SEC-1666: Use constant time comparison for sensitive data.

Constant time comparison helps to mitigate timing attacks. See the following link for more information

 * http://rdist.root.org/2010/07/19/exploiting-remote-timing-attacks/
 * http://en.wikipedia.org/wiki/Timing_attack for more information.

core/src/main/java/org/springframework/security/authentication/encoding/LdapShaPasswordEncoder.java

@@ -145,7 +145,7 @@ public class LdapShaPasswordEncoder implements PasswordEncoder {
 
         String encodedRawPass = encodePassword(rawPass, salt).substring(startOfHash);
 
-        return encodedRawPass.equals(encPass.substring(startOfHash));
+        return PasswordEncoderUtils.equals(encodedRawPass,encPass.substring(startOfHash));
     }
 
     /**

core/src/main/java/org/springframework/security/authentication/encoding/Md4PasswordEncoder.java

@@ -78,7 +78,7 @@ public class Md4PasswordEncoder extends BaseDigestPasswordEncoder {
     public boolean isPasswordValid(String encPass, String rawPass, Object salt) {
         String pass1 = "" + encPass;
         String pass2 = encodePassword(rawPass, salt);
-        return pass1.equals(pass2);
+        return PasswordEncoderUtils.equals(pass1,pass2);
     }
 
     public String getAlgorithm() {

core/src/main/java/org/springframework/security/authentication/encoding/MessageDigestPasswordEncoder.java

@@ -126,7 +126,7 @@ public class MessageDigestPasswordEncoder extends BaseDigestPasswordEncoder {
         String pass1 = "" + encPass;
         String pass2 = encodePassword(rawPass, salt);
 
-        return pass1.equals(pass2);
+        return PasswordEncoderUtils.equals(pass1,pass2);
     }
 
     public String getAlgorithm() {

core/src/main/java/org/springframework/security/authentication/encoding/PasswordEncoderUtils.java

@@ -0,0 +1,45 @@
+package org.springframework.security.authentication.encoding;
+
+import java.io.UnsupportedEncodingException;
+
+/**
+ * Utility for constant time comparison to prevent against timing attacks.
+ *
+ * @author Rob Winch
+ */
+class PasswordEncoderUtils {
+
+    /**
+     * Constant time comparison to prevent against timing attacks.
+     * @param expected
+     * @param actual
+     * @return
+     */
+    static boolean equals(String expected, String actual) {
+        byte[] expectedBytes = bytesUtf8(expected);
+        byte[] actualBytes = bytesUtf8(actual);
+        int expectedLength = expectedBytes == null ? -1 : expectedBytes.length;
+        int actualLength = actualBytes == null ? -1 : actualBytes.length;
+        if (expectedLength != actualLength) {
+            return false;
+        }
+
+        int result = 0;
+        for (int i = 0; i < expectedLength; i++) {
+            result |= expectedBytes[i] ^ actualBytes[i];
+        }
+        return result == 0;
+    }
+
+    private static byte[] bytesUtf8(String s) {
+        if(s == null) {
+            return null;
+        }
+        try {
+            return s.getBytes("UTF-8");
+        } catch (UnsupportedEncodingException e) {
+            throw new IllegalStateException("Could not get bytes in UTF-8 format",e);
+        }
+    }
+    private PasswordEncoderUtils() {}
+}

core/src/main/java/org/springframework/security/authentication/encoding/PlaintextPasswordEncoder.java

@@ -15,6 +15,8 @@
 
 package org.springframework.security.authentication.encoding;
 
+import java.util.Locale;
+
 /**
  * <p>Plaintext implementation of PasswordEncoder.</p>
  *  <P>As callers may wish to extract the password and salts separately from the encoded password, the salt must
@@ -46,11 +48,12 @@ public class PlaintextPasswordEncoder extends BasePasswordEncoder {
         // authentication will fail as the encodePassword never allows them)
         String pass2 = mergePasswordAndSalt(rawPass, salt, false);
 
-        if (!ignorePasswordCase) {
-            return pass1.equals(pass2);
-        } else {
-            return pass1.equalsIgnoreCase(pass2);
+        if (ignorePasswordCase) {
+            // Note: per String javadoc to get correct results for Locale insensitive, use English
+            pass1 = pass1.toLowerCase(Locale.ENGLISH);
+            pass2 = pass2.toLowerCase(Locale.ENGLISH);
         }
+        return PasswordEncoderUtils.equals(pass1,pass2);
     }
 
     /**

core/src/test/java/org/springframework/security/authentication/encoding/PasswordEncoderUtilsTests.java

@@ -0,0 +1,33 @@
+package org.springframework.security.authentication.encoding;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+/**
+ * @author Rob Winch
+ */
+public class PasswordEncoderUtilsTests {
+
+    @Test
+    public void differentLength() {
+        assertFalse(PasswordEncoderUtils.equals("abc", "a"));
+        assertFalse(PasswordEncoderUtils.equals("a", "abc"));
+    }
+
+    @Test
+    public void equalsNull() {
+        assertFalse(PasswordEncoderUtils.equals(null, "a"));
+        assertFalse(PasswordEncoderUtils.equals("a", null));
+        assertTrue(PasswordEncoderUtils.equals(null, null));
+    }
+
+    @Test
+    public void equalsCaseSensitive() {
+        assertFalse(PasswordEncoderUtils.equals("aBc", "abc"));
+    }
+
+    @Test
+    public void equalsSuccess() {
+        assertTrue(PasswordEncoderUtils.equals("abcdef", "abcdef"));
+    }
+}