOCK_INVALID}
+            if not validity:
+                return None
+
+            # If the transaction is in a valid or any undecided block, return it. Does not check
+            # if transactions in undecided blocks are consistent, but selects the valid block before
+            # undecided ones
+            for _id in validity:
+                target_block_id = _id
+                if validity[_id] == Bigchain.BLOCK_VALID:
+                    break
+
+            # Query the transaction in the target block and return
+            response = r.table('bigchain').get(target_block_id).get_field('block')\
+                .get_field('transactions').filter(lambda tx: tx['id'] == txid).run(self.conn)
+
+            return response[0]
+
+        else:
+            return None
+
+    def search_block_election_on_index(self, value, index):
+        """Retrieve block election information given a secondary index and value
+
+        Args:
+            value: a value to search (e.g. transaction id string, payload hash string)
+            index (str): name of a secondary index, e.g. 'transaction_id'
+
+        Returns:
+            A list of blocks with with only election information
+        """
+        # First, get information on all blocks which contain this transaction
+        response = r.table('bigchain').get_all(value, index=index)\
+            .pluck('votes', 'id', {'block': ['voters']}).run(self.conn)
+
+        return list(response)
+
+    def get_blocks_status_containing_tx(self, txid):
+        """Retrieve block ids and statuses related to a transaction
+
+        Transactions may occur in multiple blocks, but no more than one valid block.
+
+        Args:
+            txid (str): transaction id of the transaction to query
+
+        Returns:
+            A dict of blocks containing the transaction,
+            e.g. {block_id_1: 'valid', block_id_2: 'invalid' ...}, or None
+        """
+
+        # First, get information on all blocks which contain this transaction
+        blocks = self.search_block_election_on_index(txid, 'transaction_id')
+
+        if blocks:
+            # Determine the election status of each block
+            validity = {block['id']: self.block_election_status(block) for block in blocks}
+
+            # If there are multiple valid blocks with this transaction, something has gone wrong
+            if list(validity.values()).count(Bigchain.BLOCK_VALID) > 1:
+                block_ids = str([block for block in validity
+                                       if validity[block] == Bigchain.BLOCK_VALID])
+                raise Exception('Transaction {tx} is present in multiple valid blocks: {block_ids}'
+                                .format(tx=txid, block_ids=block_ids))
+
+            return validity
 
-        # transaction ids should be unique
-        transactions = list(response)
-        if transactions:
-            if len(transactions) != 1:
-                raise Exception('Transaction ids should be unique. There is a problem with the chain')
-            else:
-                return transactions[0]
         else:
             return None
 
@@ -208,14 +268,25 @@ class Bigchain(object):
                     .contains(lambda fulfillment: fulfillment['input'] == tx_input))\
             .run(self.conn)
 
-        # a transaction_id should have been spent at most one time
         transactions = list(response)
+
+        # a transaction_id should have been spent at most one time
         if transactions:
-            if len(transactions) != 1:
+            # determine if these valid transactions appear in more than one valid block
-                raise exceptions.DoubleSpend('`{}` was spent more then once. There is a problem with the chain'.format(
+            num_valid_transactions = 0
-                    tx_input['txid']))
+            for transaction in transactions:
-            else:
+                # ignore invalid blocks
+                if self.get_transaction(transaction['id']):
+                    num_valid_transactions += 1
+                if num_valid_transactions > 1:
+                    raise exceptions.DoubleSpend('`{}` was spent more then once. There is a problem with the chain'.format(
+                        tx_input['txid']))
+
+            if num_valid_transactions:
                 return transactions[0]
+            else:
+                # all queried transactions were invalid
+                return None
         else:
             return None
 
@@ -239,6 +310,12 @@ class Bigchain(object):
         owned = []
 
         for tx in response:
+            # disregard transactions from invalid blocks
+            validity = self.get_blocks_status_containing_tx(tx['id'])
+            if Bigchain.BLOCK_VALID not in validity.values():
+                if Bigchain.BLOCK_UNDECIDED not in validity.values():
+                    continue
+
             # a transaction can contain multiple outputs (conditions) so we need to iterate over all of them
             # to get a list of outputs available to spend
             for condition in tx['transaction']['conditions']:
@@ -251,9 +328,8 @@ class Bigchain(object):
                     # for transactions with multiple `new_owners` there will be several subfulfillments nested
                     # in the condition. We need to iterate the subfulfillments to make sure there is a
                     # subfulfillment for `owner`
-                    for subfulfillment in condition['condition']['details']['subfulfillments']:
+                    if util.condition_details_has_owner(condition['condition']['details'], owner):
-                        if subfulfillment['public_key'] == owner:
+                        tx_input = {'txid': tx['id'], 'cid': condition['cid']}
-                            tx_input = {'txid': tx['id'], 'cid': condition['cid']}
                 # check if input was already spent
                 if not self.get_spent(tx_input):
                     owned.append(tx_input)
@@ -496,7 +572,7 @@ class Bigchain(object):
 
     def block_election_status(self, block):
         """Tally the votes on a block, and return the status: valid, invalid, or undecided."""
-        
+
         n_voters = len(block['block']['voters'])
         vote_cast = [vote['vote']['is_block_valid'] for vote in block['votes']]
         vote_validity = [self.consensus.verify_vote_signature(block, vote) for vote in block['votes']]

bigchaindb/util.py

@@ -447,7 +447,8 @@ def validate_fulfillments(signed_transaction):
             return False
 
         # TODO: might already break on a False here
-        is_valid = parsed_fulfillment.validate(serialize(fulfillment_message))
+        is_valid = parsed_fulfillment.validate(message=serialize(fulfillment_message),
+                                               now=timestamp())
 
         # if transaction has an input (i.e. not a `CREATE` transaction)
         # TODO: avoid instantiation, pass as argument!
@@ -525,6 +526,37 @@ def get_input_condition(bigchain, fulfillment):
         }
 
 
+def condition_details_has_owner(condition_details, owner):
+    """
+
+    Check if the public_key of owner is in the condition details
+    as an Ed25519Fulfillment.public_key
+
+    Args:
+        condition_details (dict): dict with condition details
+        owner (str): base58 public key of owner
+
+    Returns:
+        bool: True if the public key is found in the condition details, False otherwise
+
+    """
+    if 'subfulfillments' in condition_details:
+        result = condition_details_has_owner(condition_details['subfulfillments'], owner)
+        if result:
+            return True
+
+    elif isinstance(condition_details, list):
+        for subcondition in condition_details:
+            result = condition_details_has_owner(subcondition, owner)
+            if result:
+                return True
+    else:
+        if 'public_key' in condition_details \
+                and owner == condition_details['public_key']:
+            return True
+    return False
+
+
 def get_hash_data(transaction):
     """ Get the hashed data that (should) correspond to the `transaction['id']`
 

docs/source/models.md

@@ -6,47 +6,53 @@ Transactions, blocks and votes are represented using JSON documents with the fol
 
 ```json
 {
-    "id": "<sha3 hash>",
+    "id": "<SHA3-256 hash hexdigest of transaction (below)>",
-    "version": "<transaction version number>",
+    "version": "<version number of the transaction model>",
     "transaction": {
-        "fulfillments": ["<list of <fullfillment>"],
+        "fulfillments": ["<list of fulfillments>"],
-        "conditions": ["<list of <condition>"],
+        "conditions": ["<list of conditions>"],
         "operation": "<string>",
         "timestamp": "<timestamp from client>",
         "data": {
             "hash": "<SHA3-256 hash hexdigest of payload>",
-            "payload": "<generic json document>"
+            "payload": "<any JSON document>"
         }
     }
 }
 ```
 
-A transaction is an operation between the `current_owner` and the `new_owner` over the digital content described by `hash`. For example if could be a transfer of ownership of the digital content `hash`
+Transactions are the basic records stored by BigchainDB. There are two kinds:
 
