diff --git a/java/org/apache/catalina/realm/MessageDigestCredentialHandler.java b/java/org/apache/catalina/realm/MessageDigestCredentialHandler.java
index b5ab367b8479..13cc432e2380 100644
--- a/java/org/apache/catalina/realm/MessageDigestCredentialHandler.java
+++ b/java/org/apache/catalina/realm/MessageDigestCredentialHandler.java
@@ -135,7 +135,7 @@ public boolean matches(String inputCredentials, String storedCredentials) {
 
         if (getAlgorithm() == null) {
             // No digests, compare directly
-            return ConstantTime.equals(inputCredentials, storedCredentials, false);
+            return ConstantTime.equals(storedCredentials, inputCredentials, false);
         } else {
             // Some directories and databases prefix the password with the hash
             // type. The string is in a format compatible with Base64.encode not
@@ -148,7 +148,7 @@ public boolean matches(String inputCredentials, String storedCredentials) {
                         inputCredentials.getBytes(StandardCharsets.ISO_8859_1));
                 String base64UserDigest = Base64.getEncoder().encodeToString(userDigest);
 
-                return ConstantTime.equals(base64UserDigest, base64ServerDigest, false);
+                return ConstantTime.equals(base64ServerDigest, base64UserDigest, false);
             } else if (storedCredentials.startsWith("{SSHA}")) {
                 // "{SSHA}<sha-1 digest:20><salt:n>"
                 // Need to convert the salt to bytes to apply it to the user's
@@ -179,7 +179,7 @@ public boolean matches(String inputCredentials, String storedCredentials) {
                 byte[] userDigestBytes = ConcurrentMessageDigest.digest(getAlgorithm(),
                         inputCredentials.getBytes(StandardCharsets.ISO_8859_1), serverSaltBytes);
 
-                return ConstantTime.equals(userDigestBytes, serverDigestBytes);
+                return ConstantTime.equals(serverDigestBytes, userDigestBytes);
             } else if (storedCredentials.indexOf('$') > -1) {
                 return matchesSaltIterationsEncoded(inputCredentials, storedCredentials);
             } else {
diff --git a/java/org/apache/coyote/ajp/AjpProcessor.java b/java/org/apache/coyote/ajp/AjpProcessor.java
index c27c41b285ad..e197eeb0df68 100644
--- a/java/org/apache/coyote/ajp/AjpProcessor.java
+++ b/java/org/apache/coyote/ajp/AjpProcessor.java
@@ -825,7 +825,7 @@ private void prepareRequest() {
                     requestHeaderMessage.getBytes(tmpMB);
                     if (secret != null && !secret.isEmpty()) {
                         secretPresentInRequest = true;
-                        if (!ConstantTime.equals(tmpMB.getByteChunk(), secret)) {
+                        if (!ConstantTime.equals(secret, tmpMB.getByteChunk())) {
                             response.setStatus(403);
                             setErrorState(ErrorState.CLOSE_CLEAN, null);
                         }
diff --git a/java/org/apache/tomcat/util/security/ConstantTime.java b/java/org/apache/tomcat/util/security/ConstantTime.java
index 992cfdf82554..41711fb41d54 100644
--- a/java/org/apache/tomcat/util/security/ConstantTime.java
+++ b/java/org/apache/tomcat/util/security/ConstantTime.java
@@ -121,6 +121,48 @@ public static boolean equals(final ByteChunk bc, final String s) {
         return result == 0;
     }
 
+    /**
+     * Implements String / ByteChunk equality which always compares all characters, without stopping early if any
+     * characters do not match.
+     * <p>
+     * <i>Note:</i> This implementation was adapted from {@link MessageDigest#isEqual} which we assume is as
+     * optimizer-defeating as possible.
+     *
+     * @param s  The string to compare.
+     * @param bc The ByteChunk to compare.
+     *
+     * @return <code>true</code> if the strings are equal to each other, <code>false</code> otherwise.
+     */
+    public static boolean equals(final String s, final ByteChunk bc) {
+        if (s == null && bc == null) {
+            return true;
+        }
+        if (s == null || bc == null) {
+            return false;
+        }
+
+        final int len1 = s.length();
+        final int len2 = bc.getLength();
+
+        byte[] bytes = bc.getBytes();
+
+        if (len2 == 0) {
+            return len1 == 0;
+        }
+
+        int result = 0;
+        result |= len1 - len2;
+
+        // time-constant comparison
+        for (int i = 0; i < len1; i++) {
+            // If i >= len2, index2 is 0; otherwise, i.
+            final int index2 = ((i - len2) >>> 31) * i;
+            char c = s.charAt(i);
+            byte b = bytes[bc.getStart() + index2];
+            result |= c ^ (b & 0xFF);
+        }
+        return result == 0;
+    }
 
     /**
      * Implements byte-array equality which always compares all bytes in the array, without stopping early if any bytes