An encrypted date field: Encryptor.Ecto.Binary over the value's ISO 8601 form (ADR-0001 decision 1).

defmodule Payments.Encrypted.Date do
  use Encryptor.Ecto.Date, vault: Payments.Vault
end

defmodule Payments.Cards.Card do
  use Ecto.Schema

  schema "cards" do
    field :merchant_id, :string
    field :date_of_birth, Payments.Encrypted.Date
  end
end

Everything below the cast/parse pair is Encryptor.Ecto.Binary, called rather than copied: the same closed option set, the same declared "table"/"column" context, the same tenant resolution, the same :binary column, the same exception family, and the vault's bytes stored verbatim. Read that module for all of it; only the differences are documented here.

The cast/parse pair

cast/2 is Ecto.Type.cast(:date, value) - Ecto's own caster, so a Date.t/0, an ISO 8601 string, and the %{"year" => _, "month" => _, "day" => _} map a form sends all cast exactly as they would on a plain :date column. The plaintext is Date.to_iso8601/1 and a load parses it with Date.from_iso8601/1, accepting a calendar date and nothing else.

The textual form is not a choice taken here. Cloak.Ecto.Date writes the same bytes: cloak_ecto 1.3.0 serializes every scalar with to_string/1, which for a Date is byte-identical to Date.to_iso8601/1 on the ISO calendar. ADR-0004's migration hands the migrator a legacy plaintext and re-encrypts it verbatim below the schema layer (ADR-0002 decision 3), so a column arriving from Cloak.Ecto.Date is readable through this type because the two agree about what the bytes say. The two datetime types are the exception - see Encryptor.Ecto.NaiveDateTime - and every kind's exact bytes are pinned in test/encryptor/ecto/scalar_types_test.exs.

A payload that decrypts and then does not parse raises Encryptor.Ecto.SerializationError with {:unparsable, :date}: the decrypt succeeded, so it is neither an encryption failure nor an integrity event, which is the row ADR-0001 decision 6 gives that exception. A value that reaches dump/3 without passing cast/2 - through insert_all/3, say - raises ArgumentError naming the shape it was given and never the value.

Everything else

nil is NULL and is not encrypted (decision 7). The column is :binary, not :date - type/1 returns :binary whatever the plaintext was (decision 2), so the database applies no date validation of its own and the migration writes :binary here as it does for Binary. Encrypted columns are not queryable, sortable or uniquely indexable (decision 10), and a date is where that costs the most: where: c.date_of_birth < ^cutoff does not mean what it would on a plain column, and an age filter is a host-side pass over decrypted rows or a redesign, not an index.