diff --git a/docs/utilities.md b/docs/utilities.md
index 0a200fdf..69181641 100644
--- a/docs/utilities.md
+++ b/docs/utilities.md
@@ -476,6 +476,13 @@ encoding = require "lapis.util.encoding"
 ]]
 }
 
+Inside OpenResty, `encode_base64`, `decode_base64` and `hmac_sha1` use the
+implementations built into `ngx`. Any other HMAC is calculated with
+[luaossl](https://github.com/wahern/luaossl), or with
+[lua-resty-openssl](https://github.com/fffonion/lua-resty-openssl) when luaossl
+can't be loaded. Without either library the module still loads, but
+calculating that HMAC raises an error.
+
 ### `encode_base64(str)`
 
 Base64 encodes a string.
@@ -614,7 +621,9 @@ to have it encoded into the token. You can then use the `callback` parameter of
 `validate_token` to verify data's value.
 
 The random string is stored in a cookie named as your session name with
-`_token` appended to the end.
+`_token` appended to the end. Its random bytes come from luaossl. Inside
+OpenResty, the `resty.random` module that ships with OpenResty is used when
+luaossl can't be loaded.
 
 ### `csrf.validate_token(req, callback=nil)`
 
diff --git a/lapis/csrf.lua b/lapis/csrf.lua
index 74f504fd..c22f2bad 100644
--- a/lapis/csrf.lua
+++ b/lapis/csrf.lua
@@ -3,14 +3,34 @@ do
   local _obj_0 = require("lapis.util.encoding")
   encode_base64, encode_with_secret, decode_with_secret = _obj_0.encode_base64, _obj_0.encode_with_secret, _obj_0.decode_with_secret
 end
-local openssl_rand = require("openssl.rand")
 local config = require("lapis.config").get()
 local cookie_name = tostring(config.session_name) .. "_token"
+local random_bytes
+do
+  local has_luaossl, openssl_rand = pcall(require, "openssl.rand")
+  if has_luaossl then
+    random_bytes = openssl_rand.bytes
+  elseif ngx and ngx.config and pcall(function()
+    return require("resty.random")
+  end) then
+    local resty_random = require("resty.random")
+    random_bytes = function(n)
+      local bytes = resty_random.bytes(n, true)
+      assert(bytes, "lapis.csrf: resty.random failed to generate random bytes")
+      return bytes
+    end
+  else
+    local luaossl_err = openssl_rand
+    random_bytes = function()
+      return error("lapis.csrf: generating a token requires luaossl (or resty.random in OpenResty), but luaossl failed to load: " .. tostring(luaossl_err))
+    end
+  end
+end
 local generate_token
 generate_token = function(req, data)
   local key = req.cookies[cookie_name]
   if not (key) then
-    key = encode_base64(openssl_rand.bytes(32))
+    key = encode_base64(random_bytes(32))
     req.cookies[cookie_name] = key
   end
   local token = {
diff --git a/lapis/csrf.moon b/lapis/csrf.moon
index 64323c82..102918f4 100644
--- a/lapis/csrf.moon
+++ b/lapis/csrf.moon
@@ -1,16 +1,35 @@
 -- csrf protection
 
 import encode_base64, encode_with_secret, decode_with_secret from require "lapis.util.encoding"
-openssl_rand = require "openssl.rand"
 
 config = require"lapis.config".get!
 cookie_name = "#{config.session_name}_token"
 
+-- luaossl is optional so it doesn't have to be installed for apps running in
+-- OpenResty, which bundles resty.random. resty.random calls into the OpenSSL
+-- that nginx is linked with, so it's only used inside of a real nginx process.
+-- (The fake ngx of a simulated request has no ngx.config)
+random_bytes = do
+  has_luaossl, openssl_rand = pcall require, "openssl.rand"
+
+  if has_luaossl
+    openssl_rand.bytes
+  elseif ngx and ngx.config and pcall -> require "resty.random"
+    resty_random = require "resty.random"
+    (n) ->
+      bytes = resty_random.bytes n, true
+      assert bytes, "lapis.csrf: resty.random failed to generate random bytes"
+      bytes
+  else
+    luaossl_err = openssl_rand
+    ->
+      error "lapis.csrf: generating a token requires luaossl (or resty.random in OpenResty), but luaossl failed to load: #{luaossl_err}"
+
 generate_token = (req, data) ->
   key = req.cookies[cookie_name]
 
   unless key
-    key = encode_base64 openssl_rand.bytes(32)
+    key = encode_base64 random_bytes 32
     req.cookies[cookie_name] = key
 
