BSIP: 0040 Title: Custom active permissions Authors: Alex Megalokonomos Fabian Schuh Stefan Schießl Status: Draft Type: Protocol Created: 2018-07-25 Discussion: https://github.com/bitshares/bitshares-core/issues/1061 Worker: # Abstract Strengthening user security is one of the main factors to elevate BitShares. In light of recent hacking and phishing attempts this becomes even more important. The need for a more sophisticated account security preceeded the idea for a finer-grained control of account permissions. We propose to add an additional authority to the account, called Custom Active (Permission). The permission contains a list of operationid-to-authority mappings that each grant access to the respective operation as if it were the active permission of the account. Additionally, the arguments of said operation can be restricted. # Motivation Any successfull hacking or phishing attempt on any of the web wallets that are powered by the BitShares Blockchain is bad publicity. The user needs to be educated in account security, and this BSIP aims to ensure all technical possibilities are met while being flexible to allow many use-cases. With this BSIP any user can create keys with specific purpose (everything else is prohibited). We list some possibilities below: - Witness Key: Only allows update signing key and publish price feed - Trading Key: Only allows limit orders (arguments restricted to desired markets), update margin position and transfers (arguments restricted to certain accounts) - Proposal Update Key: Approve proposals (2FA comes to mind) - Faucet Key: Allow only to create accounts - Withdrawal Key: Allow another account to transfer funds to himself - Cold Storage Key: Only allow to move funds to the Hot Wallet The above list of named keys is nothing that is known to the backend as the backend should have an abstract implementation. The UI could provide a button "Create Trading Key" that properly configures the respective custom active permission entry. # Rational Custom active permission is a list of `custom active authorities`. A `custom active authority` contains an `operation_id`, an `authority` (just like with active permission) and `asserts` than can be used to restrict arguments and is only valid a certain time period (`valid_from` and `valid_to`). When handling incoming signed transactions, the backend checks for each operation if there is a `custom active authority` for any of the required accounts. If all operations within the transaction have a matching `custom active authority` (match means same `operationid`, now is within `valid_to` and `valid_from` and all `asserts` pass), then active authority of the corresponding account is granted. # Specification All descriptions in this section are on a pseudo/prosa level and no recommendation how it can best be implemented or serialized. They are meant to facilitate the understanding. ### Custom active permission and custom active authority A `custom_active_permission` looks like follows (in JSON/pseudo for clarification): ``` custom_active_permission = list of custom_active_authority items custom_active_authority = { valid_from, // timestamp when this is active, defaults to now valid_to, // timestamp when this is invalid, defaults to 1 month operationid, // operationid of the target operation, authority, // same as for the existing authortities (multisig with weighted accounts or keys), asserts // see below } ``` Note: This assumes `custom_active_permission` is stored within `account_object`. Actual implementation details left to the implementer, as long as every `custom_active_permission` can be assigned to exactly one account. ### Asserts The `asserts` is a list of `assert_objects` that are all together evaluated with `and` logic to evaluate a match ``` asserts = list of assert_objects assert_object = { argument, // target argument of the operationid function, // functionid to do the assert data, // stores data specific to the chosen function state // if this assert is statefull } ``` List of possible asserts are: | function | data | state | | ------------- |:-------------:| -----:| | `any` | [`list`, `of`, `allowed`, `values`] | stateless | | `none` | [`none`, `of`, `these`, `values`] | stateless | | `lt, le, gt, ge` | `comparative` | stateless | | `length` | [`min`, `max`] | stateless | | `limit` | [`max_cumsum`, `interval_in_sec`] | [`current_cumsum`, `interval_began`] | | `limit_monthly` | [`max_cumsum`, `interval_in_months`] | [`current_cumsum`, `interval_began`] | | `contains` | [`list`, `of`, `allowed`, `fields`] | stateless | All asserts apply to `int`, `string` and `object_ids`. There is no type converstion, incompatible type means assert failure. Any more sophisticated data types are not included yet. In the following we list possible `asserts`. Mentioning `argument value` refers to the value of the argument of the operation specified `argument` in `assert_object`. #### `any` Stateless assert, all argument types. `Argument value` must be equal to one of values in the data list #### `none` Stateless assert, all argument types. `Argument value` must NOT be equal to any of the values in the list. #### `lt, le, gt, ge` Stateless assert, only `int` type