1. Overview

An account identifies a participant in an EOSIO blockchain. A participant can be an individual or a group depending on the assigned permissions within the account. Accounts also represent the smart contract actors that push and receive actions to and from other accounts in the blockchain. Actions are always contained within transactions. A transaction can be one or more atomic actions.

Permissions associated with an account are used to authorize actions and transactions to other accounts. Each permission is linked to an authority table which contains a threshold that must be reached in order to allow the action associated with the given permission to be authorized for execution. The following diagram illustrates the relationship between accounts, permissions, and authorities.

The example above depicts alice's account, her named permissions along with their hierarchical dependencies, and her linked active authority table. It also shows that a weight threshold of two must be reached in alice's active authority in order to allow an action associated with the active permission to be executed by or on behalf of alice.

2. Accounts

Each account is identified by a human readable name between 1 and 12 characters in length. The characters can include a-z, 1-5, and optional dots (.) except the last character. This allows exactly one exa ($2^{60}$) accounts minus one:

$31^{1} \cdot \sum_{n=0}^{n=11} 32^{n} = 2^{60}-1 = 1,152,921,504,606,846,975$

which is in the order of $1 \times 10^{18}$.

Ownership of each account on an EOSIO blockchain is solely determined by the account name. Therefore, an account can update its keys without having to redistribute them to other parties.

2.1. Account Schema

Besides the account name, the blockchain associates other fields with each account instance stored in the chain database, such as ram quota/usage, cpu/net limits/weights, voter info, etc. (see account schema below). More importantly, each account holds the list of named permissions assigned to it. This allows a flexible permission structure that makes single or multi-user authorizations possible (see 3. Permissions).

account schema

Name	Type	Description
account_name	name	encoded 13-char account name
head_block_num	uint32_t	last block account was referenced
head_block_time	time_point	last time account was referenced
privileged	bool	True, if privileged account, False otherwise
last_code_update	time_point	time account code was set/updated
created	time_point	time account was created
core_liquid_balance	asset	current balance of token asset
ram_quota	int64_t	maximum RAM amount for account
net_weight	int64_t	weight for net limit percentage (weight/total)
cpu_weight	int64_t	weight for cpu limit percentage (weight/total)
net_limit	account_resource_limit	total net used, available, and max
cpu_limit	account_resource_limit	total cpu used, available, and max
ram_usage	int64_t	amount of RAM in bytes used by account
permissions	array of permission	list of named permissions
total_resources	variant	total cpu/net weights for all accounts
self_delegated_bandwidth	variant	cpu/net stake delegated from self
refund_request	variant	cpu/net refund amounts for token unstaking
voter_info	variant	name of voter, proxy or producers, vote stake
rex_info	variant	vote stake and rex balance if applicable

The name type consists of a 64-bit value that encodes alphanumeric characters into 5-bit chunks, except the last character, if any, which uses a 4-bit chunk. The name type is used to encode account names, action names, etc. The time_point type stores timestamps in microseconds. The asset type associates a currency or token symbol with a given amount. The account_resource_limit type keeps track of the amount used, available, and maximum that can be used in a given window for the given resource (NET or CPU). The permission type holds the list of permission levels associated with the account (see 3. Permissions).

2.2. Actions and Transactions

Besides identifying participants in an EOSIO blockchain, actions and transactions are the other reason for accounts to exist. An action requires one or more actors to push or send the action, and a receiver account to whom the action is directed. A receiver account is also needed when leaving proof, in an action receipt, that the action was pushed to the intended recipient.

In contrast, transactions are agnostic to accounts, although there is an indirect link to them through their associated keys. Transactions are signed using one or more signing keys belonging to the one or more actors involved in the actions that form the transaction. This can be the receiving account itself or other authorized actors specified on the authority table from the receiving account's permission.

3. Permissions

Permissions control what EOSIO accounts can do and how actions are authorized. This is accomplished through a flexible permission structure that links each account to a list of hierarchical named permissions, and each named permission to an authority table (see permission schema below).

permission schema

Name	Type	Description
perm_name	name	named permission
parent	name	parent's named permission
required_auth	authority	associated authority table

The parent field links the named permission level to its parent permission. This is what allows hierarchical permission levels in EOSIO.

3.1. Permission Levels

A named permission may be created under another permission, thereby allowing a hierarchical parent-children permission structure. This makes implicit action authorizations possible by allowing a given actor:child-permission authorization within an action to be implicitly satisfied if the actor:parent-permission is also satisfied. An authorization quorum or "threshold" must still be met for the action to be authorized for execution (see 3.2.2. Authority Threshold).

Every account has two default named permissions when created, owner and active. They have a parent-child relationship by default, although this can be customized by adding other permission levels and hierarchies.

3.1.1. Owner permission

The owner permission sits at the root of the permission hierarchy for every account. It is therefore the highest relative permission an account can have within its permission structure. Although the owner permission can do anything a lower level permission can, it is typically used for recovery purposes when a lower permission has been compromised. As such, keys associated with the owner permission are typically kept in cold storage, not used for signing regular operations.