   token = {
diff --git a/lapis/util/encoding.lua b/lapis/util/encoding.lua
index e34bd206..a09e978a 100644
--- a/lapis/util/encoding.lua
+++ b/lapis/util/encoding.lua
@@ -1,6 +1,28 @@
 local encode_base64, decode_base64, hmac_sha1
 local config = require("lapis.config").get()
-local openssl_hmac = require("openssl.hmac")
+local new_hmac
+do
+  local has_luaossl, openssl_hmac = pcall(require, "openssl.hmac")
+  if has_luaossl then
+    new_hmac = openssl_hmac.new
+  elseif pcall(function()
+    return require("resty.openssl.hmac")
+  end) then
+    new_hmac = require("resty.openssl.hmac").new
+  else
+    local luaossl_err = openssl_hmac
+    new_hmac = function(secret, digest_type)
+      return error("lapis.util.encoding: hmac_" .. tostring(digest_type) .. " requires luaossl or lua-resty-openssl, but luaossl failed to load: " .. tostring(luaossl_err))
+    end
+  end
+end
+local hmac_for
+hmac_for = function(digest_type)
+  return function(secret, str)
+    local hmac = assert(new_hmac(secret, digest_type))
+    return assert(hmac:final(str))
+  end
+end
 if ngx then
   do
     local _obj_0 = ngx
@@ -16,16 +38,9 @@ else
   decode_base64 = function(...)
     return (unb64(...))
   end
-  hmac_sha1 = function(secret, str)
-    local hmac = openssl_hmac.new(secret, "sha1")
-    return hmac:final(str)
-  end
-end
-local hmac_sha256
-hmac_sha256 = function(secret, str)
-  local hmac = openssl_hmac.new(secret, "sha256")
-  return hmac:final(str)
+  hmac_sha1 = hmac_for("sha1")
 end
+local hmac_sha256 = hmac_for("sha256")
 local default_hmac
 local _exp_0 = config.hmac_digest
 if "sha256" == _exp_0 then
diff --git a/lapis/util/encoding.moon b/lapis/util/encoding.moon
index 4b195027..6782d167 100644
--- a/lapis/util/encoding.moon
+++ b/lapis/util/encoding.moon
@@ -2,7 +2,27 @@
 local encode_base64, decode_base64, hmac_sha1
 
 config = require"lapis.config".get!
-openssl_hmac = require "openssl.hmac"
+
+-- luaossl is optional so it doesn't have to be installed for apps running in
+-- OpenResty, where lua-resty-openssl can be used instead. Both libraries
+-- provide new(key, digest_type) to create an hmac. With neither installed,
+-- calculating an hmac raises an error that includes why luaossl failed to load
+new_hmac = do
+  has_luaossl, openssl_hmac = pcall require, "openssl.hmac"
+
+  if has_luaossl
+    openssl_hmac.new
+  elseif pcall -> require "resty.openssl.hmac"
+    require("resty.openssl.hmac").new
+  else
+    luaossl_err = openssl_hmac
+    (secret, digest_type) ->
+      error "lapis.util.encoding: hmac_#{digest_type} requires luaossl or lua-resty-openssl, but luaossl failed to load: #{luaossl_err}"
+
+hmac_for = (digest_type) ->
+  (secret, str) ->
+    hmac = assert new_hmac secret, digest_type
+    assert hmac\final str
 
 if ngx
   {:encode_base64, :decode_base64, :hmac_sha1} = ngx
@@ -12,17 +32,13 @@ else
   encode_base64 = (...) -> (b64 ...)
   decode_base64 = (...) -> (unb64 ...)
 
-  hmac_sha1 = (secret, str) ->
-    hmac = openssl_hmac.new secret, "sha1"
-    hmac\final str
+  hmac_sha1 = hmac_for "sha1"
 
 ---Generate HMAC-SHA256 hash
 ---@param secret string Secret key for HMAC
 ---@param str string String to hash
 ---@return string hash Binary HMAC-SHA256 digest
-hmac_sha256 = (secret, str) ->
-  hmac = openssl_hmac.new secret, "sha256"
-  hmac\final str
+hmac_sha256 = hmac_for "sha256"
 
 default_hmac = switch config.hmac_digest
   when "sha256"
diff --git a/spec/csrf_spec.moon b/spec/csrf_spec.moon
index 2a0e6996..e970ecac 100644
--- a/spec/csrf_spec.moon
+++ b/spec/csrf_spec.moon
@@ -1,5 +1,7 @@
 csrf = require "lapis.csrf"
-import encode_with_secret, decode_with_secret from require "lapis.util.encoding"
+import encode_base64, encode_with_secret, decode_with_secret from require "lapis.util.encoding"
+ngx_stack = require "lapis.spec.stack"
+import require_with_stubs from require "spec.helpers"
 
