9001039?: DHKeyAgreement calculates wrong TlsPremasterSecret 1 out of 256 times

Thu May 16 07:56:51 UTC 2013

Hi Pasi,

Thank you for your patience, and contribution to OpenJDK.  The bug is
accepted, and you should be able to review it at:

   http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8014618

Let's use the above bug ID to track the issue.

Your patch looks fine in general (I may have some very minor comments
later).  We also have similar problems in PKCS11 provider because of the
update of P11KeyAgreement.java in changeset:

    http://hg.openjdk.java.net/jdk7u/jdk7u-gate/jdk/rev/e574e475c8a6

Would you like to also fix it in your patch?

Thanks again for your nice work.

Regards,
Xuelei

On 5/10/2013 5:00 PM, Pasi Eronen wrote:
> AKA "1 out of 256 SSL/TLS handshakes fails with DHE cipher suites"
> 
> I reported this bug over a month of ago, but for some reason, it's not 
> yet visible at bugs.sun.com <http://bugs.sun.com>. I've included the bug
> report below just in 
> case. 
> 
> It seems this commit from March 2012 inadvertently broke SSL/TLS DHE 
> cipher suites, causing the SSL/TLS handshake to fail approximately 
> 1 out of 256 times: 
> 
> http://hg.openjdk.java.net/jdk7u/jdk7u-gate/jdk/rev/e574e475c8a6
> 
> The commit was done to fix this bug:
> 
> http://bugs.sun.com/view_bug.do?bug_id=7146728
> 
> While generating a secret of the same length as modulus may be the right 
> choice generally speaking (and it's what e.g. IPsec uses), SSL/TLS uses 
> a different convention: leading zeroes must be stripped. 
> 
> This is currently blocking us from updating our production systems to 
> Java 7, so although I have not contributed to OpenJDK before, I'd like 
> to submit a patch and a test case for this (I've signed the OCA 
> already). But before I do this, I'd like to check that the approach is 
> agreeable. 
> 
> We have a separate "algorithm" value "TlsPremasterSecret", so 
> behavior for other cases could stay the same. Would a patch
> like this:
> 
>     } else if (algorithm.equals("TlsPremasterSecret")) {
>         // remove leading zero bytes per RFC 5246 Section 8.1.2
>         int i = 0;
>         while ((i < secret.length - 1) && (secret[i] == 0)) {
>             i++;
>         }
>         if (i == 0) {
>             return new SecretKeySpec(secret, "TlsPremasterSecret");
>         } else {
>             byte[] secret2 = new byte[secret.length - i];
>             System.arraycopy(secret, i, secret2, 0, secret2.length);
>             return new SecretKeySpec(secret2, "TlsPremasterSecret");
>         }
>     }
> 
> Plus a test case (with fixed keys) that checks that leading zero is
> stripped 
> for TlsPremasterSecret and is not stripped otherwise, be sufficient?
> 
> Best regards,
> Pasi
> 
> ---snip---
> 
> Synopsis:
> DHKeyAgreement calculates wrong TlsPremasterSecret 1 out of 256 times
> 
> Full OS version:
> Tested on Windows 7 (Microsoft Windows [Version 6.1.7601]), but occurs in
> e..g OpenJDK 7 as well.
> 
> Development Kit or Runtime version:
> java version "1.7.0_17"
> Java(TM) SE Runtime Environment (build 1.7.0_17-b02)
> Java HotSpot(TM) Client VM (build 23.7-b01, mixed mode, sharing)
> 
> Description:
> When performing Diffie-Hellman key agreement for SSL/TLS, the TLS
> specification (RFC 5246) says that "Leading bytes of Z that contain all zero
> bits are stripped before it is used as the pre_master_secret."
> 
> However, com.sun.crypto.provider.DHKeyAgreement.java does not strip leading
> zero bytes. This causes approximately 1 out 256 SSL/TLS handshakes with
> DH/DHE cipher suites to fail (when the leading byte happens, by chance, to
> be zero).
> 
> Steps to Reproduce:
> 1. Start a simple JSSE socket server with -Djavax.net.debug=all.
> 
> 2. Connect to the server with e.g. OpenSSL command line tool, ensuring that
> DHE cipher suite gets selected (e.g. "openssl s_client -cipher
> DHE-RSA-AES128-SHA -connect 192.168.81.1:9999
> <http://192.168.81.1:9999>") repeatedly. Other SSL
> clients can be used -- this is not an OpenSSL bug (see below).
> 
> 3. Repeat the connection. After a couple of hundred successful connections,
> the connection will fail with handshake_failure alert.
> 
> 4. Examine the JSSE debug logs produced by the server: the failed connection
> will have a PreMaster secret that begins with zero byte
> (while all other connections have non-zero byte here). For example:
> 
> SESSION KEYGEN:
> PreMaster Secret:
> 0000: 00 70 C5 7E 91 38 C8 DE   ED 75 3D 76 8A B5 44 69  .p...8...u=v..Di
> 0010: E7 32 1C EE 80 77 50 C7   A9 51 24 2E E3 15 11 30  .2...wP..Q$....0
> 0020: 9D F6 9F BC 9D EB 5C 18   F7 A4 19 ED 1A AC 2E 0C  ......\.........
> 0030: E3 18 C5 11 B1 80 07 7D   B1 C6 70 A8 D7 EB CF DD  ..........p.....
> 0040: 2D B5 1D BC 01 3E 28 2A   2B 5B 38 8F EB 20 F2 A2  -....>(*+[8.. ..
> 0050: 00 07 47 F7 87 B8 99 CB   EF B4 13 04 C8 8B 82 FB  ..G.............
> 
> Expected Result:
> Expected result is that every connection succeed.
> 
> Actual Result:
> Roughly one out of 256 connections fail.
> 
> Source code for an executable test case:
> 
> Java server:
> 
> import javax.net.ssl.SSLServerSocket;
> import javax.net.ssl.SSLServerSocketFactory;
> import javax.net.ssl.SSLSocket;
> 
> public class TestServer {
>     public static void main(String args[]) throws Exception {
>         SSLServerSocketFactory ssf = (SSLServerSocketFactory)
> SSLServerSocketFactory.getDefault();
>         SSLServerSocket ss = (SSLServerSocket) ssf.createServerSocket(9999);
>         System.out.println("Listening on port 9999");
>         for (String cs : ss.getEnabledCipherSuites()) {
>             System.out.println(cs);
>         }
>         while (true) {
>             SSLSocket s = (SSLSocket) ss.accept();
>             System.out.println("Connected with
> "+s.getSession().getCipherSuite());
>             s.close();
>         }
>     }
> }
> 
> Run as as follows:
> 
> keytool -storepass "password" -keypass "password" -genkey -keyalg RSA
> -keystore test_keystore.jks -dname CN=test
> javac TestServer.java
> java -Djavax.net.debug=all -Djavax.net.ssl.keyStore=./test_keystore.jks
> -Djavax.net.ssl.keyStorePassword=password TestServer
> 
> OpenSSL client:
> 
> set -e
> while true; do
>   openssl s_client -cipher DHE-RSA-AES128-SHA -connect 127.0.0.1:9999
> <http://127.0.0.1:9999> -quiet -no_ign_eof < /dev/null
> done
> 
> Workaround:
> Disable Diffie-Hellman cipher suites.
> 
> ---snip---
> 