diff --git a/internal/config/config.go b/internal/config/config.go
new file mode 100644
index 0000000..1c5ac82
--- /dev/null
+++ b/internal/config/config.go
@@ -0,0 +1,8 @@
+package config
+
+type Config struct {
+	PublicKeyPath  string
+	PrivateKeyPath string
+}
+
+var Default = Config{}
diff --git a/internal/db/db.go b/internal/db/db.go
new file mode 100644
index 0000000..9d65db0
--- /dev/null
+++ b/internal/db/db.go
@@ -0,0 +1,19 @@
+package db
+
+import "github.com/AYM1607/ccclip/pkg/api"
+
+type DB interface {
+	// Users.
+	PutUser(id string, passwordHash string) error
+	GetUser(id string) (*api.User, error)
+
+	// Devices.
+	PutDevice(pubKey, userId string) (string, error)
+	GetDevice(id string) (*api.Device, error)
+	GetUserDevices(userId string) ([]*api.Device, error)
+	GetDeviceUser(deviceId string) (*api.User, error)
+
+	// Clipboard.
+	PutClipboard(userId string, clipboard *api.Clipboard) error
+	GetClipboard(userId string) (*api.Clipboard, error)
+}
diff --git a/internal/db/local.go b/internal/db/local.go
new file mode 100644
index 0000000..840d699
--- /dev/null
+++ b/internal/db/local.go
@@ -0,0 +1,106 @@
+package db
+
+import (
+	"errors"
+	"fmt"
+
+	ulid "github.com/oklog/ulid/v2"
+
+	"github.com/AYM1607/ccclip/pkg/api"
+)
+
+type localDB struct {
+	users        map[string]*api.User
+	devices      map[string]*api.Device
+	usersDevices map[string]map[string]struct{}
+	clipboards   map[string]*api.Clipboard
+}
+
+var _ DB = (*localDB)(nil)
+
+func NewLocalDB() DB {
+	return &localDB{
+		users:        make(map[string]*api.User),
+		devices:      make(map[string]*api.Device),
+		usersDevices: make(map[string]map[string]struct{}),
+		clipboards:   make(map[string]*api.Clipboard),
+	}
+}
+
+func (d *localDB) PutUser(id, passwordHash string) error {
+	if _, ok := d.users[id]; ok {
+		return errors.New("user exists")
+	}
+	d.users[id] = &api.User{ID: id, PasswordHash: passwordHash}
+	return nil
+}
+
+func (d *localDB) GetUser(id string) (*api.User, error) {
+	u, ok := d.users[id]
+	if !ok {
+		return nil, errors.New("user does not exist")
+	}
+	return u, nil
+}
+
+func (d *localDB) PutDevice(pubKey, userId string) (string, error) {
+	id := ulid.Make().String()
+	if _, ok := d.users[userId]; !ok {
+		return "", errors.New("user does not exist")
+	}
+
+	d.devices[id] = &api.Device{
+		ID:        id,
+		PublicKey: pubKey,
+	}
+
+	if d.usersDevices[userId] == nil {
+		d.usersDevices[userId] = map[string]struct{}{}
+	}
+	d.usersDevices[userId][id] = struct{}{}
+	return id, nil
+}
+
+func (d *localDB) GetDevice(id string) (*api.Device, error) {
+	device, ok := d.devices[id]
+	if !ok {
+		return nil, errors.New("requested device does no exist")
+	}
+	return device, nil
+}
+
+func (d *localDB) GetUserDevices(userId string) ([]*api.Device, error) {
+	ids := d.usersDevices[userId]
+	res := []*api.Device{}
+	for id := range ids {
+		d, ok := d.devices[id]
+		if !ok {
+			return nil, fmt.Errorf("device %s is associated to user but it does not exist", id)
+		}
+		res = append(res, d)
+	}
+	return res, nil
+}
+
+func (d *localDB) GetDeviceUser(deviceId string) (*api.User, error) {
+	// Foreign keys can make this better.
+	for uId, u := range d.users {
+		if _, ok := d.usersDevices[uId]; ok {
+			return u, nil
+		}
+	}
+	return nil, errors.New("device is not associated to any user")
+}
+
+func (d *localDB) PutClipboard(userId string, clipboard *api.Clipboard) error {
+	d.clipboards[userId] = clipboard
+	return nil
+}
+
+func (d *localDB) GetClipboard(userId string) (*api.Clipboard, error) {
+	c, ok := d.clipboards[userId]
+	if !ok {
+		return nil, errors.New("user does not have a current clipboard")
+	}
+	return c, nil
+}
diff --git a/pkg/api/api.go b/pkg/api/api.go
new file mode 100644
index 0000000..3772e07
--- /dev/null
+++ b/pkg/api/api.go
@@ -0,0 +1,17 @@
+package api
+
+type User struct {
+	ID           string
+	PasswordHash string
+}
+
+type Device struct {
+	ID        string
+	PublicKey []byte
+}
+
+type Clipboard struct {
+	SenderDeviceID string
+	// Payloads maps DeviceIDs to base64 encoded data.
+	Payloads map[string]string
+}