In the Cosmos SDK, an _account_ designates a pair of _public key_`PubKey` and _private key_`PrivKey`. The `PubKey` can be derived to generate various `Addresses`, which are used to identify users (among other parties) in the application. `Addresses` are also associated with [`message`s](../building-modules/messages-and-queries.md#messages) to identify the sender of the `message`. The `PrivKey` is used to generate [digital signatures](#signatures) to prove that an `Address` associated with the `PrivKey` approved of a given `message`.
For HD key derivation the Cosmos SDK uses a standard called [BIP32](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki). The BIP32 allows users to create an HD wallet (as specified in [BIP44](https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki)) - a set of accounts derived from an initial secret seed. A seed is usually created from a 12- or 24-word mnemonic. A single seed can derive any number of `PrivKey`s using a one-way cryptographic function. Then, a `PubKey` can be derived from the `PrivKey`. Naturally, the mnemonic is the most sensitive information, as private keys can always be re-generated if the mnemonic is preserved.
The principal way of authenticating a user is done using [digital signatures](https://en.wikipedia.org/wiki/Digital_signature). Users sign transactions using their own private key. Signature verification is done with the associated public key. For on-chain signature verification purposes, we store the public key in an `Account` object (alongside other data required for a proper transaction validation).
-`secp256k1`, as implemented in the [Cosmos SDK's `crypto/keys/secp256k1` package](https://github.com/cosmos/cosmos-sdk/blob/v0.42.1/crypto/keys/secp256k1/secp256k1.go).
-`secp256r1`, as implemented in the [Cosmos SDK's `crypto/keys/secp256r1` package](https://github.com/cosmos/cosmos-sdk/blob/master/crypto/keys/secp256r1/pubkey.go),
-`tm-ed25519`, as implemented in the [Cosmos SDK `crypto/keys/ed25519` package](https://github.com/cosmos/cosmos-sdk/blob/v0.42.1/crypto/keys/ed25519/ed25519.go). This scheme is supported only for the consensus validation.
`Addresses` and `PubKey`s are both public information that identifies actors in the application. `Account` is used to store authentication information. The basic account implementation is provided by a `BaseAccount` object.
Each account is identified using `Address` which is a sequence of bytes derived from a public key. In the Cosmos SDK, we define 3 types of addresses that specify a context where an account is used:
Address construction algorithm is defined in [ADR-28](https://github.com/cosmos/cosmos-sdk/blob/master/docs/architecture/adr-028-public-key-addresses.md).
Here is the standard way to obtain an account address from a `pub` public key:
Of note, the `Marshal()` and `Bytes()` method both return the same raw `[]byte` form of the address. `Marshal()` is required for Protobuf compatibility.
For user interaction, addresses are formatted using [Bech32](https://en.bitcoin.it/wiki/Bech32) and implemented by the `String` method. The Bech32 method is the only supported format to use when interacting with a blockchain. The Bech32 human-readable part (Bech32 prefix) is used to denote an address type. Example:
Public keys in Cosmos SDK are defined by `cryptotypes.PubKey` interface. Since public keys are saved in a store, `cryptotypes.PubKey` extends the `proto.Message` interface:
Public Keys are not used to reference accounts (or users) and in general are not used when composing transaction messages (with few exceptions: `MsgCreateValidator`, `Validator` and `Multisig` messages).
For user interactions, `PubKey` is formatted using Protobufs JSON ([ProtoMarshalJSON](https://github.com/cosmos/cosmos-sdk/blob/release/v0.42.x/codec/json.go#L12) function). Example:
-`Sign(uid string, payload []byte) ([]byte, sdkcrypto.PubKey, error)` strictly deals with the signature of the `payload` bytes. You must prepare and encode the transaction into a canonical `[]byte` form. Because protobuf is not deterministic, it has been decided in [ADR-020](../architecture/adr-020-protobuf-transaction-encoding.md) that the canonical `payload` to sign is the `SignDoc` struct, deterministically encoded using [ADR-027](../architecture/adr-027-deterministic-protobuf-serialization.md). Note that signature verification is not implemented in the Cosmos SDK by default, it is deferred to the [`anteHandler`](../core/baseapp.md#antehandler).
-`NewAccount(uid, mnemonic, bip39Passwd, hdPath string, algo SignatureAlgo) (Info, error)` creates a new account based on the [`bip44 path`](https://github.com/bitcoin/bips/blob/master/bip-0044.mediawiki) and persists it on disk. The `PrivKey` is **never stored unencrypted**, instead it is [encrypted with a passphrase](https://github.com/cosmos/cosmos-sdk/blob/v0.40.0-rc3/crypto/armor.go) before being persisted. In the context of this method, the key type and sequence number refer to the segment of the BIP44 derivation path (for example, `0`, `1`, `2`, ...) that is used to derive a private and a public key from the mnemonic. Using the same mnemonic and derivation path, the same `PrivKey`, `PubKey` and `Address` is generated. The following keys are supported by the keyring:
-`ExportPrivKeyArmor(uid, encryptPassphrase string) (armor string, err error)` exports a private key in ASCII-armored encrypted format using the given passphrase. You can then either import the private key again into the keyring using the `ImportPrivKey(uid, armor, passphrase string)` function or decrypt it into a raw private key using the `UnarmorDecryptPrivKey(armorStr string, passphrase string)` function.
