> ## Documentation Index
> Fetch the complete documentation index at: https://cosmos-docs-cosmjs-docs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Signing & Key Types

> How EVM signing, public key types, and algo identifiers work in CosmJS.

## How Signing Works

EVM wallets hash the serialized sign document with Keccak-256 before signing,
whereas standard wallets use SHA-256:

```text theme={"system"}
signBytes = SignDoc.encode(signDoc)

# Standard
hashedMessage = sha256(signBytes)

# EVM
hashedMessage = keccak256(signBytes)

signature = secp256k1_sign(hashedMessage, privateKey)
```

The actual elliptic curve operation and signature format (64 bytes: `r || s`) are
identical — only the pre-signing hash function differs.

## Public Key Types

CosmJS represents public keys in two forms: Amino JSON and Protobuf. EVM chains
use distinct types in each format to signal that the key requires Keccak-based
address derivation.

**Amino JSON:**

```typescript theme={"system"}
// Standard
{ type: "tendermint/PubKeySecp256k1", value: "<base64>" }

// EVM
{ type: "os/PubKeyEthSecp256k1", value: "<base64>" }
```

**Protobuf (`Any`):**

```typescript theme={"system"}
// Standard
{ typeUrl: "/cosmos.crypto.secp256k1.PubKey", value: <bytes> }

// EVM
{ typeUrl: "/cosmos.evm.crypto.v1.ethsecp256k1.PubKey", value: <bytes> }
```

The underlying key bytes are identical (33-byte compressed secp256k1). The
different type identifiers tell the chain how to derive the address from the key.

## The Algo Identifier

The `AccountData.algo` field distinguishes EVM accounts from standard ones.
Two naming conventions exist in the ecosystem:

* `"eth_secp256k1"` — used by Keplr wallet, CosmJS wallets, and some chains
* `"ethsecp256k1"` — used by Evmos, Cronos, and other EVM-compatible chains

CosmJS handles both through the `isEthereumSecp256k1Account()` utility:

```typescript theme={"system"}
import { isEthereumSecp256k1Account } from "@cosmjs/amino";

const [account] = await wallet.getAccounts();
if (isEthereumSecp256k1Account(account)) {
  // EVM-compatible account
}
```

The `getAminoPubkey()` function uses this check to select the correct encoding
automatically. This is what `SigningStargateClient` calls internally when
building transactions:

```typescript theme={"system"}
import { getAminoPubkey } from "@cosmjs/amino";

const pubkey = getAminoPubkey(account);
// Returns EthSecp256k1Pubkey or Secp256k1Pubkey based on account.algo
```