-- **Transaction header**:
+1. A "CREATE" transaction creates a new asset. It has `"operation": "CREATE"`. The `payload` or a "CREATE" transaction describes, encodes, or links to the asset in some way.
-    - `id`: sha3 hash of the transaction. The `id` is also the DB primary key.
+2. A "TRANSFER" transaction transfers one or more assets. It has `"operation": "TRANSFER"`. The `payload` of a "TRANSFER" transaction can be empty, but it can also be used for use-case-specific information (e.g. different kinds of transfers).
-    - `version`: Version of the transaction. For future compability with changes in the transaction model.
+
-- **Transaction body**:
+Here's some explanation of the contents of a transaction:
-    - `fulfillments`: List of fulfillments. Each _fulfillment_ contains a pointer to an unspent digital asset
+
-    and a _crypto fulfillment_ that satisfies a spending condition set on the unspent digital asset. A _fulfillment_
+- `id`: The SHA3-256 hash hexdigest of everything inside the serialized `transaction` body (i.e. `fulfillments`, `conditions`, `operation`, `timestamp` and `data`; see below). The `id` is also the database primary key.
-    is usually a signature proving the ownership of the digital asset.
+- `version`: Version number of the transaction model, so that software can support different transaction models.
-    See [conditions and fulfillments](models.md#conditions-and-fulfillments)
+- `transaction`:
+    - `fulfillments`: List of fulfillments. Each _fulfillment_ contains a pointer to an unspent asset
+    and a _crypto fulfillment_ that satisfies a spending condition set on the unspent asset. A _fulfillment_
+    is usually a signature proving the ownership of the asset.
+    See [Conditions and Fulfillments](#conditions-and-fulfillments) below.
     - `conditions`: List of conditions. Each _condition_ is a _crypto condition_ that needs to be fulfilled by the
-    new owner in order to spend the digital asset.
+    new owner in order to spend the asset.
-    See [conditions and fulfillments](models.md#conditions-and-fulfillments)
+    See [Conditions and Fulfillments](#conditions-and-fulfillments) below.
-    - `operation`: String representation of the operation being performed (`CREATE`, `TRANSFER`, ...) this will define how
+    - `operation`: String representation of the operation being performed (currently either "CREATE" or "TRANSFER"). It determines how
-    the transactions should be validated
+    the transaction should be validated.
     - `timestamp`: Time of creation of the transaction in UTC. It's provided by the client.
-    - `data`: JSON object describing the asset (digital content). It contains at least the field `hash` which is a
+    - `data`:
-    sha3 hash of the digital content.
+        - `hash`: The SHA3-256 hash hexdigest of the serialized `payload`.
+        - `payload`: Can be any JSON document. Its meaning depends on the whether the transaction 
+    is a "CREATE" or "TRANSFER" transaction; see above.
 
 ## Conditions and Fulfillments
 
 ### Conditions
 
-##### Simple Signature
+#### One New Owner
 
-If there is only one _new owner_ the condition will be a single signature condition.
+If there is only one _new owner_, the condition will be a single-signature condition.
 
 ```json
 {
@@ -54,33 +60,32 @@ If there is only one _new owner_ the condition will be a single signature condit
     "condition": {
         "details": {
             "bitmask": "<base16 int>",
-            "public_key": "<explain>",
+            "public_key": "<new owner public key>",
             "signature": null,
             "type": "fulfillment",
             "type_id": "<base16 int>"
         },
         "uri": "<string>"
     },
-    "new_owners": ["<list of <base58 string>>"]
+    "new_owners": ["<new owner public key>"]
 }
 ```
 
 - **Condition header**:
     - `cid`: Condition index so that we can reference this output as an input to another transaction. It also matches
-    the input `fid`, making this the condition to fulfill in order to spend the digital asset used as input with `fid`
+    the input `fid`, making this the condition to fulfill in order to spend the asset used as input with `fid`.
-    - `new_owners`: List of public keys of the new owners.
+    - `new_owners`: A list containing one item: the public key of the new owner.
 - **Condition body**:
-    - `bitmask`: a set of bits representing the features required by the condition type
+    - `bitmask`: A set of bits representing the features required by the condition type.
-    - `public_key`: the base58 representation of the _new_owner's_ verifying key.
+    - `public_key`: The _new_owner's_ public key.
-    - `type_id`: the fulfillment type ID (see the [ILP spec](https://interledger.org/five-bells-condition/spec.html))
+    - `type_id`: The fulfillment type ID; see the [ILP spec](https://interledger.org/five-bells-condition/spec.html).
-    - `uri`: binary representation of the condition using only URL-safe characters
+    - `uri`: Binary representation of the condition using only URL-safe characters.
 
-##### Multi Signature
+#### Multiple New Owners
 
-If there are multiple _new owners_ by default we create a condition requiring a signature from each new owner in order
+If there are multiple _new owners_, we can create a ThresholdCondition requiring a signature from each new owner in order
-to spend the digital asset.
+to spend the asset. For example:
 
-Example of a condition with two _new owners_:
 ```json
 {
     "cid": "<condition index>",
@@ -121,16 +126,17 @@ Example of a condition with two _new owners_:
     - `weight`: integer weight for each subfulfillment's contribution to the threshold
 - `threshold`: threshold to reach for the subfulfillments to reach a valid fulfillment 
 
+The `weight`s and `threshold` could be adjusted. For example, if the `threshold` was changed to 1 above, then only one of the new owners would have to provide a signature to spend the asset.
 
 ### Fulfillments
 
-##### Simple Signature
+#### One Current Owner
 
-If there is only one _current owner_ the fulfillment will be a single signature fulfillment.
+If there is only one _current owner_, the fulfillment will be a single-signature fulfillment.
 
 ```json
 {
-    "current_owners": ["<Public Key>"],
+    "current_owners": ["<public key of current owner>"],
     "fid": 0,
     "fulfillment": "cf:4:RxFzIE679tFBk8zwEgizhmTuciAylvTUwy6EL6ehddHFJOhK5F4IjwQ1xLu2oQK9iyRCZJdfWAefZVjTt3DeG5j2exqxpGliOPYseNkRAWEakqJ_UrCwgnj92dnFRAEE",
     "input": {
@@ -140,11 +146,11 @@ If there is only one _current owner_ the fulfillment will be a single signature
 }
 ```
 
-- `fid`: Fulfillment index. It matches a `cid` in the conditions with a new _crypto condition_ that the new owner(s)
+- `fid`: Fulfillment index. It matches a `cid` in the conditions with a new _crypto condition_ that the new owner
-need to fulfill to spend this digital asset
+  needs to fulfill to spend this asset.
-- `current_owners`: Public key of the current owner(s)
+- `current_owners`: A list of public keys of the current owners; in this case it has just one public key.
-- `fulfillment`:
+- `fulfillment`: A cryptoconditions URI that encodes the cryptographic fulfillments like signatures and others, see crypto-conditions.
-- `input`: Pointer to the digital asset and condition of a previous transaction
+- `input`: Pointer to the asset and condition of a previous transaction
     - `cid`: Condition index
     - `txid`: Transaction id
 
@@ -152,7 +158,7 @@ need to fulfill to spend this digital asset
 
 ```json
 {
-    "id": "<sha3 hash of the serialized block contents>",
+    "id": "<SHA3-256 hash hexdigest of the serialized block contents>",
     "block": {
         "timestamp": "<block-creation timestamp>",
         "transactions": ["<list of transactions>"],
@@ -164,21 +170,16 @@ need to fulfill to spend this digital asset
 }
 ```
 
-Still to be defined when new blocks are created (after x number of transactions, or after x amount of seconds, 
+- `id`: SHA3-256 hash hexdigest of the contents of `block` (i.e. the timestamp, list of transactions, node_pubkey, and voters). This is also a database primary key; that's how we ensure that all blocks are unique.
-or both).
+- `block`:
-
+    - `timestamp`: Timestamp when the block was created. It's provided by the node that created the block.
-A block contains a group of transactions and includes the hash of the hash of the previous block to build the chain.
+    - `transactions`: A list of the transactions included in the block.
-
+    - `node_pubkey`: The public key of the node that create the block.
-- `id`: sha3 hash of the contents of `block` (i.e. the timestamp, list of transactions, node_pubkey, and voters). This is also a RethinkDB primary key; that's how we ensure that all blocks are unique.
+    - `voters`: A list of public keys of federation nodes. Since the size of the 
-- `block`: The actual block
+      federation may change over time, this will tell us how many nodes existed
-    - `timestamp`: timestamp when the block was created. It's provided by the node that created the block.
+      in the federation when the block was created, so that at a later point in
-    - `transactions`: the list of transactions included in the block
-    - `node_pubkey`: the public key of the node that create the block
-    - `voters`: list of public keys of the federation nodes. Since the size of the 
-      federation may change over time this will tell us how many nodes existed
-      in the federation when the block was created so that at a later point in
       time we can check that the block received the correct number of votes.
-- `signature`: Signature of the block by the node that created the block (i.e. To create it, the node serialized the block contents and signed that with its private key)
+- `signature`: Signature of the block by the node that created the block. (To create the signature, the node serializes the block contents and signs that with its private key.)
 - `votes`: Initially an empty list. New votes are appended as they come in from the nodes.
 
 ## The Vote Model
@@ -187,7 +188,7 @@ Each node must generate a vote for each block, to be appended to that block's `v
 
