# Hash

When you're building on Polkadot, you'll often need [hashes](https://docs.polkadot.com/polkadot-protocol/parachain-basics/cryptography/#hash-functions) — to verify files, derive stable identifiers, or work with chain primitives. The `pop hash` command gives you a fast, convenient way to generate these hashes without juggling separate tools.

You can also run the command as `pop h`.

## What you can use it for

* Verify the integrity of artifacts (WASM, configs, datasets) before committing or deploying.
* Turn strings or hex into deterministic IDs for testing or scripting.
* Hash raw transaction/storage bytes when inspecting or debugging.
* Produce quick, non-cryptographic checksums during development loops.

## Quick examples

```bash
# Verify a string or small blob (cryptographic)
pop hash sha2 256 "hello world"

# Hash raw hex bytes (great for tx/storage inspection)
pop hash keccak 256 0x68656c6c6f776f726c64

# Check a runtime you are about to deploy
pop hash blake2 256 /path/to/your/file.wasm

# Append the original bytes to the hash (BLAKE2 or TwoX only)
pop hash blake2 256 --concat "hello world"
```

## Supported algorithms and lengths

| Subcommand | Alias | Lengths (bits)    | `--concat` |
| ---------- | ----- | ----------------- | ---------- |
| `blake2`   | `b2`  | 64, 128, 256, 512 | Yes        |
| `keccak`   | `kk`  | 256, 512          | No         |
| `sha2`     | `s2`  | 256               | No         |
| `twox`     | `xx`  | 64, 128, 256      | Yes        |

## Input handling

The positional `data` argument is inspected in this order:

* If it matches an existing path, Pop reads the file contents. The file must be 3 MiB or smaller.
* If it starts with `0x`, Pop parses it as hex bytes.
* Otherwise, Pop hashes the raw string bytes.

## Output

Pop prints the hash as lowercase hex without a `0x` prefix. If you use `--concat`, the output is the hash bytes followed by the original input bytes, all hex-encoded.

## Errors and constraints

* Unsupported length: `unsupported length: <length>`
* Path exists but is not a file: `specified path is not a file`
* File too large: `file size exceeds maximum code size`

## Tips

* Input can be plain text, 0x-prefixed hex, or a file path — Pop detects it for you.
* Choose the algorithm that fits the job:
  * SHA-2: dependable, broadly used.
  * BLAKE2: fast and secure (widely used in the Polkadot ecosystem).
  * Keccak: common in EVM tooling and ecosystems.
  * xxHash (TwoX): very fast, non-cryptographic for dev workflows.
* Pick an output length that matches your target (256-bit is a solid default; 512-bit for extra margin, 64/128-bit for speedier non-crypto checks).