# Auth :::{Important} Terra's auth module inherits from Cosmos SDK's [`auth`](https://docs.cosmos.network/master/modules/auth/) module. This document is a stub and covers mainly important Terra-specific notes about how it is used. ::: Terra's Auth module extends the functionality from Cosmos SDK's `auth` module with a modified ante handler, which applies basic transaction validity checks, such as signatures, nonces, and auxiliary fields. This module also defines a special vesting account type that handles the logic for token vesting from the Luna presale. ## Gas Fee Like all transactions on the Terra blockchain, [`MsgSend`](spec-bank.md#msgsend) and [`MsgMultiSend`](spec-bank.md#msgmultisend) incur gas fees. These fees are determined by a validator's minimum gas price and the complexity of the transaction. More complex transactions incur higher fees. Gas fees are specified by the sender when a transaction is outbound. For more information on how gas is calculated, see [fees](../how-to/terrad/using-terrad.md#fees). ## Parameters The subspace for the Auth module is `auth`. ```go type Params struct { MaxMemoCharacters uint64 `json:"max_memo_characters" yaml:"max_memo_characters"` TxSigLimit uint64 `json:"tx_sig_limit" yaml:"tx_sig_limit"` TxSizeCostPerByte uint64 `json:"tx_size_cost_per_byte" yaml:"tx_size_cost_per_byte"` SigVerifyCostED25519 uint64 `json:"sig_verify_cost_ed25519" yaml:"sig_verify_cost_ed25519"` SigVerifyCostSecp256k1 uint64 `json:"sig_verify_cost_secp256k1" yaml:"sig_verify_cost_secp256k1"` } ``` ### MaxMemoCharacters The maximum permitted number of characters in the memo of a transaction. - type: `uint64` - default: `256` ### TxSigLimit The maximum number of signers in a transaction. A single transaction can have multiple messages and multiple signers. Because the sig verification cost is generally higher than other operations, the number of signers is limited to 100. - type: `uint64` - default: `100` ### TxSizeCostPerByte The cost per byte used to compute the gas consumption of a transaction. `TxSizeCostPerByte * txsize`. - type: `uint64` - default: `10` ### SigVerifyCostED25519 The gas cost for verifying ED25519 signatures. - type: `uint64` - default: `590` ### SigVerifyCostSecp256k1 The gas cost for verifying Secp256k1 signatures. - type: `uint64` - default: `1000`