diff --git a/NEWS b/NEWS
index 4b134259..4eb34c6c 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,8 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
 ==========================
 
 4.6.0, unknown release date
+# Secure URI munge hashing algorithm has changed to hash_hmac("sha256", $url, $secret).
+  Please update any verification scripts you may have.
 # URI parsing algorithm was made more strict, so only prefixes which
   looks like schemes will actually be schemes.  Thanks
   Michael Gusev <mgusev@sugarcrm.com> for fixing.
diff --git a/library/HTMLPurifier/ConfigSchema/schema/URI.MungeSecretKey.txt b/library/HTMLPurifier/ConfigSchema/schema/URI.MungeSecretKey.txt
index 0d00f62e..1e17c1d4 100644
--- a/library/HTMLPurifier/ConfigSchema/schema/URI.MungeSecretKey.txt
+++ b/library/HTMLPurifier/ConfigSchema/schema/URI.MungeSecretKey.txt
@@ -11,7 +11,7 @@ DEFAULT: NULL
     to check if a URI has passed through HTML Purifier with this line:
 </p>
 
-<pre>$checksum === sha1($secret_key . ':' . $url)</pre>
+<pre>$checksum === hash_hmac("sha256", $url, $secret_key)</pre>
 
 <p>
     If the output is TRUE, the redirector script should accept the URI.
diff --git a/library/HTMLPurifier/URIFilter/Munge.php b/library/HTMLPurifier/URIFilter/Munge.php
index bab748a7..e9631f2a 100644
--- a/library/HTMLPurifier/URIFilter/Munge.php
+++ b/library/HTMLPurifier/URIFilter/Munge.php
@@ -47,6 +47,9 @@ class HTMLPurifier_URIFilter_Munge extends HTMLPurifier_URIFilter
         $this->parser = new HTMLPurifier_URIParser();
         $this->doEmbed = $config->get('URI.MungeResources');
         $this->secretKey = $config->get('URI.MungeSecretKey');
+        if ($this->secretKey && !function_exists('hash_hmac')) {
+            trigger_error("Cannot use %URI.MungeSecretKey without hash_hmac support.", E_USER_ERROR);
+        }
         return true;
     }
 
@@ -104,7 +107,7 @@ class HTMLPurifier_URIFilter_Munge extends HTMLPurifier_URIFilter
         $this->replace['%p'] = $context->get('CurrentCSSProperty', true);
         // not always available
         if ($this->secretKey) {
-            $this->replace['%t'] = sha1($this->secretKey . ':' . $string);
+            $this->replace['%t'] = hash_hmac("sha256", $string, $this->secretKey);
         }
     }
 }
diff --git a/tests/HTMLPurifier/HTMLT/munge-extra.htmlt b/tests/HTMLPurifier/HTMLT/munge-extra.htmlt
index 4b1c70a9..8438e3cc 100644
--- a/tests/HTMLPurifier/HTMLT/munge-extra.htmlt
+++ b/tests/HTMLPurifier/HTMLT/munge-extra.htmlt
@@ -6,6 +6,6 @@ URI.MungeResources = true
 <a href="http://example.com">Link</a>
 <img src="http://example.com" style="background-image:url(http://example.com);" alt="example.com" />
 --EXPECT--
-<a href="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=&amp;n=a&amp;m=href&amp;p=">Link</a>
-<img src="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=1&amp;n=img&amp;m=src&amp;p=" style="background-image:url(&quot;/redirect?s=http%3A%2F%2Fexample.com&amp;t=c15354f3953dfec262c55b1403067e0d045a3059&amp;r=1&amp;n=img&amp;m=style&amp;p=background-image&quot;);" alt="example.com" />
+<a href="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c763c4a30204eee8470a3292e0f0cd91a639654d039d45f1495a50207847e954&amp;r=&amp;n=a&amp;m=href&amp;p=">Link</a>
+<img src="/redirect?s=http%3A%2F%2Fexample.com&amp;t=c763c4a30204eee8470a3292e0f0cd91a639654d039d45f1495a50207847e954&amp;r=1&amp;n=img&amp;m=src&amp;p=" style="background-image:url(&quot;/redirect?s=http%3A%2F%2Fexample.com&amp;t=c763c4a30204eee8470a3292e0f0cd91a639654d039d45f1495a50207847e954&amp;r=1&amp;n=img&amp;m=style&amp;p=background-image&quot;);" alt="example.com" />
 --# vim: et sw=4 sts=4
diff --git a/tests/HTMLPurifier/HTMLT/secure-munge.htmlt b/tests/HTMLPurifier/HTMLT/secure-munge.htmlt
index 114cb000..bf5b3244 100644
--- a/tests/HTMLPurifier/HTMLT/secure-munge.htmlt
+++ b/tests/HTMLPurifier/HTMLT/secure-munge.htmlt
@@ -5,6 +5,6 @@ URI.MungeSecretKey = "foo"
 <a href="http://localhost">foo</a>
 <img src="http://localhost" alt="local" />
 --EXPECT--
-<a href="/redirect.php?url=http%3A%2F%2Flocalhost&amp;check=8e8223ae8fac24561104180ea549c21fbd111be7">foo</a>
+<a href="/redirect.php?url=http%3A%2F%2Flocalhost&amp;check=c0efad89696082f5cb925d28636b0f4260f346391c92c70c8e9eba72591c2a73">foo</a>
 <img src="http://localhost" alt="local" />
 --# vim: et sw=4 sts=4
diff --git a/tests/HTMLPurifier/URIFilter/MungeTest.php b/tests/HTMLPurifier/URIFilter/MungeTest.php
index 9505a156..60658da2 100644
--- a/tests/HTMLPurifier/URIFilter/MungeTest.php
+++ b/tests/HTMLPurifier/URIFilter/MungeTest.php
@@ -107,7 +107,7 @@ class HTMLPurifier_URIFilter_MungeTest extends HTMLPurifier_URIFilterHarness
     public function testSecureMungeStandard()
     {
         $this->setSecureMunge();
-        $this->assertFiltering('http://google.com', '/redirect.php?url=http%3A%2F%2Fgoogle.com&checksum=0072e2f817fd2844825def74e54443debecf0892');
+        $this->assertFiltering('http://google.com', '/redirect.php?url=http%3A%2F%2Fgoogle.com&checksum=46267a796aca0ea5839f24c4c97ad2648373a4eca31b1c0d1fa7c7ff26798f79');
     }
 
     public function testSecureMungeIgnoreUnknownSchemes()
@@ -127,7 +127,7 @@ class HTMLPurifier_URIFilter_MungeTest extends HTMLPurifier_URIFilterHarness
     {
         $this->setSecureMunge();
         $this->setMunge('/links/%s/%t');
-        $this->assertFiltering('http://google.com', '/links/http%3A%2F%2Fgoogle.com/0072e2f817fd2844825def74e54443debecf0892');
+        $this->assertFiltering('http://google.com', '/links/http%3A%2F%2Fgoogle.com/46267a796aca0ea5839f24c4c97ad2648373a4eca31b1c0d1fa7c7ff26798f79');
     }
 
     public function testMungeIgnoreSameDomain()