 ```json
 {
-    "node_pubkey": "<the pubkey of the voting node>",
+    "node_pubkey": "<the public key of the voting node>",
     "vote": {
         "voting_for_block": "<id of the block the node is voting for>",
         "previous_block": "<id of the block previous to this one>",
@@ -199,4 +200,4 @@ Each node must generate a vote for each block, to be appended to that block's `v
 }
 ```
 
-Note: The `invalid_reason` was not being used as of v0.1.3.
+Note: The `invalid_reason` was not being used as of v0.1.3 and may be dropped in a future version of BigchainDB.

docs/source/python-server-api-examples.md

@@ -129,7 +129,9 @@ The locking script is refered to as a `condition` and a corresponding `fulfillme
 
 Since a transaction can have multiple outputs with each its own (crypto)condition, each transaction input should also refer to the condition index `cid`.
 
-![BigchainDB transactions connecting fulfillments with conditions](./_static/tx_single_condition_single_fulfillment_v1.png)
+<p align="center">
+  <img width="70%" height="70%" src ="./_static/tx_single_condition_single_fulfillment_v1.png" />
+</p>
 
 
 ```python
@@ -379,7 +381,9 @@ With BigchainDB it is possible to send multiple assets to someone in a single tr
 
 The transaction will create a `fulfillment` - `condition` pair for each input, which can be refered to by `fid` and `cid` respectively.
 