 describe "lapis.csrf", ->
   config = require"lapis.config".get!
@@ -192,3 +194,90 @@ describe "lapis.csrf", ->
           csrf_token: token
         }
       }, (d) -> d.number == 5
+
+  describe "random bytes backend", ->
+    -- stands in for luaossl's openssl.rand and OpenResty's resty.random
+    fake_rand = (char, log) -> {
+      bytes: (n, strong) ->
+        table.insert log, { :n, :strong } if log
+        string.rep char, n
+    }
+
+    generate_key = (c) ->
+      r = { cookies: {} }
+      assert c.generate_token r
+      r.cookies.lapis_session_token
+
+    it "uses luaossl when it's installed", ->
+      ngx_stack.push { config: {} }
+      finally -> ngx_stack.pop!
+
+      c = require_with_stubs "lapis.csrf", {
+        "openssl.rand": fake_rand "a"
+        "resty.random": fake_rand "b"
+      }
+
+      assert.same encode_base64(string.rep "a", 32), generate_key c
+
+    it "falls back to resty.random with nginx", ->
+      ngx_stack.push { config: {} }
+      finally -> ngx_stack.pop!
+
+      calls = {}
+      c = require_with_stubs "lapis.csrf", {
+        "openssl.rand": false
+        "resty.random": fake_rand "b", calls
+      }
+
+      assert.same encode_base64(string.rep "b", 32), generate_key c
+      -- asks for cryptographically strong bytes
+      assert.same {{ n: 32, strong: true }}, calls
+
+    it "fails when resty.random can't generate bytes", ->
+      ngx_stack.push { config: {} }
+      finally -> ngx_stack.pop!
+
+      c = require_with_stubs "lapis.csrf", {
+        "openssl.rand": false
+        "resty.random": { bytes: -> nil }
+      }
+
+      ok, err = pcall generate_key, c
+      assert.same false, ok
+      assert.truthy err\find "resty.random failed to generate random bytes", 1, true
+
+    describe "without nginx", ->
+      assert_no_backend = ->
+        c = require_with_stubs "lapis.csrf", {
+          "openssl.rand": false
+          "resty.random": fake_rand "b"
+        }
+
+        ok, err = pcall generate_key, c
+        assert.same false, ok
+        assert.truthy err\find "generating a token requires luaossl (or resty.random in OpenResty)", 1, true
+        -- includes the reason luaossl couldn't be loaded
+        assert.truthy err\find "luaossl failed to load: module 'openssl.rand' not found (stubbed by spec)", 1, true
+
+      it "fails to generate a token without luaossl", ->
+        assert_no_backend!
+
+      it "doesn't use resty.random in a simulated request", ->
+        -- the fake ngx of a simulated request has no ngx.config
+        ngx_stack.push { _lapis_simulate: true }
+        finally -> ngx_stack.pop!
+        assert_no_backend!
+
+    it "validates tokens without a backend", ->
+      c = require_with_stubs "lapis.csrf", {
+        "openssl.rand": false
+        "resty.random": false
+      }
+
+      r = { cookies: {} }
+      token = csrf.generate_token r
+
+      assert c.validate_token {
+        cookies: r.cookies
+        params: { csrf_token: token }
+      }
diff --git a/spec/encoding_spec.moon b/spec/encoding_spec.moon
index f473a546..730f1118 100644
--- a/spec/encoding_spec.moon
+++ b/spec/encoding_spec.moon
@@ -1,4 +1,16 @@
 encoding = require "lapis.util.encoding"
+ngx_stack = require "lapis.spec.stack"
+import require_with_stubs from require "spec.helpers"
+
+to_hex = (str) -> (str\gsub ".", (c) -> string.format "%02x", c\byte!)
+
+-- stands in for luaossl's openssl.hmac and lua-resty-openssl's
+-- resty.openssl.hmac, which share the same interface
+fake_hmac = (name) -> {
+  new: (secret, digest_type) -> {
+    final: (str) => "#{name}:#{digest_type}:#{secret}:#{str}"
+  }
+}
 
 describe "lapis.util.encoding", ->
   config = require"lapis.config".get!
@@ -29,4 +41,84 @@ describe "lapis.util.encoding", ->
     assert.same {encoding.decode_with_secret "hello.world"},
       {nil, "invalid signature"}
 
