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# Algorand Specifications

The following opcodes allow for _inner transactions_.

Inner transactions allow Applications to have many of the effects of a true top-level transaction, programmatically. However, they are different in significant ways. The most important differences are that:

- They are not signed;

- Duplicates are not rejected;

- They do not appear in the block in the usual way.

Instead, their effects are noted in metadata associated with their top-level application call transaction.

An inner transaction’s _sender_ **MUST** be the [SHA512/256 hash](https://specs.algorand.co/crypto/crypto-sha512-256) of the Application ID (prefixed by `appID`), or an account that has been rekeyed to that hash.

In Version 5, inner transactions may perform `pay`, `axfer`, `acfg`, and `afrz` effects.

After executing an inner transaction with `itxn_submit`, the effects of the transaction are visible beginning with the next instruction with, for example, `balance` and `min_balance` checks.

In Version 6, inner transactions may also perform `keyreg` and `appl` effects. Inner `appl` calls fail if they attempt to invoke a program with a Version less than Version 4, or if they attempt to opt-in to an app with a Clear State Program less than Version 4.

In Version 5, only a subset of the transaction’s header fields may be set: `Type` / `TypeEnum`, `Sender`, and `Fee`.

In Version 6, header fields `Note` and `RekeyTo` may also be set.

For the specific (non-header) fields of each transaction type, any field may be set. This allows, for example, clawback transactions, asset opt-ins, and asset creates in addition to the more common uses of `axfer` and `acfg`.

All fields default to the zero value, except those described under `itxn_begin`.

Fields may be set multiple times, but may not be read. The most recent setting is used when `itxn_submit` executes. For this purpose `Type` and `TypeEnum` are considered to be the same field. When using `itxn_field` to set an array field (`ApplicationArgs`, `Accounts`, `Assets`, or `Applications`) each use adds an element to the end of the array, rather than setting the entire array at once.

`itxn_field` fails immediately for unsupported fields, unsupported transaction types, or improperly typed values for a particular field. `itxn_field` makes acceptance decisions entirely from the field and value provided, never considering previously set fields.

Illegal interactions between fields, such as setting fields that belong to two different transaction types, are rejected by `itxn_submit`.

| OPCODE         | DESCRIPTION                                                                 |
|----------------|-----------------------------------------------------------------------------|
| `itxn_begin`   | begin preparation of a new inner transaction in a new transaction group     |
| `itxn_next`    | begin preparation of a new inner transaction in the same transaction group  |
| `itxn_field f` | set field F of the current inner transaction to A                           |
| `itxn_submit`  | execute the current inner transaction group. Fail if executing this group would exceed the inner transaction limit, or if any transaction in the group fails. |
| `itxn f`       | field F of the last inner transaction                                       |
| `itxna f i`    | Ith value of the array field F of the last inner transaction                |
| `itxnas f`     | Ath value of the array field F of the last inner transaction                |
| `gitxn t f`    | field F of the Tth transaction in the last inner group submitted            |
| `gitxna t f i` | Ith value of the array field F from the Tth transaction in the last inner group submitted |
| `gitxnas t f`  | Ath value of the array field F from the Tth transaction in the last inner group submitted |