-![BigchainDB transactions connecting multiple fulfillments with multiple conditions](./_static/tx_multi_condition_multi_fulfillment_v1.png)
+<p align="center">
+  <img width="70%" height="70%" src ="./_static/tx_multi_condition_multi_fulfillment_v1.png" />
+</p>
 
 ```python
 # Create some assets for bulk transfer
@@ -782,7 +786,6 @@ hashlock_tx_signed = b.sign_transaction(hashlock_tx, b.me_private)
 
 # Some validations
 assert b.validate_transaction(hashlock_tx_signed) == hashlock_tx_signed
-assert b.is_valid_transaction(hashlock_tx_signed) == hashlock_tx_signed
 
 b.write_transaction(hashlock_tx_signed)
 hashlock_tx_signed
@@ -840,7 +843,6 @@ hashlock_fulfill_tx['transaction']['fulfillments'][0]['fulfillment'] = \
     hashlock_fulfill_tx_fulfillment.serialize_uri()
 
 assert b.validate_transaction(hashlock_fulfill_tx) == hashlock_fulfill_tx
-assert b.is_valid_transaction(hashlock_fulfill_tx) == hashlock_fulfill_tx
 
 b.write_transaction(hashlock_fulfill_tx)
 hashlock_fulfill_tx
@@ -885,4 +887,416 @@ hashlock_fulfill_tx
     },
     "version":1
 }
-```
+```
+
+### Timeout Conditions
+
+Timeout conditions allow assets to expire after a certain time.
+The primary use case of timeout conditions is to enable [Escrow](#escrow).
+
+The condition can only be fulfilled before the expiry time. 
+Once expired, the asset is lost and cannot be fulfilled by anyone.
+
+__Note__: The timeout conditions are BigchainDB-specific and not (yet) supported by the ILP standard.
+
+__Caveat__: The times between nodes in a BigchainDB federation may (and will) differ slightly. In this case, the majority of the nodes will decide.
+
+```python
+# Create a timeout asset without any new_owners
+tx_timeout = b.create_transaction(b.me, None, None, 'CREATE')
+
+# Set expiry time - the asset needs to be transfered before expiration
+time_sleep = 12
+time_expire = str(float(util.timestamp()) + time_sleep)  # 12 secs from now
+condition_timeout = cc.TimeoutFulfillment(expire_time=time_expire)
+
+# The conditions list is empty, so we need to append a new condition
+tx_timeout['transaction']['conditions'].append({
+    'condition': {
+        'details': json.loads(condition_timeout.serialize_json()),
+        'uri': condition_timeout.condition.serialize_uri()
+    },
+    'cid': 0,
+    'new_owners': None
+})
+
+# Conditions have been updated, so the hash needs updating
+tx_timeout['id'] = util.get_hash_data(tx_timeout)
+
+# The asset needs to be signed by the current_owner
+tx_timeout_signed = b.sign_transaction(tx_timeout, b.me_private)
+
+# Some validations
+assert b.validate_transaction(tx_timeout_signed) == tx_timeout_signed
+
+b.write_transaction(tx_timeout_signed)
+tx_timeout_signed
+```
+
+```python
+{
+    "id":"78145396cd368f7168fb01c97aaf1df6f85244d7b544073dfcb42397dae38f90",
+    "transaction":{
+        "conditions":[
+            {
+                "cid":0,
+                "condition":{
+                    "details":{
+                        "bitmask":9,
+                        "expire_time":"1464167910.643431",
+                        "type":"fulfillment",
+                        "type_id":99
+                    },
+                    "uri":"cc:63:9:sceU_NZc3cAjAvaR1TVmgj7am5y8hJEBoqLm-tbqGbQ:17"
+                },
+                "new_owners":null
+            }
+        ],
+        "data":null,
+        "fulfillments":[
+            {
+                "current_owners":[
+                    "FmLm6MxCABc8TsiZKdeYaZKo5yZWMM6Vty7Q1B6EgcP2"
+                ],
+                "fid":0,
+                "fulfillment":null,
+                "input":null
+            }
+        ],
+        "operation":"CREATE",
+        "timestamp":"1464167898.643353"
+    },
+    "version":1
+}
+```
+
+The following demonstrates that the transaction invalidates once the timeout occurs:
+
+```python
+from time import sleep
+
+# Create a timeout fulfillment tx
+tx_timeout_transfer = b.create_transaction(None, testuser1_pub, {'txid': tx_timeout['id'], 'cid': 0}, 'TRANSFER')
+
+# Parse the timeout condition and create the corresponding fulfillment
+timeout_fulfillment = cc.Fulfillment.from_json(
+    tx_timeout['transaction']['conditions'][0]['condition']['details'])
+tx_timeout_transfer['transaction']['fulfillments'][0]['fulfillment'] = timeout_fulfillment.serialize_uri()
+
+# No need to sign transaction, like with hashlocks
+
+# Small test to see the state change
+for i in range(time_sleep - 4):
+    tx_timeout_valid = b.is_valid_transaction(tx_timeout_transfer) == tx_timeout_transfer
+    seconds_to_timeout = int(float(time_expire) - float(util.timestamp()))
+    print('tx_timeout valid: {} ({}s to timeout)'.format(tx_timeout_valid, seconds_to_timeout))
+    sleep(1)
+```
+
+If you were fast enough, you should see the following output:
+
+```python
+tx_timeout valid: True (3s to timeout)
+tx_timeout valid: True (2s to timeout)
+tx_timeout valid: True (1s to timeout)
+tx_timeout valid: True (0s to timeout)
+tx_timeout valid: False (0s to timeout)
+tx_timeout valid: False (-1s to timeout)
+tx_timeout valid: False (-2s to timeout)
+tx_timeout valid: False (-3s to timeout)
+```
+
+## Escrow
+
+Escrow is a mechanism for conditional release of assets.
+
+This means that a the assets are locked up by a trusted party until an `execute` condition is presented. In order not to tie up the assets forever, the escrow foresees an `abort` condition, which is typically an expiry time.
+
+BigchainDB and cryptoconditions provides escrow out-of-the-box, without the need of a trusted party.
+
+A threshold condition is used to represent the escrow, since BigchainDB transactions cannot have a _pending_ state.
+
+<p align="center">
+  <img width="70%" height="70%" src ="./_static/tx_escrow_execute_abort.png" />
+</p>
+
+The logic for switching between `execute` and `abort` conditions is conceptually simple:
+
+```python
+if timeout_condition.validate(utcnow()):
+    execute_fulfillment.validate(msg) == True
+    abort_fulfillment.validate(msg) == False
+else:
+    execute_fulfillment.validate(msg) == False
+    abort_fulfillment.validate(msg) == True
+```
+
+The above switch can be implemented as follows using threshold cryptoconditions:
+
+<p align="center">
+  <img width="100%" height="100%" src ="./_static/cc_escrow_execute_abort.png" />
+</p>
+
+The small circle (&#9898;) at an input of a threshold condition denotes an inversion of the fulfillment:
+
+```python
+inverted_fulfillment.validate(msg) == not fulfillment.validate(msg)
+```
+
+An inverted input to a threshold condition is simply obtained by negative weights.
+
+__Note__: negative weights are BigchainDB-specific and not (yet) supported by the ILP standard.
+
+
+The following code snippet shows how to create an escrow condition:
+
+```python
+# Retrieve the last transaction of testuser2_pub (or create a new asset)
+tx_retrieved_id = b.get_owned_ids(testuser2_pub).pop()
+
+# Create a base template with the execute and abort address
+tx_escrow = b.create_transaction(testuser2_pub, [testuser2_pub, testuser1_pub], tx_retrieved_id, 'TRANSFER')
+
+# Set expiry time - the execute address needs to fulfill before expiration 
+time_sleep = 12
+time_expire = str(float(util.timestamp()) + time_sleep)  # 12 secs from now
+
+# Create the escrow and timeout condition
+condition_escrow = cc.ThresholdSha256Fulfillment(threshold=1)  # OR Gate
+condition_timeout = cc.TimeoutFulfillment(expire_time=time_expire)  # only valid if now() <= time_expire
+
+# Create the execute branch
+condition_execute = cc.ThresholdSha256Fulfillment(threshold=2)  # AND gate
+condition_execute.add_subfulfillment(cc.Ed25519Fulfillment(public_key=testuser1_pub))  # execute address
+condition_execute.add_subfulfillment(condition_timeout)  # federation checks on expiry
+condition_escrow.add_subfulfillment(condition_execute)
+
+# Create the abort branch
+condition_abort = cc.ThresholdSha256Fulfillment(threshold=2)  # AND gate
+condition_abort.add_subfulfillment(cc.Ed25519Fulfillment(public_key=testuser2_pub))  # abort address
+condition_abort.add_subfulfillment(condition_timeout, weight=-1)  # the negative weight inverts the condition
+condition_escrow.add_subfulfillment(condition_abort)
+
+# Update the condition in the newly created transaction
+tx_escrow['transaction']['conditions'][0]['condition'] = {
+    'details': json.loads(condition_escrow.serialize_json()),
+    'uri': condition_escrow.condition.serialize_uri()
+}
+
+# Conditions have been updated, so the hash needs updating
+tx_escrow['id'] = util.get_hash_data(tx_escrow)
+
+# The asset needs to be signed by the current_owner
+tx_escrow_signed = b.sign_transaction(tx_escrow, testuser2_priv)
+
+# Some validations
+assert b.validate_transaction(tx_escrow_signed) == tx_escrow_signed
+
+b.write_transaction(tx_escrow_signed)
+tx_escrow_signed
+```
+
+```python
+{
+    "id":"1a281da2b9bc3d2beba92479058d440de3353427fd64045a61737bad0d0c809c",
+    "transaction":{
+        "conditions":[
+            {
+                "cid":0,
+                "condition":{
+                    "details":{
+                        "bitmask":41,
+                        "subfulfillments":[
+                            {
+                                "bitmask":41,
+                                "subfulfillments":[
+                                    {