+  -- RFC 2202 and RFC 4231 test case 2
+  it "calculates hmac_sha1", ->
+    assert.same "effcdf6ae5eb2fa2d27416d5f184df9c259a7c79",
+      to_hex encoding.hmac_sha1 "Jefe", "what do ya want for nothing?"
+
+  it "calculates hmac_sha256", ->
+    assert.same "5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843",
+      to_hex encoding.hmac_sha256 "Jefe", "what do ya want for nothing?"
+
+  describe "hmac backend", ->
+    it "uses luaossl when it's installed", ->
+      e = require_with_stubs "lapis.util.encoding", {
+        "openssl.hmac": fake_hmac "luaossl"
+        "resty.openssl.hmac": fake_hmac "resty"
+      }
+
+      assert.same "luaossl:sha1:key:msg", e.hmac_sha1 "key", "msg"
+      assert.same "luaossl:sha256:key:msg", e.hmac_sha256 "key", "msg"
+
+    it "falls back to lua-resty-openssl", ->
+      e = require_with_stubs "lapis.util.encoding", {
+        "openssl.hmac": false
+        "resty.openssl.hmac": fake_hmac "resty"
+      }
+
+      assert.same "resty:sha1:key:msg", e.hmac_sha1 "key", "msg"
+      assert.same "resty:sha256:key:msg", e.hmac_sha256 "key", "msg"
+
+    it "loads without a backend and fails when an hmac is calculated", ->
+      e = require_with_stubs "lapis.util.encoding", {
+        "openssl.hmac": false
+        "resty.openssl.hmac": false
+      }
+
+      for fn_name in *{"hmac_sha1", "hmac_sha256"}
+        ok, err = pcall e[fn_name], "key", "msg"
+        assert.same false, ok
+        assert.truthy err\find "#{fn_name} requires luaossl or lua-resty-openssl", 1, true
+        -- includes the reason luaossl couldn't be loaded
+        assert.truthy err\find "luaossl failed to load: module 'openssl.hmac' not found (stubbed by spec)", 1, true
+
+      assert.has_error -> e.encode_with_secret { color: "red" }
+
+    describe "with nginx", ->
+      before_each ->
+        mime = require "mime"
+        ngx_stack.push {
+          config: {}
+          encode_base64: (str) -> (mime.b64 str)
+          decode_base64: (str) -> (mime.unb64 str)
+          hmac_sha1: (secret, str) -> "ngx:sha1:#{secret}:#{str}"
+        }
+
+      after_each ->
+        ngx_stack.pop!
+
+      it "signs with ngx.hmac_sha1 without a backend", ->
+        e = require_with_stubs "lapis.util.encoding", {
+          "openssl.hmac": false
+          "resty.openssl.hmac": false
+        }
+
+        assert.same "ngx:sha1:key:msg", e.hmac_sha1 "key", "msg"
+        assert.same { color: "red" }, e.decode_with_secret e.encode_with_secret { color: "red" }
+        assert.has_error -> e.hmac_sha256 "key", "msg"
+
+      it "signs with lua-resty-openssl when hmac_digest is sha256", ->
+        prev_digest = config.hmac_digest
+        config.hmac_digest = "sha256"
+        finally -> config.hmac_digest = prev_digest
+
+        e = require_with_stubs "lapis.util.encoding", {
+          "openssl.hmac": false
+          "resty.openssl.hmac": fake_hmac "resty"
+        }
+
+        assert.same "ngx:sha1:key:msg", e.hmac_sha1 "key", "msg"
+        assert.same "resty:sha256:key:msg", e.hmac_sha256 "key", "msg"
 
+        msg, signature = e.encode_with_secret({ color: "red" })\match "^(.*)%.(.*)$"
+        assert.same "resty:sha256:the-secret:#{msg}", e.decode_base64 signature
diff --git a/spec/helpers.moon b/spec/helpers.moon
index a2df2651..89500054 100644
--- a/spec/helpers.moon
+++ b/spec/helpers.moon
@@ -140,4 +140,33 @@ sorted_pairs = (sort=table.sort) ->
   after_each ->
     _G.pairs = _pairs
 
-{ :with_query_fn, :assert_queries, :stub_queries, :sorted_pairs }
+-- Loads a fresh copy of a module while the modules in stubs are replaced: a
+-- table is returned in their place, and false makes requiring them fail as if
+-- they weren't installed. Everything is put back before returning, so only the
+-- returned copy of the module sees the stubs
+require_with_stubs = (name, stubs) ->
+  prev_loaded = {}
+  prev_preload = {}
+
+  for mod_name, stub in pairs stubs
+    prev_loaded[mod_name] = package.loaded[mod_name]
+    prev_preload[mod_name] = package.preload[mod_name]
+    package.loaded[mod_name] = nil
+    package.preload[mod_name] = if stub
+      -> stub
+    else
+      -> error "module '#{mod_name}' not found (stubbed by spec)", 0
+
+  prev_module = package.loaded[name]
+  package.loaded[name] = nil
+  ok, mod = pcall require, name
+  package.loaded[name] = prev_module
+
+  for mod_name in pairs stubs
+    package.loaded[mod_name] = prev_loaded[mod_name]
+    package.preload[mod_name] = prev_preload[mod_name]
+
+  assert ok, mod
+  mod
+
+{ :with_query_fn, :assert_queries, :stub_queries, :sorted_pairs, :require_with_stubs }