refactor otp

app/controllers/submit_form_email_2fas_controller.rb

@@ -10,12 +10,10 @@ class SubmitFormEmail2fasController < ApplicationController
 
   def create
     RateLimit.call("verify-2fa-code-#{@submitter.id}", limit: 2, ttl: 45.seconds, enabled: true)
-    RateLimit.call("verify-2fa-code-1h-#{@submitter.id}", limit: 10, ttl: 1.hour, enabled: true)
-    RateLimit.call("verify-2fa-code-1d-#{@submitter.id}", limit: 20, ttl: 1.day, enabled: true)
 
-    value = [@submitter.email.downcase.strip, @submitter.slug].join(':')
+    value = [@submitter.email.downcase.squish, @submitter.slug].join(':')
 
-    if EmailVerificationCodes.verify(params[:one_time_code].to_s.gsub(/\D/, ''), value)
+    if OtpChallenges.verify(params[:one_time_code].to_s.gsub(/\D/, ''), value, purpose: 'form_email_2fa')
       SubmissionEvents.create_with_tracking_data(@submitter, 'email_verified', request, { email: @submitter.email })
 
       cookies.encrypted[:email_2fa_slug] =

app/mailers/submitter_mailer.rb

@@ -181,7 +181,8 @@ class SubmitterMailer < ApplicationMailer
   def otp_verification_email(submitter, locale: nil)
     @current_account = submitter.account
     @submitter = submitter
-    @otp_code = EmailVerificationCodes.generate([submitter.email.downcase.strip, submitter.slug].join(':'))
+    @otp_code = OtpChallenges.generate([submitter.email.downcase.squish, submitter.slug].join(':'),
+                                       purpose: 'form_email_2fa')
 
     assign_message_metadata('otp_verification_email', submitter)
 

app/mailers/template_mailer.rb

@@ -5,7 +5,7 @@ class TemplateMailer < ApplicationMailer
     @current_account = template.account
     @template = template
 
-    @otp_code = EmailVerificationCodes.generate([email.downcase.strip, template.slug].join(':'))
+    @otp_code = OtpChallenges.generate([email.downcase.squish, template.slug].join(':'), purpose: 'form_email_2fa')
 
     assign_message_metadata('otp_verification_email', template)
 

app/models/otp_challenge.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: otp_challenges
+#
+#  id          :bigint           not null, primary key
+#  attempts    :integer          default(0), not null
+#  expire_at   :datetime         not null
+#  key         :string           not null
+#  nonce       :string           not null
+#  verified_at :datetime
+#  version     :integer          not null
+#  created_at  :datetime         not null
+#
+# Indexes
+#
+#  index_otp_challenges_on_key_and_version  (key,version) UNIQUE
+#
+class OtpChallenge < ApplicationRecord
+end

db/migrate/20260930061927_create_otp_challenges.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class CreateOtpChallenges < ActiveRecord::Migration[8.1]
+  def change
+    create_table :otp_challenges do |t|
+      t.string :key, null: false
+      t.integer :version, null: false
+      t.string :nonce, null: false
+      t.integer :attempts, null: false, default: 0
+      t.datetime :expire_at, null: false
+      t.datetime :verified_at
+      t.datetime :created_at, null: false
+
+      t.index %i[key version], unique: true
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_08_19_091500) do
+ActiveRecord::Schema[8.1].define(version: 2026_09_30_061927) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "btree_gin"
   enable_extension "pg_catalog.plpgsql"
@@ -322,6 +322,17 @@ ActiveRecord::Schema[8.1].define(version: 2026_08_19_091500) do
     t.index ["uid"], name: "index_oauth_applications_on_uid", unique: true
   end
 
+  create_table "otp_challenges", force: :cascade do |t|
+    t.integer "attempts", default: 0, null: false
+    t.datetime "created_at", null: false
+    t.datetime "expire_at", null: false
+    t.string "key", null: false
+    t.string "nonce", null: false
+    t.datetime "verified_at"
+    t.integer "version", null: false
+    t.index ["key", "version"], name: "index_otp_challenges_on_key_and_version", unique: true
+  end
+
   create_table "search_entries", force: :cascade do |t|
     t.bigint "account_id", null: false
     t.datetime "created_at", null: false