+                                        "bitmask":32,
+                                        "public_key":"qv8DvdNG5nZHWCP5aPSqgqxAvaPJpQj19abRvFCntor",
+                                        "signature":null,
+                                        "type":"fulfillment",
+                                        "type_id":4,
+                                        "weight":1
+                                    },
+                                    {
+                                        "bitmask":9,
+                                        "expire_time":"1464242352.227917",
+                                        "type":"fulfillment",
+                                        "type_id":99,
+                                        "weight":1
+                                    }
+                                ],
+                                "threshold":2,
+                                "type":"fulfillment",
+                                "type_id":2,
+                                "weight":1
+                            },
+                            {
+                                "bitmask":41,
+                                "subfulfillments":[
+                                    {
+                                        "bitmask":32,
+                                        "public_key":"BwuhqQX8FPsmqYiRV2CSZYWWsSWgSSQQFHjqxKEuqkPs",
+                                        "signature":null,
+                                        "type":"fulfillment",
+                                        "type_id":4,
+                                        "weight":1
+                                    },
+                                    {
+                                        "bitmask":9,
+                                        "expire_time":"1464242352.227917",
+                                        "type":"fulfillment",
+                                        "type_id":99,
+                                        "weight":-1
+                                    }
+                                ],
+                                "threshold":2,
+                                "type":"fulfillment",
+                                "type_id":2,
+                                "weight":1
+                            }
+                        ],
+                        "threshold":1,
+                        "type":"fulfillment",
+                        "type_id":2
+                    },
+                    "uri":"cc:2:29:sg08ERtppQrGxot7mu7XMdNkZTc29xCbWE1r8DgxuL8:181"
+                },
+                "new_owners":[
+                    "BwuhqQX8FPsmqYiRV2CSZYWWsSWgSSQQFHjqxKEuqkPs",
+                    "qv8DvdNG5nZHWCP5aPSqgqxAvaPJpQj19abRvFCntor"
+                ]
+            }
+        ],
+        "data":null,
+        "fulfillments":[
+            {
+                "current_owners":[
+                    "qv8DvdNG5nZHWCP5aPSqgqxAvaPJpQj19abRvFCntor"
+                ],
+                "fid":0,
+                "fulfillment":"cf:4:B6VAa7KAMD1v-pyvDx9RuBLb6l2Qs3vhucgXqzU_RbuRucOp6tNY8AoNMoC-HAOZBJSnHXZsdJ7pLCZ6aDTwUHXf0zxyLaCgy1NpES3h8qcuxbfv4Nchw3BtUcVSY3AM",
+                "input":{
+                    "cid":1,
+                    "txid":"d3f5e78f6d4346466178745f1c01cbcaf1c1dce1932a16cd653051b16ee29bac"
+                }
+            }
+        ],
+        "operation":"TRANSFER",
+        "timestamp":"1464242340.227787"
+    },
+    "version":1
+}
+```
+
+At any given moment `testuser1` and `testuser2` can try to fulfill the `execute` and `abort` branch respectively.
+Whether the fulfillment will validate depends on the timeout condition.
+
+We'll illustrate this by example.
+
+In the case of `testuser1`, we create the `execute` fulfillment:
+
+```python
+# Create a base template for execute fulfillment
+tx_escrow_execute = b.create_transaction([testuser2_pub, testuser1_pub], testuser1_pub, {'txid': tx_escrow_signed['id'], 'cid': 0}, 'TRANSFER')
+
+# Parse the Escrow cryptocondition
+escrow_fulfillment = cc.Fulfillment.from_json(
+    tx_escrow['transaction']['conditions'][0]['condition']['details'])
+
+subfulfillment_testuser1 = escrow_fulfillment.get_subcondition_from_vk(testuser1_pub)[0]
+subfulfillment_testuser2 = escrow_fulfillment.get_subcondition_from_vk(testuser2_pub)[0]
+subfulfillment_timeout = escrow_fulfillment.subconditions[0]['body'].subconditions[1]['body']
+
+# Get the fulfillment message to sign
+tx_escrow_execute_fulfillment_message = \
+    util.get_fulfillment_message(tx_escrow_execute,
+                                 tx_escrow_execute['transaction']['fulfillments'][0],
+                                 serialized=True)
+
+# Clear the subconditions of the escrow fulfillment
+escrow_fulfillment.subconditions = []
+
+# Fulfill the execute branch
+fulfillment_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+subfulfillment_testuser1.sign(tx_escrow_execute_fulfillment_message, crypto.SigningKey(testuser1_priv))
+fulfillment_execute.add_subfulfillment(subfulfillment_testuser1)
+fulfillment_execute.add_subfulfillment(subfulfillment_timeout)
+escrow_fulfillment.add_subfulfillment(fulfillment_execute)
+
+# Do not fulfill the abort branch
+condition_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+condition_abort.add_subfulfillment(subfulfillment_testuser2)
+condition_abort.add_subfulfillment(subfulfillment_timeout, weight=-1)
+escrow_fulfillment.add_subcondition(condition_abort.condition)  # Adding only the condition here
+
+# Update the execute transaction with the fulfillment
+tx_escrow_execute['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+```
+
+In the case of `testuser2`, we create the `abort` fulfillment:
+
+```python
+# Create a base template for execute fulfillment
+tx_escrow_abort = b.create_transaction([testuser2_pub, testuser1_pub], testuser2_pub, {'txid': tx_escrow_signed['id'], 'cid': 0}, 'TRANSFER')
+
+# Parse the threshold cryptocondition
+escrow_fulfillment = cc.Fulfillment.from_json(
+    tx_escrow['transaction']['conditions'][0]['condition']['details'])
+
+subfulfillment_testuser1 = escrow_fulfillment.get_subcondition_from_vk(testuser1_pub)[0]
+subfulfillment_testuser2 = escrow_fulfillment.get_subcondition_from_vk(testuser2_pub)[0]
+subfulfillment_timeout = escrow_fulfillment.subconditions[0]['body'].subconditions[1]['body']
+
+# Get the fulfillment message to sign
+tx_escrow_abort_fulfillment_message = \
+    util.get_fulfillment_message(tx_escrow_abort,
+                                 tx_escrow_abort['transaction']['fulfillments'][0],
+                                 serialized=True)
+                                 
+# Clear the subconditions of the escrow fulfillment
+escrow_fulfillment.subconditions = []
+
+# Do not fulfill the execute branch
+condition_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+condition_execute.add_subfulfillment(subfulfillment_testuser1)
+condition_execute.add_subfulfillment(subfulfillment_timeout)
+escrow_fulfillment.add_subcondition(condition_execute.condition) # Adding only the condition here
+
+# Fulfill the abort branch
+fulfillment_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+subfulfillment_testuser2.sign(tx_escrow_abort_fulfillment_message, crypto.SigningKey(testuser2_priv))
+fulfillment_abort.add_subfulfillment(subfulfillment_testuser2)
+fulfillment_abort.add_subfulfillment(subfulfillment_timeout, weight=-1)
+escrow_fulfillment.add_subfulfillment(fulfillment_abort)
+
+# Update the abort transaction with the fulfillment
+tx_escrow_abort['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+```
+
+The following demonstrates that the transaction validation switches once the timeout occurs:
+
+```python
+for i in range(time_sleep - 4):
+    valid_execute = b.is_valid_transaction(tx_escrow_execute) == tx_escrow_execute
+    valid_abort = b.is_valid_transaction(tx_escrow_abort) == tx_escrow_abort
+
+    seconds_to_timeout = int(float(time_expire) - float(util.timestamp()))
+    print('tx_execute valid: {} - tx_abort valid {} ({}s to timeout)'.format(valid_execute, valid_abort, seconds_to_timeout))
+    sleep(1)
+```
+
+If you execute in a timely fashion, you should see the following:
+
+```python
+tx_execute valid: True - tx_abort valid False (3s to timeout)
+tx_execute valid: True - tx_abort valid False (2s to timeout)
+tx_execute valid: True - tx_abort valid False (1s to timeout)
+tx_execute valid: True - tx_abort valid False (0s to timeout)
+tx_execute valid: False - tx_abort valid True (0s to timeout)
+tx_execute valid: False - tx_abort valid True (-1s to timeout)
+tx_execute valid: False - tx_abort valid True (-2s to timeout)
+tx_execute valid: False - tx_abort valid True (-3s to timeout)
+```
+
+Of course, when the `execute` transaction was accepted in-time by bigchaindb, then writing the `abort` transaction after expiry will yield a `Doublespend` error.

setup.py

@@ -96,7 +96,7 @@ setup(
         'rethinkdb==2.3.0',
         'pysha3==0.3',
         'pytz==2015.7',
-        'cryptoconditions==0.2.2',
+        'cryptoconditions==0.3.0',
         'statsd==3.2.1',
         'python-rapidjson==0.0.6',
         'logstats==0.2.1',

tests/db/conftest.py

@@ -50,6 +50,11 @@ def setup_database(request, node_config):
     r.db(db_name).table('backlog')\
