[
https://issues.apache.org/jira/browse/FTPSERVER-485?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16446066#comment-16446066
]
Jonathan Valliere commented on FTPSERVER-485:
---------------------------------------------
Haven't tested this yet. The following should cost the same amount of cycles
linear to the input length.
{code:java}
public class PasswordUtil {
public static boolean compare(String input, String target) {
/*
* set the default result based on the string lengths; if the
lengths do not
* match then we know that this comparison should always fail.
*/
int result = (input.length() == target.length()) ? 0 : 1;
/*
* cycle through all the input characters regardless of target
length while trying
* to consume the same number of cycles while evaluating the
conditionals.
*/
for (int i = 0; i < input.length(); i++) {
boolean check = (i < target.length());
result |= (input.charAt(i) == target.charAt(check ? i :
0)) ? check ? 0 : 1 : 1;
}
return (result == 0);
}
}
{code}
> Timing Side Channel PasswordEncryptor
> -------------------------------------
>
> Key: FTPSERVER-485
> URL: https://issues.apache.org/jira/browse/FTPSERVER-485
> Project: FtpServer
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.1.1
> Environment: tested on macOS High Sierra 10.13.4, but it is not
> relevant
> Reporter: Yannic Noller
> Assignee: Jonathan Valliere
> Priority: Major
> Labels: easyfix, pull-request-available
> Fix For: 1.1.2
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> Dear Apache FTPServer developers,
> We have found a timing side-channel in class
> org.apache.ftpserver.usermanager.ClearTextPasswordEncryptor, method "public
> boolean matches(String passwordToCheck, String storedPassword)". This is due
> to the use of String.equals for comparison which returns as soon as a
> character does not match. This represents a timing side channel, which could
> be used by a potential attacker to obtain knowledge about the hidden secret
> password.
> Do you agree with our findings?
> A similar issue is present in method "matches" from classes
> org.apache.ftpserver.usermanager.Md5PasswordEncryptor and
> org.apache.ftpserver.usermanager.SaltedPasswordEncryptor.
> We found these classes in the latest version of your git repo:
> https://git-wip-us.apache.org/repos/asf?p=mina-ftpserver.git;a=summary
> The problem can be fixed easily by using the following safe version for
> String comparison in all three methods:
> public boolean isEqual_safe(String a, String b) {
> char a_value[] = a.toCharArray();
> char b_value[] = b.toCharArray();
> boolean unused;
> boolean matches = true;
> for (int i = 0; i < a_value.length; i++) {
> if (i < b_value.length) {
> if (a_value[i] != b_value[i]) {
> matches = false;
> } else {
> unused = true;
> }
> } else {
> unused = false;
> unused = true;
> }
> }
> return matches;
> }
> Do you agree with our patch proposal?
> Please feel free to contact us for further clarification! You can reach us by
> the following email address:
> [email protected]
> Best regards,
> Yannic Noller
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