3.1.2. Active permission

In the current EOSIO implementation, the implicit default permission linked to all actions is active, which sits one level below the owner permission within the hierarchy structure. As a result, the active permission can do anything the owner permission can, except changing the keys associated with the owner. The active permission is typically used for voting, transferring funds, and other account operations. For more specific actions, custom permissions are typically created below the active permission and mapped to specific contracts or actions. Refer to the Creating and Linking Custom Permissions for more details.

3.2. Authority Table

Each account's permission can be linked to an authority table used to determine whether a given action authorization can be satisfied. The authority table contains the applicable permission name and threshold, the "factors" and their weights, all of which are used in the evaluation to determine whether the authorization can be satisfied. The permission threshold is the target numerical value that must be reached to satisfy the action authorization (see authority schema below).

authority schema

Name	Type	Description
threshold	uint32_t	threshold value to satisfy authorization
keys	array of key_weight	list of public keys and weights
accounts	array of permission_level_weight	list of account@permission levels and weights
waits	array of wait_weight	list of time waits and weights

The key_weight type contains the actor's public key and associated weight. The permission_level_weight type consists of the actor's account@permission level and associated weight. The wait_weight contains the time wait and associated weight (used to satisfy action authorizations in delayed user transactions (see Transactions Protocol: 3.6.3. Delayed User Transactions). All of these types allow to define lists of authority factors that are used for satisfaction of action authorizations (see 3.2.1. Authority factors below).

3.2.1. Authority Factors

Every authority table linked to a given permission lists potential "factors" explicitly used in the evaluation of the action authorization. A factor type can be one of the following:

• Actor's account name and permission level
• Actor's public key
• Time wait

The potential actors who may execute the action are specified by either public key or account name in the authority table. Time waits are special factors which are satisfied by publishing a transaction with a delay in excess of the defined time. These carry weights as well that may contribute to satisfy the threshold.

3.2.2. Authority Threshold

Authorization over a given action is determined by satisfying all explicit authorizations specified in the action instance (see Transactions Protocol: 3.4.3. Action Instance). Those are in turn individually satisfied by evaluating each "factor" (account, public key, wait) for satisfaction (potentially recursively) and summing the weights of those that are satisfied. If the sum equals or exceeds the weight threshold, the action is authorized.

3.2.3. Authority Example

The authority table for alice's publish named permission is shown below. According to its contents, in order to authorize an action under that permission, a threshold of two must be reached. Since both bob@active and stacy@active factors have a weight of two, either one can satisfy the action authorization. This means that either bob or stacy with a permission level of active or higher can independently execute any action under alice's publish permission.

Permission	Account / Public Key	Weight	Threshold
publish	bob@active	2	2
	stacy@active	2
	EOS7Hnv4iBfcw2...	1
	EOS3Wo1p9er7fh...	1

Alternatively, it would require two acounts with public keys EOS7Hnv4iBfcw2... and EOS3Wo1p9er7fh... to satisfy the action authorization. This is because each public key has a weight of 1 in the authority table.

3.3. Permission Mapping

Any given account can define a mapping between any of its named permissions and a smart contract or action within that contract. This sets the "minimum permission" required for that contract[::action]. It does not afford, however, any other account any access or authority to execute that contract[::action]. This is by design and the process is controlled by a permission evaluation mechanism, described next.

3.4. Permission Evaluation

When determining whether an action is authorized to be executed, the EOSIO software first checks whether the signatures provided in the transaction are valid (see 3.4.2. Signature Validation). Then it proceeds to check the authorization of all the actions included in the transaction. This is where permissions are evaluated. If there is at least one action that fails to be authorized (by not meeting the authority threshold (see 3.2.2. Authority Threshold), the transaction fails.

3.4.1. Custom Permissions

By default every account on the EOSIO blockchain is linked to the active permission. Again, this can be customized by creating children permissions under active or by creating alternate permissions under owner (see 3.1. Permission Levels). Creating custom permissions under owner (separate from active) is recommended. This is because if the keys associated with the active permission are compromised, the security of the account will not be compromised.

3.4.2. Signature Validation

Satisfying authorities linked to permissions involves first and foremost the validation/recovery of the public keys that signed the transaction. After a signed transaction is received by a node, the set of signatures is extracted from the transaction instance. The set of public keys are then recovered from the signatures. Then for all actions included in the transaction, the node checks that each actor:permission meets or exceeds the minimum permission as defined by the per-account permission links.

Once validated, the set of recovered keys are provided to the authorization manager instance along with the amount of time "waited". The authorization manager then proceeds to check whether the provided "factors" satisfy the authorities, potentially recursing into other linked permission levels/authorities (see 3.2. Authority Table and Transactions Protocol: 3.4. Verify Transaction for more information).