         .index_create('assignee__transaction_timestamp', [r.row['assignee'], r.row['transaction']['timestamp']])\
         .run()
+    # order transactions by id
+    r.db(db_name).table('bigchain').index_create('transaction_id', r.row['block']['transactions']['id'],
+                                                 multi=True).run()
+
+    r.db(db_name).table('bigchain').index_wait('transaction_id').run()
 
     def fin():
         print('Deleting `{}` database'.format(db_name))

tests/db/test_bigchain_api.py

@@ -107,6 +107,25 @@ class TestBigchainApi(object):
         response = b.get_transaction(tx_signed["id"])
         assert util.serialize(tx_signed) == util.serialize(response)
 
+    @pytest.mark.usefixtures('inputs')
+    def test_read_transaction_invalid_block(self, b, user_vk, user_sk):
+        input_tx = b.get_owned_ids(user_vk).pop()
+        tx = b.create_transaction(user_vk, user_vk, input_tx, 'TRANSFER')
+        tx_signed = b.sign_transaction(tx, user_sk)
+        b.write_transaction(tx_signed)
+
+        # create block
+        block = b.create_block([tx_signed])
+        b.write_block(block, durability='hard')
+
+        # vote the block invalid
+        vote = b.vote(block, b.get_last_voted_block()['id'], False)
+        b.write_vote(block, vote, 3)
+        response = b.get_transaction(tx_signed["id"])
+
+        # should be None, because invalid blocks are ignored
+        assert response is None
+
     @pytest.mark.usefixtures('inputs')
     def test_assign_transaction_one_node(self, b, user_vk, user_sk):
         input_tx = b.get_owned_ids(user_vk).pop()
@@ -1033,6 +1052,43 @@ class TestMultipleInputs(object):
         assert owned_inputs_user1 == []
         assert owned_inputs_user2 == [{'cid': 0, 'txid': tx['id']}]
 
+    def test_get_owned_ids_single_tx_single_output_invalid_block(self, b, user_sk, user_vk):
+        # create a new users
+        user2_sk, user2_vk = crypto.generate_key_pair()
+
+        # create input to spend
+        tx = b.create_transaction(b.me, user_vk, None, 'CREATE')
+        tx_signed = b.sign_transaction(tx, b.me_private)
+        block = b.create_block([tx_signed])
+        b.write_block(block, durability='hard')
+
+        # vote the block VALID
+        vote = b.vote(block, b.get_unvoted_blocks()[0]['id'], True)
+        b.write_vote(block, vote, 2)
+
+        # get input
+        owned_inputs_user1 = b.get_owned_ids(user_vk)
+        owned_inputs_user2 = b.get_owned_ids(user2_vk)
+        assert owned_inputs_user1 == [{'cid': 0, 'txid': tx['id']}]
+        assert owned_inputs_user2 == []
+
+        # create a transaction and block
+        tx_invalid = b.create_transaction(user_vk, user2_vk, owned_inputs_user1, 'TRANSFER')
+        tx_invalid_signed = b.sign_transaction(tx_invalid, user_sk)
+        block = b.create_block([tx_invalid_signed])
+        b.write_block(block, durability='hard')
+
+        # vote the block invalid
+        vote = b.vote(block, b.get_last_voted_block()['id'], False)
+        b.write_vote(block, vote, 3)
+
+        owned_inputs_user1 = b.get_owned_ids(user_vk)
+        owned_inputs_user2 = b.get_owned_ids(user2_vk)
+
+        # should be the same as before (note tx, not tx_invalid)
+        assert owned_inputs_user1 == [{'cid': 0, 'txid': tx['id']}]
+        assert owned_inputs_user2 == []
+
     def test_get_owned_ids_single_tx_multiple_outputs(self, b, user_sk, user_vk):
         # create a new users
         user2_sk, user2_vk = crypto.generate_key_pair()
@@ -1124,6 +1180,42 @@ class TestMultipleInputs(object):
         spent_inputs_user1 = b.get_spent(owned_inputs_user1[0])
         assert spent_inputs_user1 == tx_signed
 
+    def test_get_spent_single_tx_single_output_invalid_block(self, b, user_sk, user_vk):
+        # create a new users
+        user2_sk, user2_vk = crypto.generate_key_pair()
+
+        # create input to spend
+        tx = b.create_transaction(b.me, user_vk, None, 'CREATE')
+        tx_signed = b.sign_transaction(tx, b.me_private)
+        block = b.create_block([tx_signed])
+        b.write_block(block, durability='hard')
+
+        # vote the block VALID
+        vote = b.vote(block, b.get_unvoted_blocks()[0]['id'], True)
+        b.write_vote(block, vote, 2)
+
+        # get input
+        owned_inputs_user1 = b.get_owned_ids(user_vk)
+
+        # check spents
+        spent_inputs_user1 = b.get_spent(owned_inputs_user1[0])
+        assert spent_inputs_user1 is None
+
+        # create a transaction and block
+        tx = b.create_transaction(user_vk, user2_vk, owned_inputs_user1, 'TRANSFER')
+        tx_signed = b.sign_transaction(tx, user_sk)
+        block = b.create_block([tx_signed])
+        b.write_block(block, durability='hard')
+
+        # vote the block invalid
+        vote = b.vote(block, b.get_last_voted_block()['id'], False)
+        b.write_vote(block, vote, 2)
+        response = b.get_transaction(tx_signed["id"])
+        spent_inputs_user1 = b.get_spent(owned_inputs_user1[0])
+
+        # Now there should be no spents (the block is invalid)
+        assert spent_inputs_user1 is None
+
     def test_get_spent_single_tx_multiple_outputs(self, b, user_sk, user_vk):
         # create a new users
         user2_sk, user2_vk = crypto.generate_key_pair()
@@ -1878,3 +1970,265 @@ class TestCryptoconditions(object):
         for new_owner in new_owners:
             subcondition = condition.get_subcondition_from_vk(new_owner)[0]
             assert subcondition.public_key.to_ascii().decode() == new_owner
+
+    @pytest.mark.usefixtures('inputs')
+    def test_transfer_asset_with_escrow_condition(self, b, user_vk, user_sk):
+        first_input_tx = b.get_owned_ids(user_vk).pop()
+        user2_sk, user2_vk = crypto.generate_key_pair()
+
+        # ESCROW
+        escrow_tx = b.create_transaction(user_vk, [user_vk, user2_vk], first_input_tx, 'TRANSFER')
+
+        time_sleep = 3
+
+        condition_escrow = cc.ThresholdSha256Fulfillment(threshold=1)
+        fulfillment_timeout = cc.TimeoutFulfillment(expire_time=str(float(util.timestamp()) + time_sleep))
+        condition_user = cc.Ed25519Fulfillment(public_key=user_vk)
+        condition_user2 = cc.Ed25519Fulfillment(public_key=user2_vk)
+
+        # execute branch
+        fulfillment_and_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_execute.add_subfulfillment(condition_user2)
+        fulfillment_and_execute.add_subfulfillment(fulfillment_timeout)
+
+        # do not fulfill abort branch
+        fulfillment_and_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_abort.add_subfulfillment(condition_user)
+        fulfillment_and_abort.add_subfulfillment(fulfillment_timeout, weight=-1)
+
+        condition_escrow.add_subfulfillment(fulfillment_and_execute)
+        condition_escrow.add_subfulfillment(fulfillment_and_abort)
+
+        # Update the condition in the newly created transaction
+        escrow_tx['transaction']['conditions'][0]['condition'] = {
+            'details': json.loads(condition_escrow.serialize_json()),
+            'uri': condition_escrow.condition.serialize_uri()
+        }
+
+        # conditions have been updated, so hash needs updating
+        escrow_tx['id'] = util.get_hash_data(escrow_tx)
+
+        escrow_tx_signed = b.sign_transaction(escrow_tx, user_sk)
+
+        assert b.validate_transaction(escrow_tx_signed) == escrow_tx_signed
+        assert b.is_valid_transaction(escrow_tx_signed) == escrow_tx_signed
+
+        b.write_transaction(escrow_tx_signed)
+
+        # create and write block to bigchain
+        block = b.create_block([escrow_tx_signed])
+        b.write_block(block, durability='hard')
+
+        # Retrieve the last transaction of thresholduser1_pub
+        tx_retrieved_id = b.get_owned_ids(user2_vk).pop()
+
+        # EXECUTE
+        # Create a base template for output transaction
+        escrow_tx_transfer = b.create_transaction([user_vk, user2_vk], user2_vk, tx_retrieved_id, 'TRANSFER')
+
+        # Parse the threshold cryptocondition
+        escrow_fulfillment = cc.Fulfillment.from_json(
+            escrow_tx['transaction']['conditions'][0]['condition']['details'])
+
+        subfulfillment_user = escrow_fulfillment.get_subcondition_from_vk(user_vk)[0]
+        subfulfillment_user2 = escrow_fulfillment.get_subcondition_from_vk(user2_vk)[0]
+
+        # Get the fulfillment message to sign
+        escrow_tx_fulfillment_message = util.get_fulfillment_message(escrow_tx_transfer,
+                                                                     escrow_tx_transfer['transaction']['fulfillments'][0],
+                                                                     serialized=True)
+        escrow_fulfillment.subconditions = []
+        # fulfill execute branch
+        fulfillment_and_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+        subfulfillment_user2.sign(escrow_tx_fulfillment_message, crypto.SigningKey(user2_sk))
+        fulfillment_and_execute.add_subfulfillment(subfulfillment_user2)
+        fulfillment_and_execute.add_subfulfillment(fulfillment_timeout)
+        escrow_fulfillment.add_subfulfillment(fulfillment_and_execute)
+
+        # do not fulfill abort branch
+        fulfillment_and_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_abort.add_subfulfillment(subfulfillment_user)