lib/email_verification_codes.rb

@@ -1,27 +0,0 @@
-# frozen_string_literal: true
-
-module EmailVerificationCodes
-  DRIFT_BEHIND = 5.minutes
-
-  module_function
-
-  def generate(value)
-    totp = ROTP::TOTP.new(build_totp_secret(value))
-
-    totp.at(Time.current)
-  end
-
-  def verify(code, value)
-    totp = ROTP::TOTP.new(build_totp_secret(value))
-
-    totp.verify(code, drift_behind: DRIFT_BEHIND)
-  end
-
-  def build_totp_secret(value)
-    ROTP::Base32.encode(
-      Digest::SHA1.digest(
-        [Rails.application.secret_key_base, 'form_email_2fa', value].join(':')
-      )
-    )
-  end
-end

lib/otp_challenges.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+module OtpChallenges
+  CODE_TTL = 10.minutes
+  REUSE_MIN_TTL = 5.minutes
+  MAX_ATTEMPTS = 20
+  MAX_TOTAL_ATTEMPTS = 100
+  ATTEMPTS_WINDOW = 23.hours
+
+  module_function
+
+  def generate(value, purpose:)
+    key = build_key(value, purpose)
+    latest_challenge = OtpChallenge.where(key:).order(version: :desc).first
+
+    otp_challenge =
+      if latest_challenge && !latest_challenge.verified_at? && latest_challenge.expire_at > REUSE_MIN_TTL.from_now
+        latest_challenge
+      else
+        version = latest_challenge ? latest_challenge.version + 1 : 1
+
+        OtpChallenge.create_with(nonce: SecureRandom.base58(16), expire_at: CODE_TTL.from_now)
+                    .create_or_find_by!(key:, version:)
+      end
+
+    build_hotp(value, purpose, otp_challenge.nonce).at(0)
+  end
+
+  def verify(code, value, purpose:)
+    challenges = OtpChallenge.where(key: build_key(value, purpose))
+
+    recent_challenges = challenges.where(expire_at: ATTEMPTS_WINDOW.ago..).order(version: :desc).to_a
+
+    latest_challenge = recent_challenges.first
+
+    return false if latest_challenge.nil? || latest_challenge.verified_at? || latest_challenge.expire_at.past?
+
+    raise RateLimit::LimitApproached if recent_challenges.sum(&:attempts) >= MAX_ATTEMPTS
+    raise RateLimit::LimitApproached if challenges.sum(:attempts) >= MAX_TOTAL_ATTEMPTS
+
+    if build_hotp(value, purpose, latest_challenge.nonce).verify(code.to_s, 0)
+      OtpChallenge.where(id: latest_challenge.id, verified_at: nil).update_all(verified_at: Time.current) == 1
+    else
+      latest_challenge.increment!(:attempts)
+
+      OtpChallenge.current_transaction.after_rollback { OtpChallenge.update_counters(latest_challenge.id, attempts: 1) }
+
+      false
+    end
+  end
+
+  def build_key(value, purpose)
+    Digest::SHA256.hexdigest([purpose, value].join(':'))
+  end
+
+  def build_hotp(value, purpose, nonce)
+    ROTP::HOTP.new(
+      ROTP::Base32.encode(
+        Digest::SHA1.digest([Rails.application.secret_key_base, purpose, value, nonce].join(':'))
+      )
+    )
+  end
+end

lib/submitters.rb

@@ -280,12 +280,12 @@ module Submitters
     email_digest = Digest::MD5.base64digest(submitter.email.downcase.squish)
 
     RateLimit.call("verify-2fa-code-#{email_digest}", limit: 2, ttl: 45.seconds, enabled: true)
-    RateLimit.call("verify-2fa-code-1h-#{email_digest}", limit: 10, ttl: 1.hour, enabled: true)
-    RateLimit.call("verify-2fa-code-1d-#{email_digest}", limit: 20, ttl: 1.day, enabled: true)
 
     link_2fa_key = [submitter.email.downcase.squish, submitter.submission.template.slug].join(':')
 
-    raise InvalidOtp, I18n.t(:invalid_code) unless EmailVerificationCodes.verify(otp, link_2fa_key)
+    unless OtpChallenges.verify(otp.to_s.gsub(/\D/, ''), link_2fa_key, purpose: 'form_email_2fa')
+      raise InvalidOtp, I18n.t(:invalid_code)
+    end
 
     true
   end