# `Cartouche.Transaction.Signature`
[🔗](https://github.com/zenhive/cartouche/blob/main/lib/cartouche/transaction/signature.ex#L1)

Shared signature-field helpers for typed-transaction structs that carry the
`signature_y_parity` / `signature_r` / `signature_s` triple
(EIP-1559 `V2`, EIP-4844 `V3`, and any future post-EIP-2718 type).

These functions operate on the struct as a plain map, so they work uniformly
across the typed-transaction modules without coupling them to one another.

# `add`

```elixir
@spec add(map(), boolean(), <<_::256>>, <<_::256>>) :: map()
```

Attaches explicit signature fields (`y_parity`, `r`, `s`) to a transaction
struct. `r` and `s` must be exactly 32 bytes and `v` a boolean y-parity.

# `add_packed`

```elixir
@spec add_packed(map(), <<_::512, _::_*8>>) :: map()
```

Attaches a packed `r <> s <> v` signature to a transaction struct.

# `get`

```elixir
@spec get(map()) :: {:ok, binary()} | {:error, String.t()}
```

Recovers the packed `r <> s <> y_parity` signature from a signed transaction,
or `{:error, "transaction missing signature"}` when any signature field is nil.

# `y_parity_from_v`

```elixir
@spec y_parity_from_v(binary()) :: boolean()
```

Derives EIP-155-style y-parity from a packed recovery `v` byte sequence.

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*Consult [api-reference.md](api-reference.md) for complete listing*