+        fulfillment_and_abort.add_subfulfillment(fulfillment_timeout, weight=-1)
+        escrow_fulfillment.add_subcondition(fulfillment_and_abort.condition)
+
+        escrow_tx_transfer['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+
+        # in-time validation (execute)
+        assert b.is_valid_transaction(escrow_tx_transfer) == escrow_tx_transfer
+        assert b.validate_transaction(escrow_tx_transfer) == escrow_tx_transfer
+
+        time.sleep(time_sleep)
+
+        assert b.is_valid_transaction(escrow_tx_transfer) is False
+        with pytest.raises(exceptions.InvalidSignature):
+            assert b.validate_transaction(escrow_tx_transfer) == escrow_tx_transfer
+
+        # ABORT
+        # Create a base template for output transaction
+        escrow_tx_abort = b.create_transaction([user_vk, user2_vk], user_vk, tx_retrieved_id, 'TRANSFER')
+
+        # Parse the threshold cryptocondition
+        escrow_fulfillment = cc.Fulfillment.from_json(
+            escrow_tx['transaction']['conditions'][0]['condition']['details'])
+
+        subfulfillment_user = escrow_fulfillment.get_subcondition_from_vk(user_vk)[0]
+        subfulfillment_user2 = escrow_fulfillment.get_subcondition_from_vk(user2_vk)[0]
+
+        # Get the fulfillment message to sign
+        escrow_tx_fulfillment_message = util.get_fulfillment_message(escrow_tx_abort,
+                                                                     escrow_tx_abort['transaction']['fulfillments'][0],
+                                                                     serialized=True)
+        escrow_fulfillment.subconditions = []
+        # fulfill execute branch
+        fulfillment_and_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_execute.add_subfulfillment(subfulfillment_user2)
+        fulfillment_and_execute.add_subfulfillment(fulfillment_timeout)
+        escrow_fulfillment.add_subcondition(fulfillment_and_execute.condition)
+
+        # do not fulfill abort branch
+        fulfillment_and_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+        subfulfillment_user.sign(escrow_tx_fulfillment_message, crypto.SigningKey(user_sk))
+        fulfillment_and_abort.add_subfulfillment(subfulfillment_user)
+        fulfillment_and_abort.add_subfulfillment(fulfillment_timeout, weight=-1)
+        escrow_fulfillment.add_subfulfillment(fulfillment_and_abort)
+
+        escrow_tx_abort['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+
+        # out-of-time validation (abort)
+        assert b.validate_transaction(escrow_tx_abort) == escrow_tx_abort
+        assert b.is_valid_transaction(escrow_tx_abort) == escrow_tx_abort
+
+    @pytest.mark.usefixtures('inputs')
+    def test_transfer_asset_with_escrow_condition_doublespend(self, b, user_vk, user_sk):
+        first_input_tx = b.get_owned_ids(user_vk).pop()
+        user2_sk, user2_vk = crypto.generate_key_pair()
+
+        # ESCROW
+        escrow_tx = b.create_transaction(user_vk, [user_vk, user2_vk], first_input_tx, 'TRANSFER')
+
+        time_sleep = 3
+
+        condition_escrow = cc.ThresholdSha256Fulfillment(threshold=1)
+        fulfillment_timeout = cc.TimeoutFulfillment(expire_time=str(float(util.timestamp()) + time_sleep))
+        condition_user = cc.Ed25519Fulfillment(public_key=user_vk)
+        condition_user2 = cc.Ed25519Fulfillment(public_key=user2_vk)
+
+        # execute branch
+        fulfillment_and_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_execute.add_subfulfillment(condition_user2)
+        fulfillment_and_execute.add_subfulfillment(fulfillment_timeout)
+
+        # do not fulfill abort branch
+        fulfillment_and_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_abort.add_subfulfillment(condition_user)
+        fulfillment_and_abort.add_subfulfillment(fulfillment_timeout, weight=-1)
+
+        condition_escrow.add_subfulfillment(fulfillment_and_execute)
+        condition_escrow.add_subfulfillment(fulfillment_and_abort)
+
+        # Update the condition in the newly created transaction
+        escrow_tx['transaction']['conditions'][0]['condition'] = {
+            'details': json.loads(condition_escrow.serialize_json()),
+            'uri': condition_escrow.condition.serialize_uri()
+        }
+
+        # conditions have been updated, so hash needs updating
+        escrow_tx['id'] = util.get_hash_data(escrow_tx)
+
+        escrow_tx_signed = b.sign_transaction(escrow_tx, user_sk)
+
+        assert b.validate_transaction(escrow_tx_signed) == escrow_tx_signed
+        assert b.is_valid_transaction(escrow_tx_signed) == escrow_tx_signed
+
+        b.write_transaction(escrow_tx_signed)
+
+        # create and write block to bigchain
+        block = b.create_block([escrow_tx_signed])
+        b.write_block(block, durability='hard')
+
+        # Retrieve the last transaction of thresholduser1_pub
+        tx_retrieved_id = b.get_owned_ids(user2_vk).pop()
+
+        # EXECUTE
+        # Create a base template for output transaction
+        escrow_tx_transfer = b.create_transaction([user_vk, user2_vk], user2_vk, tx_retrieved_id, 'TRANSFER')
+
+        # Parse the threshold cryptocondition
+        escrow_fulfillment = cc.Fulfillment.from_json(
+            escrow_tx['transaction']['conditions'][0]['condition']['details'])
+
+        subfulfillment_user = escrow_fulfillment.get_subcondition_from_vk(user_vk)[0]
+        subfulfillment_user2 = escrow_fulfillment.get_subcondition_from_vk(user2_vk)[0]
+
+        # Get the fulfillment message to sign
+        escrow_tx_fulfillment_message = util.get_fulfillment_message(escrow_tx_transfer,
+                                                                     escrow_tx_transfer['transaction']['fulfillments'][0],
+                                                                     serialized=True)
+        escrow_fulfillment.subconditions = []
+        # fulfill execute branch
+        fulfillment_and_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+        subfulfillment_user2.sign(escrow_tx_fulfillment_message, crypto.SigningKey(user2_sk))
+        fulfillment_and_execute.add_subfulfillment(subfulfillment_user2)
+        fulfillment_and_execute.add_subfulfillment(fulfillment_timeout)
+        escrow_fulfillment.add_subfulfillment(fulfillment_and_execute)
+
+        # do not fulfill abort branch
+        fulfillment_and_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_abort.add_subfulfillment(subfulfillment_user)
+        fulfillment_and_abort.add_subfulfillment(fulfillment_timeout, weight=-1)
+        escrow_fulfillment.add_subcondition(fulfillment_and_abort.condition)
+
+        escrow_tx_transfer['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+
+        # in-time validation (execute)
+        assert b.is_valid_transaction(escrow_tx_transfer) == escrow_tx_transfer
+        assert b.validate_transaction(escrow_tx_transfer) == escrow_tx_transfer
+
+        b.write_transaction(escrow_tx_transfer)
+
+        # create and write block to bigchain
+        block = b.create_block([escrow_tx_transfer])
+        b.write_block(block, durability='hard')
+
+        time.sleep(time_sleep)
+
+        assert b.is_valid_transaction(escrow_tx_transfer) is False
+        with pytest.raises(exceptions.InvalidSignature):
+            assert b.validate_transaction(escrow_tx_transfer) == escrow_tx_transfer
+
+        # ABORT
+        # Create a base template for output transaction
+        escrow_tx_abort = b.create_transaction([user_vk, user2_vk], user_vk, tx_retrieved_id, 'TRANSFER')
+
+        # Parse the threshold cryptocondition
+        escrow_fulfillment = cc.Fulfillment.from_json(
+            escrow_tx['transaction']['conditions'][0]['condition']['details'])
+
+        subfulfillment_user = escrow_fulfillment.get_subcondition_from_vk(user_vk)[0]
+        subfulfillment_user2 = escrow_fulfillment.get_subcondition_from_vk(user2_vk)[0]
+
+        # Get the fulfillment message to sign
+        escrow_tx_fulfillment_message = util.get_fulfillment_message(escrow_tx_abort,
+                                                                     escrow_tx_abort['transaction']['fulfillments'][0],
+                                                                     serialized=True)
+        escrow_fulfillment.subconditions = []
+        # do not fulfill execute branch
+        fulfillment_and_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+        fulfillment_and_execute.add_subfulfillment(subfulfillment_user2)
+        fulfillment_and_execute.add_subfulfillment(fulfillment_timeout)
+        escrow_fulfillment.add_subcondition(fulfillment_and_execute.condition)
+
+        # fulfill abort branch
+        fulfillment_and_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+        subfulfillment_user.sign(escrow_tx_fulfillment_message, crypto.SigningKey(user_sk))
+        fulfillment_and_abort.add_subfulfillment(subfulfillment_user)
+        fulfillment_and_abort.add_subfulfillment(fulfillment_timeout, weight=-1)
+        escrow_fulfillment.add_subfulfillment(fulfillment_and_abort)
+
+        escrow_tx_abort['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+
+        # out-of-time validation (abort)
+        with pytest.raises(exceptions.DoubleSpend):
+            b.validate_transaction(escrow_tx_abort)
+        assert b.is_valid_transaction(escrow_tx_abort) is False
