diff --git a/lib/ex_ucan/core/keymaterial.ex b/lib/ex_ucan/core/keymaterial.ex
new file mode 100644
index 0000000..4c3f591
--- /dev/null
+++ b/lib/ex_ucan/core/keymaterial.ex
@@ -0,0 +1,10 @@
+# TODO: docs??
+
+defprotocol ExUcan.Core.Keymaterial do
+  alias ExUcan.Core.Structs.UcanPayload
+  @spec did(struct()) :: String.t()
+  def did(type)
+
+  @spec sign(struct(), UcanPayload.t()) :: binary()
+  def sign(type, payload)
+end
diff --git a/lib/ex_ucan/core/plugins.ex b/lib/ex_ucan/core/plugins.ex
new file mode 100644
index 0000000..108da09
--- /dev/null
+++ b/lib/ex_ucan/core/plugins.ex
@@ -0,0 +1,20 @@
+defmodule ExUcan.Core.Plugins do
+  # TODO: docs
+
+  @spec verify_issuer_alg(String.t(), String.t()) :: boolean()
+  def verify_issuer_alg(did, jwt_alg) do
+
+  end
+
+  @spec parseDidMethod(String.t()) :: String.t()
+  defp parseDidMethod(did) do
+    parts = String.split(did, ":")
+    with {true, _} <- {Enum.at(parts, 0) == "did", 0},
+         {true, _} <- {String.length(Enum.at(parts, 1)) >=1, 1} do
+          {:ok, Enum.at(parts, 2)}
+         else
+          {false, 0} -> {:error, "Not a DID: #{did}"}
+          {false, 1} -> {:error, "No DID method included: #{did}"}
+    end
+  end
+end
diff --git a/lib/ex_ucan/core/structs.ex b/lib/ex_ucan/core/structs.ex
new file mode 100644
index 0000000..878848d
--- /dev/null
+++ b/lib/ex_ucan/core/structs.ex
@@ -0,0 +1,71 @@
+defmodule ExUcan.Core.Structs.UcanHeader do
+  @moduledoc """
+  Ucan header
+  """
+
+  @type t :: %__MODULE__{
+          alg: String.t(),
+          typ: String.t()
+        }
+
+  @derive Jason.Encoder
+  defstruct(
+    alg: "",
+    typ: ""
+  )
+
+end
+
+defmodule ExUcan.Core.Structs.UcanPayload do
+  @moduledoc """
+  Ucan Payload
+  """
+
+  @type t :: %__MODULE__{
+          ucv: String.t(),
+          iss: String.t(),
+          aud: String.t(),
+          nbf: integer(),
+          exp: integer(),
+          nnc: String.t(),
+          fct: map(),
+          cap: map(),
+          prf: list(String.t())
+        }
+
+  @derive Jason.Encoder
+  defstruct(
+    ucv: "",
+    iss: "",
+    aud: "",
+    nbf: 0,
+    exp: nil,
+    nnc: "",
+    fct: %{},
+    cap: %{},
+    prf: []
+  )
+end
+
+defmodule ExUcan.Core.Structs.Ucan do
+  @moduledoc """
+  UCAN struct
+  """
+  alias ExUcan.Core.Structs.UcanHeader
+  alias ExUcan.Core.Structs.UcanPayload
+
+  @type t :: %__MODULE__{
+          header: UcanHeader.t(),
+          payload: UcanPayload.t(),
+          signed_data: String.t(),
+          signature: String.t()
+        }
+
+  @derive Jason.Encoder
+  defstruct(
+    header: nil,
+    payload: nil,
+    signed_data: "",
+    signature: ""
+  )
+end
diff --git a/lib/ex_ucan/core/token.ex b/lib/ex_ucan/core/token.ex
new file mode 100644
index 0000000..f971270
--- /dev/null
+++ b/lib/ex_ucan/core/token.ex
@@ -0,0 +1,105 @@
+defmodule ExUcan.Core.Token do
+  @moduledoc """
+  Creates and manages UCAN tokens
+  """
+  alias ExUcan.Core.Structs.UcanHeader
+  alias ExUcan.Core.Keymaterial
+  alias ExUcan.Core.Structs.Ucan
+  alias ExUcan.Core.Utils
+  alias ExUcan.Core.Structs.UcanPayload
+
+  @token_type "JWT"
+  @version %{major: 0, minor: 10, patch: 0}
+
+  @spec build(params::%{
+    issuer: struct(),
+    audience: String.t(),
+    # Add capabilities struct later
+    capabilities: list(),
+    life_time_in_seconds: number(),
+    expiration: number(),
+    not_before: number(),
+    # Add Facts struct later
+    facts: list(),
+    proofs: list(String.t()),
+    add_nonce?: boolean()
+  }) :: Ucan.t()
+  def build(params) do
+    {:ok, payload} = build_payload(%{params | issuer: Keymaterial.did(params.issuer)})
+    sign_with_payload(payload, params.issuer)
+  end
+
+  # TODO: docs
+  @spec build_payload(
+          params :: %{
+            issuer: String.t(),
+            audience: String.t(),
+            # Add capabilities struct later
+            capabilities: list(),
+            life_time_in_seconds: number(),
+            expiration: number(),
+            not_before: number(),
+            # Add Facts struct later
+            facts: list(),
+            proofs: list(String.t()),
+            add_nonce?: boolean()
+          }
+        ) :: UcanPayload.t()
+  def build_payload(params) do
+    with {:iss, true} <- {:iss, String.starts_with?(params.issuer, "did")},
+         {:aud, true} <- {:aud, String.starts_with?(params.audience, "did")} do
+      current_time_in_seconds = DateTime.utc_now() |> DateTime.to_unix()
+      exp = params.expiration || current_time_in_seconds + params.life_time_in_seconds
+
+      {:ok,
+       %{
+         ucv: "#{@version.major}.#{@version.minor}.#{@version.patch}",
+         iss: params.issuer,
+         aud: params.audience,
+         nbf: params[:not_before] || nil,
+         exp: exp,
+         nnc: add_nonce(params[:add_nonce] || false),
+         fct: params[:facts] || [],
+         cap: params[:capabilities] || [],
+         prf: params[:proofs] || []
+       }}
+    else
+      {:iss, false} -> {:error, "The issuer must be a DID"}
+      {:aud, false} -> {:error, "The audience must be a DID"}
+    end
+  end
+
+  @spec encode(Ucan.t()) :: String.t()
+  def encode(%Ucan{} = ucan) do
+    "#{ucan.signed_data}.#{ucan.signature}"
+  end
+
+  defp add_nonce(true), do: Utils.generate_nonce()
+  defp add_nonce(false), do: nil
+
+  @spec sign_with_payload(payload :: UcanPayload.t(), keypair :: struct()) :: Ucan.t()
+  defp sign_with_payload(payload, keypair) do
+
+    # TODO ExUcan.Core.Plugins.verify_issuer_alg
+    header = %UcanHeader{alg: keypair.jwt_alg, typ: @token_type}
+    encoded_header = encode_ucan_parts(header)
+    encoded_payload = encode_ucan_parts(payload)
+
+    signed_data = "#{encoded_header}.#{encoded_payload}"
+    signature = Keymaterial.sign(keypair, signed_data)
+    %Ucan{
+      header: header,
+      payload: payload,
+      signed_data: signed_data,
+      signature: Base.url_encode64(signature, padding: false)
+    }
+  end
+
+  @spec encode_ucan_parts(UcanHeader.t() | UcanPayload.t()) :: String.t()
+  defp encode_ucan_parts(data) do
+    data
+    |> Jason.encode!()
+    |> Base.url_encode64(padding: false)
+  end
+
+end
diff --git a/lib/ex_ucan/core/utils.ex b/lib/ex_ucan/core/utils.ex
new file mode 100644
index 0000000..f392ff9
--- /dev/null
+++ b/lib/ex_ucan/core/utils.ex
@@ -0,0 +1,15 @@
+defmodule ExUcan.Core.Utils do
+  @moduledoc """
+  Core utils
+  """
+  @chars "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+  # TODO: docs
+  def generate_nonce(len \\ 6)
+
+  def generate_nonce(len) do
+    Enum.reduce(1..len, "", fn _, nonce ->
+      nonce <> String.at(@chars, :rand.uniform(String.length(@chars) - 1))
+    end)
+  end
+end
diff --git a/lib/ex_ucan/plugins/ed25519/keypair.ex b/lib/ex_ucan/plugins/ed25519/keypair.ex
index 6c39a8f..2af4062 100644
--- a/lib/ex_ucan/plugins/ed25519/keypair.ex
+++ b/lib/ex_ucan/plugins/ed25519/keypair.ex
@@ -2,7 +2,9 @@ defmodule ExUcan.Plugins.Ed25519.Keypair do
   @moduledoc """
   Encapsulates Ed25519 Keypair generation and other utilities
   """
+  alias ExUcan.Core.Keymaterial
   alias ExUcan.Plugins.Ed25519.Crypto
+  @behaviour Keymaterial
   # TODO: more doc..
 
