Meta-transactions and Generalized Accounts
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In the æternity blockchain, Generalized Accounts provide increased flexibility in transaction authentication. This powerful feature enables custom authorization schemes through the combination of attach transactions and meta-transactions, allowing accounts to implement sophisticated control mechanisms beyond traditional cryptographic signatures.
The journey to creating a generalized account begins with an attach transaction. This special transaction type transforms a standard account into a generalized account by associating it with a smart contract that controls all future authorizations. The attach transaction must include the smart contract code and be signed using the account's standard EdDSA signature. This is a one-way transformation - once an account becomes a generalized account, it cannot revert to a standard account.
The smart contract attached to the account must implement an authentication function that accepts data as input and returns a boolean value indicating whether authentication is successful. This function defines the rules for authorizing transactions from the account, enabling flexible authentication schemes like multi-signature requirements, spending limits, or alternative cryptographic methods.
After an account becomes generalized, all its transactions must be wrapped in meta-transactions. A meta-transaction packages a standard transaction (with its nonce set to zero) along with the necessary authentication data required by the account's smart contract. The meta-transaction includes additional information such as fees and gas needed to execute the smart contract's authorization function.
When the network processes a meta-transaction, it first executes the authentication function in the associated smart contract using the provided authentication data. Only if authentication succeeds does the network process the inner transaction. This two-step process ensures that all transactions follow the custom authorization rules defined in the account's contract while maintaining the security of the network.
A practical example of generalized accounts is enabling æternity transactions to be signed using Bitcoin private keys. The attached smart contract is initialized with the desired public key and implements ECDSA signature verification using the Secp256k1 curve. The authentication function verifies signatures created by the corresponding Bitcoin private key, allowing users to manage their æternity accounts using familiar Bitcoin key management tools.
In this implementation, the contract tracks its own nonce to prevent transaction replay attacks. Users must maintain awareness of the contract's nonce state to ensure proper transaction sequencing. The contract verifies signatures against a Blake2b hash of the transaction data and nonce, providing secure transaction authorization using Bitcoin keypairs.
The implementation of generalized accounts includes careful consideration of potential security risks. To prevent abuse, the system only charges gas for successful authentication attempts, protecting account holders from potential drain attacks through failed authentications. However, this creates a potential risk of resource exhaustion attacks against miners who must execute authentication functions.
To mitigate these risks, authentication functions are restricted from performing expensive chain operations. Miners can also implement rules to reject transactions that appear to be attempting resource exhaustion. These protections ensure the security of both individual accounts and the network as a whole.
Generalized accounts enable numerous sophisticated account management schemes. Beyond alternative signature algorithms, they can implement multi-signature wallets, spending limits based on time periods, and restrictions on transaction types. The flexibility of smart contract-based authorization allows for innovative account control mechanisms while maintaining strong security guarantees.
When implementing generalized accounts, developers must carefully design their authorization functions to include proper integrity checking and replay protection. The power and flexibility of this system require thoughtful implementation to prevent potential security vulnerabilities while enabling advanced account management features.
Generalized Accounts Documentation