diff --git a/test/test_orm_encryption_rotation.rb b/test/test_orm_encryption_rotation.rb
new file mode 100644
index 0000000..1bbf9e1
--- /dev/null
+++ b/test/test_orm_encryption_rotation.rb
@@ -0,0 +1,159 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+
+# Key rotation for Prism::Orm::Encryption: retiring an application secret
+# (a suspected leak, a scheduled policy) should not make every already-
+# encrypted row unreadable the moment the new secret goes live. These tests
+# encrypt a row under an OLD secret, then simulate the moment of rotation
+# (primary_key flips to a new secret, the old one moves to previous_keys),
+# and check that reads/queries against the old row keep working while
+# writes immediately start using the new key.
+class OrmEncryptionRotationTest < Minitest::Test
+  OLD_SECRET = 'rotation-old-secret-do-not-use-in-prod'.freeze
+  NEW_SECRET = 'rotation-new-secret-do-not-use-in-prod'.freeze
+
+  def setup
+    @dir = Dir.mktmpdir('prism-encryption-rotation-store')
+    @store = Prism::Orm::Store.new(File.join(@dir, 'test.pstore'))
+    @store.create_table(:patients, %w[id name ssn notes])
+  end
+
+  def teardown
+    FileUtils.remove_entry(@dir)
+    Prism::Orm::Encryption.primary_key = nil
+    Prism::Orm::Encryption.previous_keys = []
+    Object.send(:remove_const, :RotatingPatient) if Object.const_defined?(:RotatingPatient)
+  end
+
+  def define_patient_class
+    klass = Class.new(Prism::Orm::Model) do
+      table_name :patients
+      encrypts :ssn, deterministic: true
+      encrypts :notes
+    end
+    klass.store = @store
+    Object.const_set(:RotatingPatient, klass)
+    klass
+  end
+
+  def test_a_row_encrypted_under_the_old_key_is_unreadable_without_rotation_configured
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    old_class = define_patient_class
+    patient = old_class.create!(name: 'Alice', ssn: '123-45-6789', notes: 'pre-rotation note')
+
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    new_class = define_patient_class
+
+    error = assert_raises(Prism::Orm::Encryption::Error) { new_class.find(patient.id).notes }
+    assert_match(/wrong key/, error.message)
+  end
+
+  def test_a_row_encrypted_under_the_old_key_stays_readable_once_rotation_is_configured
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    old_class = define_patient_class
+    patient = old_class.create!(name: 'Alice', ssn: '123-45-6789', notes: 'pre-rotation note')
+
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    Prism::Orm::Encryption.previous_keys = [OLD_SECRET]
+    new_class = define_patient_class
+
+    reloaded = new_class.find(patient.id)
+    assert_equal '123-45-6789', reloaded.ssn
+    assert_equal 'pre-rotation note', reloaded.notes
+  end
+
+  def test_a_row_re_saved_after_rotation_is_re_encrypted_under_the_new_key
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    old_class = define_patient_class
+    patient = old_class.create!(name: 'Alice', ssn: '123-45-6789', notes: 'pre-rotation note')
+
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    Prism::Orm::Encryption.previous_keys = [OLD_SECRET]
+    new_class = define_patient_class
+
+    record = new_class.find(patient.id)
+    record.notes = 'still the same note, just re-saved'
+    record.save!
+
+    # Once re-saved, the OLD key alone (rotation not configured on THIS
+    # class) must no longer be able to decrypt it - proving the write path
+    # switched to the new key rather than continuing to use whichever key
+    # happened to work on read.
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    Prism::Orm::Encryption.previous_keys = []
+    old_key_only_class = define_patient_class
+    error = assert_raises(Prism::Orm::Encryption::Error) { old_key_only_class.find(patient.id).notes }
+    assert_match(/wrong key/, error.message)
+  end
+
+  def test_where_on_a_deterministic_column_finds_rows_encrypted_under_either_key
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    old_class = define_patient_class
+    stale = old_class.create!(name: 'Stale', ssn: '555-55-5555', notes: 'n')
+
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    Prism::Orm::Encryption.previous_keys = [OLD_SECRET]
+    new_class = define_patient_class
+    fresh = new_class.create!(name: 'Fresh', ssn: '555-55-5555', notes: 'n')
+
+    found = new_class.where(ssn: '555-55-5555').to_a.map(&:id).sort
+    assert_equal [stale.id, fresh.id].sort, found
+  end
+
+  def test_find_by_on_a_deterministic_column_matches_a_row_still_encrypted_under_the_old_key
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    old_class = define_patient_class
+    stale = old_class.create!(name: 'Stale', ssn: '999-99-9999', notes: 'n')
+
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    Prism::Orm::Encryption.previous_keys = [OLD_SECRET]
+    new_class = define_patient_class
+
+    found = new_class.find_by(ssn: '999-99-9999')
+    assert_equal stale.id, found.id
+  end
+
+  def test_per_attribute_previous_keys_overrides_the_global_rotation_list
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    Prism::Orm::Encryption.previous_keys = ['a-secret-that-was-never-used']
+
+    scoped_old_class = Class.new(Prism::Orm::Model) do
+      table_name :patients
+      encrypts :notes, key: OLD_SECRET
+    end
+    scoped_old_class.store = @store
+    patient = scoped_old_class.create!(name: 'Alice', notes: 'scoped secret note')
+
+    scoped_new_class = Class.new(Prism::Orm::Model) do
+      table_name :patients
+      encrypts :notes, key: NEW_SECRET, previous_keys: [OLD_SECRET]
+    end
+    scoped_new_class.store = @store
+
+    assert_equal 'scoped secret note', scoped_new_class.find(patient.id).notes
+  end
+
+  def test_a_tampered_ciphertext_still_raises_even_with_rotation_configured
+    Prism::Orm::Encryption.primary_key = OLD_SECRET
+    old_class = define_patient_class
+    patient = old_class.create!(name: 'Alice', ssn: '123-45-6789', notes: 'note')
+    row = @store.find(:patients, patient.id)
+    tampered = row.dup
+    tampered['notes'] = row['notes'].sub(/^./) { |c| c == 'A' ? 'B' : 'A' }
+    @store.update(:patients, patient.id, tampered)
+
+    Object.send(:remove_const, :RotatingPatient)
+    Prism::Orm::Encryption.primary_key = NEW_SECRET
+    Prism::Orm::Encryption.previous_keys = [OLD_SECRET]
+    new_class = define_patient_class
+
+    assert_raises(Prism::Orm::Encryption::Error) { new_class.find(patient.id).notes }
+  end
+end