   # TODO: Need type doc
@@ -25,17 +27,21 @@ defmodule ExUcan.Plugins.Ed25519.Keypair do
 
   def create(exportable?) do
     {pub, priv} = :crypto.generate_key(:eddsa, :ed25519)
-
-    __MODULE__.__struct__(
+    %__MODULE__{
       jwt_alg: "EdDSA",
       secret_key: priv,
       public_key: pub,
       exportable: exportable?
-    )
+    }
   end
 
-  @spec did(__MODULE__.t()) :: String.t()
-  def did(keypair) do
-    Crypto.publickey_to_did(keypair.public_key)
+  defimpl Keymaterial do
+    def did(keypair) do
+      Crypto.publickey_to_did(keypair.public_key)
+    end
+
+    def sign(keypair, payload) do
+      :public_key.sign(payload, :ignored, {:ed_pri, :ed25519, keypair.public_key, keypair.secret_key}, [])
+    end
   end
 end
diff --git a/lib/ex_ucan/plugins/protocols.ex b/lib/ex_ucan/plugins/protocols.ex
deleted file mode 100644
index aaa2c54..0000000
--- a/lib/ex_ucan/plugins/protocols.ex
+++ /dev/null
@@ -1,5 +0,0 @@
-# TODO: docs??
-
-defprotocol ExUcan.Plugins.Protocols.Keygen do
-  def create(type)
-end