+

tests/doc/run_doc_python_server_api_examples.py

@@ -106,6 +106,7 @@ sleep(8)
 
 # retrieve the transaction
 tx_multisig_retrieved = b.get_transaction(tx_multisig_signed['id'])
+assert tx_multisig_retrieved is not None
 
 print(json.dumps(tx_multisig_retrieved, sort_keys=True, indent=4, separators=(',', ':')))
 
@@ -115,7 +116,11 @@ tx_multisig_retrieved_id = b.get_owned_ids(testuser2_pub).pop()
 tx_multisig_transfer = b.create_transaction([testuser1_pub, testuser2_pub], testuser3_pub, tx_multisig_retrieved_id, 'TRANSFER')
 tx_multisig_transfer_signed = b.sign_transaction(tx_multisig_transfer, [testuser1_priv, testuser2_priv])
 
-b.validate_transaction(tx_multisig_transfer_signed)
+try:
+    b.validate_transaction(tx_multisig_transfer_signed)
+except exceptions.InvalidSignature:
+    import ipdb; ipdb.set_trace()
+    b.validate_transaction(tx_multisig_transfer_signed)
 b.write_transaction(tx_multisig_transfer_signed)
 
 # wait a few seconds for the asset to appear on the blockchain
@@ -151,6 +156,8 @@ b.write_transaction(tx_mimo_signed)
 
 print(json.dumps(tx_mimo_signed, sort_keys=True, indent=4, separators=(',', ':')))
 
+sleep(8)
+
 """
 Threshold Conditions
 """
@@ -298,3 +305,183 @@ assert b.is_valid_transaction(hashlock_fulfill_tx) == hashlock_fulfill_tx
 
 b.write_transaction(hashlock_fulfill_tx)
 print(json.dumps(hashlock_fulfill_tx, sort_keys=True, indent=4, separators=(',', ':')))
+
+
+"""
+Timeout Conditions
+"""
+# Create transaction template
+tx_timeout = b.create_transaction(b.me, None, None, 'CREATE')
+
+# Set expiry time (12 secs from now)
+time_sleep = 12
+time_expire = str(float(util.timestamp()) + time_sleep)
+
+# only valid if the server time <= time_expire
+condition_timeout = cc.TimeoutFulfillment(expire_time=time_expire)
+
+# The conditions list is empty, so we need to append a new condition
+tx_timeout['transaction']['conditions'].append({
+    'condition': {
+        'details': json.loads(condition_timeout.serialize_json()),
+        'uri': condition_timeout.condition.serialize_uri()
+    },
+    'cid': 0,
+    'new_owners': None
+})
+
+# conditions have been updated, so hash needs updating
+tx_timeout['id'] = util.get_hash_data(tx_timeout)
+
+# sign transaction
+tx_timeout_signed = b.sign_transaction(tx_timeout, b.me_private)
+
+b.write_transaction(tx_timeout_signed)
+print(json.dumps(tx_timeout, sort_keys=True, indent=4, separators=(',', ':')))
+sleep(8)
+
+# Retrieve the transaction id of tx_timeout
+tx_timeout_id = {'txid': tx_timeout['id'], 'cid': 0}
+
+# Create a template to transfer the tx_timeout
+tx_timeout_transfer = b.create_transaction(None, testuser1_pub, tx_timeout_id, 'TRANSFER')
+
+# Parse the threshold cryptocondition
+timeout_fulfillment = cc.Fulfillment.from_json(
+    tx_timeout['transaction']['conditions'][0]['condition']['details'])
+
+tx_timeout_transfer['transaction']['fulfillments'][0]['fulfillment'] = timeout_fulfillment.serialize_uri()
+
+# no need to sign transaction, like with hashlocks
+for i in range(time_sleep - 4):
+    tx_timeout_valid = b.is_valid_transaction(tx_timeout_transfer) == tx_timeout_transfer
+    seconds_to_timeout = int(float(time_expire) - float(util.timestamp()))
+    print('tx_timeout valid: {} ({}s to timeout)'.format(tx_timeout_valid, seconds_to_timeout))
+    sleep(1)
+
+"""
+Escrow Conditions
+"""
+# retrieve the last transaction of testuser2
+tx_retrieved_id = b.get_owned_ids(testuser2_pub).pop()
+
+# Create escrow template with the execute and abort address
+tx_escrow = b.create_transaction(testuser2_pub, [testuser2_pub, testuser1_pub], tx_retrieved_id, 'TRANSFER')
+
+# Set expiry time (12 secs from now)
+time_sleep = 12
+time_expire = str(float(util.timestamp()) + time_sleep)
+
+# Create escrow and timeout condition
+condition_escrow = cc.ThresholdSha256Fulfillment(threshold=1)  # OR Gate
+condition_timeout = cc.TimeoutFulfillment(expire_time=time_expire)  # only valid if now() <= time_expire
+
+# Create execute branch
+condition_execute = cc.ThresholdSha256Fulfillment(threshold=2)  # AND gate
+condition_execute.add_subfulfillment(cc.Ed25519Fulfillment(public_key=testuser1_pub))  # execute address
+condition_execute.add_subfulfillment(condition_timeout)  # federation checks on expiry
+condition_escrow.add_subfulfillment(condition_execute)
+
+# Create abort branch
+condition_abort = cc.ThresholdSha256Fulfillment(threshold=2)  # AND gate
+condition_abort.add_subfulfillment(cc.Ed25519Fulfillment(public_key=testuser2_pub))  # abort address
+condition_abort.add_subfulfillment(condition_timeout, weight=-1)  # the negative weight inverts the condition
+condition_escrow.add_subfulfillment(condition_abort)
+
+# Update the condition in the newly created transaction
+tx_escrow['transaction']['conditions'][0]['condition'] = {
+    'details': json.loads(condition_escrow.serialize_json()),
+    'uri': condition_escrow.condition.serialize_uri()
+}
+
+# conditions have been updated, so hash needs updating
+tx_escrow['id'] = util.get_hash_data(tx_escrow)
+
+# sign transaction
+tx_escrow_signed = b.sign_transaction(tx_escrow, testuser2_priv)
+
+# some checks
+assert b.validate_transaction(tx_escrow_signed) == tx_escrow_signed
+assert b.is_valid_transaction(tx_escrow_signed) == tx_escrow_signed
+
+print(json.dumps(tx_escrow_signed, sort_keys=True, indent=4, separators=(',', ':')))
+b.write_transaction(tx_escrow_signed)
+sleep(8)
+
+# Retrieve the last transaction of thresholduser1_pub
+tx_escrow_id = {'txid': tx_escrow_signed['id'], 'cid': 0}
+
+# Create a base template for output transaction
+tx_escrow_execute = b.create_transaction([testuser2_pub, testuser1_pub], testuser1_pub, tx_escrow_id, 'TRANSFER')
+
+# Parse the threshold cryptocondition
+escrow_fulfillment = cc.Fulfillment.from_json(
+    tx_escrow['transaction']['conditions'][0]['condition']['details'])
+
+subfulfillment_testuser1 = escrow_fulfillment.get_subcondition_from_vk(testuser1_pub)[0]
+subfulfillment_testuser2 = escrow_fulfillment.get_subcondition_from_vk(testuser2_pub)[0]
+subfulfillment_timeout = escrow_fulfillment.subconditions[0]['body'].subconditions[1]['body']
+
+# Get the fulfillment message to sign
+tx_escrow_execute_fulfillment_message = \
+    util.get_fulfillment_message(tx_escrow_execute,
+                                 tx_escrow_execute['transaction']['fulfillments'][0],
+                                 serialized=True)
+
+escrow_fulfillment.subconditions = []
+
+# fulfill execute branch
+fulfillment_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+subfulfillment_testuser1.sign(tx_escrow_execute_fulfillment_message, crypto.SigningKey(testuser1_priv))
+fulfillment_execute.add_subfulfillment(subfulfillment_testuser1)
+fulfillment_execute.add_subfulfillment(subfulfillment_timeout)
+escrow_fulfillment.add_subfulfillment(fulfillment_execute)
+
+# do not fulfill abort branch
+condition_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+condition_abort.add_subfulfillment(subfulfillment_testuser2)
+condition_abort.add_subfulfillment(subfulfillment_timeout, weight=-1)
+escrow_fulfillment.add_subcondition(condition_abort.condition)
+
+# create fulfillment and append to transaction
+tx_escrow_execute['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+
+# Time has expired, hence the abort branch can redeem
+tx_escrow_abort = b.create_transaction([testuser2_pub, testuser1_pub], testuser2_pub, tx_escrow_id, 'TRANSFER')
+
+# Parse the threshold cryptocondition
+escrow_fulfillment = cc.Fulfillment.from_json(
+    tx_escrow['transaction']['conditions'][0]['condition']['details'])
+
+subfulfillment_testuser1 = escrow_fulfillment.get_subcondition_from_vk(testuser1_pub)[0]
+subfulfillment_testuser2 = escrow_fulfillment.get_subcondition_from_vk(testuser2_pub)[0]
+subfulfillment_timeout = escrow_fulfillment.subconditions[0]['body'].subconditions[1]['body']
+
+tx_escrow_abort_fulfillment_message = \
+    util.get_fulfillment_message(tx_escrow_abort,
+                                 tx_escrow_abort['transaction']['fulfillments'][0],
+                                 serialized=True)
+escrow_fulfillment.subconditions = []
+
+# Do not fulfill execute branch
+condition_execute = cc.ThresholdSha256Fulfillment(threshold=2)
+condition_execute.add_subfulfillment(subfulfillment_testuser1)
+condition_execute.add_subfulfillment(subfulfillment_timeout)
+escrow_fulfillment.add_subcondition(condition_execute.condition)
+
+# Fulfill abort branch
+fulfillment_abort = cc.ThresholdSha256Fulfillment(threshold=2)
+subfulfillment_testuser2.sign(tx_escrow_abort_fulfillment_message, crypto.SigningKey(testuser2_priv))
+fulfillment_abort.add_subfulfillment(subfulfillment_testuser2)
+fulfillment_abort.add_subfulfillment(subfulfillment_timeout, weight=-1)
+escrow_fulfillment.add_subfulfillment(fulfillment_abort)
+
+tx_escrow_abort['transaction']['fulfillments'][0]['fulfillment'] = escrow_fulfillment.serialize_uri()
+
+for i in range(time_sleep - 4):
+    valid_execute = b.is_valid_transaction(tx_escrow_execute) == tx_escrow_execute
+    valid_abort = b.is_valid_transaction(tx_escrow_abort) == tx_escrow_abort
+
+    seconds_to_timeout = int(float(time_expire) - float(util.timestamp()))
+    print('tx_execute valid: {} - tx_abort valid {} ({}s to timeout)'.format(valid_execute, valid_abort, seconds_to_timeout))
+    sleep(1)