diff --git a/lib/landline/util/cookie.rb b/lib/landline/util/cookie.rb
index 7d9a3d5..70467b4 100644
--- a/lib/landline/util/cookie.rb
+++ b/lib/landline/util/cookie.rb
@@ -3,6 +3,7 @@
 require_relative 'parseutils'
 require_relative 'errors'
 require 'date'
+require 'openssl'
 HeaderRegexp = Landline::Util::HeaderRegexp
 ParserCommon = Landline::Util::ParserCommon
 
@@ -29,15 +30,22 @@ module Landline
         raise Landline::ParsingError, "invalid cookie value: #{value}"
       end
 
+      # Make param keys strings
+      params.transform_keys!(&:to_s)
+
       # Primary cookie parameters
       @key = key
       @value = value
       setup_params(params)
+
+      # Cookie signing parameters
+      setup_hmac(params)
     end
 
     # Convert cookie to "Set-Cookie: " string representation.
     # @return [String]
     def to_s
+      sign(@hmac, algorithm: @algorithm, sep: @sep) if @hmac
       ParserCommon.make_value(
         "#{key.to_s.strip}=#{value.to_s.strip}",
         {
@@ -58,6 +66,26 @@ module Landline
       "#{key.to_s.strip}=#{value.to_s.strip}"
     end
 
+    # Sign the cookie value with HMAC
+    # @param key [String] HMAC signing key
+    # @param algorithm [String] Hash algorithm to use
+    # @param sep [String] Hash separator
+    def sign(key, algorithm: "sha256", sep: "&")
+      @value += sep + ::OpenSSL::HMAC.base64digest(algorithm, key, @value)
+    end
+
+    # Verify HMAC signature
+    # @param key [String] HMAC signing key
+    # @param algorithm [String] Hash algorithm
+    # @param sep [String] Hash separator
+    # @return [Boolean] whether value is signed and valid
+    def verify(key, algorithm: "sha256", sep: "&")
+      val, sig = @value.match(/\A(.*)#{sep}([A-Za-z0-9+\/=]+)\Z/).to_a[1..]
+      return false unless val and sig
+
+      sig == ::OpenSSL::HMAC.base64digest(algorithm, key, val)
+    end
+
     attr_accessor :key, :value
     attr_reader :domain, :path, :expires, :maxage, :samesite, :secure, :httponly
 
@@ -66,7 +94,7 @@ module Landline
     # @return [Cookie]
     def self.from_setcookie_string(data)
       kvpair, params = parse_value(data, regexp: HeaderRegexp::COOKIE_PARAM)
-      key, value = kvpair.split("=").map(&:strip)
+      key, value = kvpair.match(/([^=]+)=?(.*)/).to_a[1..].map(&:strip)
       Cookie.new(key, value, params)
     end
 
@@ -76,7 +104,8 @@ module Landline
     def self.from_cookie_string(data)
       hash = {}
       data.split(";").map do |cookiestr|
-        cookie = Cookie.new(*cookiestr.split("=").map(&:strip))
+        key, value = cookiestr.match(/([^=]+)=?(.*)/).to_a[1..].map(&:strip)
+        cookie = Cookie.new(key, value)
         if hash[cookie.key]
           hash[cookie.key].append(cookie)
         else
@@ -88,6 +117,12 @@ module Landline
 
     private
 
+    def setup_hmac(params)
+      @hmac = params['hmac']
+      @algorithm = (params['algorithm'] or "sha256")
+      @sep = (params['sep'] or "&")
+    end
+
     def setup_params(params)
       # Extended cookie params
       params.transform_keys!(&:downcase)