arguments. - `lt`: `Argument value` must be less than `comparitive` - `lt`: `Argument value` must be less than or equal to `comparitive` - `lt`: `Argument value` must be greater than `comparitive` - `lt`: `Argument value` must be greater than or equal to `comparitive` #### `length` Stateless assert, only `string` type arguments. Length of string (or encrypted string in case of memo) must be within `min` and `max`, inclusive. One of the bounds can be empty to indicate unlimited. #### `limit` Statefull assert, only `int` type arguments. When the authority is created, `interval_began` is set to `valid_from` from its custom active authority and `max_cumsum` to `0`. Incoming operations are first tried to match all stateless asserts, and if all passes continue with statefull asserts. If `now > interval_began + interval_in_sec`, then set `max_cumsum = 0` and set `interval_began = now`. The assert that needs to pass is now `current_cumsum + incoming value <= max_cumsum`. If all asserts are passed, update `current_cumsum = current_cumsum + incoming value` of all involved statefull asserts. #### `limit_monthly` Statefull assert, only `int` type arguments. Analogue to `limit`, but `interval_began` is initially set to `month(valid_from)` and set to `month(now)` on update, additionally the time assert is `month(now) >= interval_began + interval_in_months` (include logic for month overflow when year changes). #### `contains_only` Stateless assert, only for dictionary type objects like `options`. The `argument` of the operation is a dictionary type objects and is only allowed to contain the attributes in the data list. ### Simple Example Assume account A and B and some unrelated key K. Furthermore A has a custom active authority in the following way: ``` custom active authority = { valid_from: 7.7.2018 00:00 valid_to: 8.7.2018 00:00 operationid: transfer, authority: { threshold: 1 key_auth: [K, 1] account_auth: [] }, asserts: [ { argument: to function: any, data: [B] } ] } ``` That has the consquence now that a transfer transaction sending funds away from A can be signed with key K as long as the receiver is B. Note: This is just an illustration of a possible serialization, not a specification of the serialized format. ### Outline of handling incoming transactions When a signed transaction arrives and before the backend evaluates if all necessary authorities are present through the signatures, do the following: - iterate over required accounts and for each account, iterate over all operations within the transactions that require the active authority of this account - iterate the `custom_active_authorities` of said account - if a `custom_active_authority` is found that matches (same `operationid` and passes all `asserts`), remember that and stop iterating the authorities and continue until all operations are checked - if the account has a `custom active authority` match for every operation in the transaction that requires it, then grant the `active authority` of said account. If no match is found, treat as if no authority was given Note: - A `custom_active_authority` can only grant the `active authority` of the corresponding account, nothing more ### Modification to the backend * Extend the account object to store custom active permission that includes a list of custom active authorities. Multiple custom active authority entries are possible for one operation * If the active authority of the account is updated, all custom active authorities need to be confirmed in the update. Every unconfirmed one is deleted otherwise * Extend `account_update` or create a new operation to allow changing the custom active permission * Operation-specific authorities (if present) must be evaluated in incoming transactions * Additional committee parameters may be needed to limit the extend of usage of this feature Notes: The implementation must not differentiate on which operation the custom active authority is applied, all operations are treated in same fashion # Milestones We propose do split the implmentation into two milestones: 1. Implementation of basic functionaliy to allow custom active permissions and authorities, including `range`, `length` and `any` `asserts` 2. Evaluation of stateful asserts (performance) and if positive, implementation of `limit` and `limit_monthly` `asserts` This approach allows as well to add other asserts at a later stage (with a new BSIP). # Discussion To be found in the [issue](https://github.com/bitshares/bitshares-core/issues/1061) and [pull request](https://github.com/bitshares/bsips/pull/86). # Summary for Shareholders Bad publicity in terms of security can have very negative effect on the BTS value. This BSIP allows that traders can e.g. use a trading key, witnesses can use their witness key and a faucet can use a faucet key. If then for some reason the key or witness/faucet server becomes compromised, such a key can do little harm to the account holders, minimizing the risk. This BSIP opens up a lot of use-cases as presented in Motivation section. The intention is to not alter any existing logic of the permission system, which reduces the risk of malfunctioning. # Copyright This document is placed in the public domain.