Visit our newest sister site!
Hundreds of free aircraft flight manuals
Civilian • Historical • Military • Declassified • FREE!


TUCoPS :: Web :: General :: n-061.txt

OpenSSL Timing-based Attacks on RSA Keys (CIAC N-061)




             __________________________________________________________

                       The U.S. Department of Energy
                   Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___
             __________________________________________________________

                             INFORMATION BULLETIN

                    OpenSSL Timing-based Attacks on RSA Keys
                  [OpenSSL Security Advisory [17 March 2003]]

March 20, 2003 14:00 GMT                                          Number N-061
[REVISED May 20, 2003]
______________________________________________________________________________
PROBLEM:       A timing-based attack on RSA keys vulnerability has been 
               identified in OpenSSL v0.9.7a and 0.9.6i unless RSA blinding 
               has been turned on. 
AFFECTED 
SOFTWARE:      OpenSSL v0.9.7a and 0.9.6i 
DAMAGE:        Local or remote attackers could obtain the server's private 
               key by determining factors using timing differences. 
SOLUTION:      Apply available patch or upgrade OpenSSL. 
______________________________________________________________________________
VULNERABILITY  The risk is MEDIUM. This problem affects many applications 
ASSESSMENT:    using OpenSSL, in particular, almost all SSL-enabled Apaches. 
               OpenSSL does not use RSA blinding by default. 
______________________________________________________________________________
LINKS: 
 CIAC BULLETIN:      http://www.ciac.org/ciac/bulletins/n-061.shtml 
 ORIGINAL BULLETIN:  http://www.openssl.org/news/secadv_20030317.txt
 ADDITIONAL          SGI Security Advisory 20030501-01-I for IRIX 6.5.19, 6.5.20
 INFORMATION:        ftp://patches.sgi.com/support/free/security/advisories
                        /20030501-01-I
______________________________________________________________________________

Revision History:
5/20/03 - Added link to SGI Security Advisory 20030501-01-I

[***** Start OpenSSL Security Advisory [17 March 2003] *****]


OpenSSL Security Advisory [17 March 2003]

Timing-based attacks on RSA keys
================================

OpenSSL v0.9.7a and 0.9.6i vulnerability
----------------------------------------

Researchers have discovered a timing attack on RSA keys, to which
OpenSSL is generally vulnerable, unless RSA blinding has been turned
on.

Typically, it will not have been, because it is not easily possible to
do so when using OpenSSL to provide SSL or TLS.

The enclosed patch switches blinding on by default. Applications that
wish to can remove the blinding with RSA_blinding_off(), but this is
not generally advised. It is also possible to disable it completely by
defining OPENSSL_NO_FORCE_RSA_BLINDING at compile-time.

The performance impact of blinding appears to be small (a few
percent).

This problem affects many applications using OpenSSL, in particular,
almost all SSL-enabled Apaches. You should rebuild and reinstall
OpenSSL, and all affected applications.

The Common Vulnerabilities and Exposures project (cve.mitre.org) has
assigned the name CAN-2003-0147 to this issue.

We strongly advise upgrading OpenSSL in all cases, as a precaution.

Index: crypto/rsa/rsa_eay.c
===================================================================
RCS file: /e/openssl/cvs/openssl/crypto/rsa/rsa_eay.c,v
retrieving revision 1.28.2.3
diff -u -r1.28.2.3 rsa_eay.c
--- crypto/rsa/rsa_eay.c	30 Jan 2003 17:37:46 -0000	1.28.2.3
+++ crypto/rsa/rsa_eay.c	16 Mar 2003 10:34:13 -0000
@@ -195,6 +195,25 @@
 	return(r);
 	}
 
+static int rsa_eay_blinding(RSA *rsa, BN_CTX *ctx)
+	{
+	int ret = 1;
+	CRYPTO_w_lock(CRYPTO_LOCK_RSA);
+	/* Check again inside the lock - the macro's check is racey */
+	if(rsa->blinding == NULL)
+		ret = RSA_blinding_on(rsa, ctx);
+	CRYPTO_w_unlock(CRYPTO_LOCK_RSA);
+	return ret;
+	}
+
+#define BLINDING_HELPER(rsa, ctx, err_instr) \
+	do { \
+		if(((rsa)->flags & RSA_FLAG_BLINDING) && \
+				((rsa)->blinding == NULL) && \
+				!rsa_eay_blinding(rsa, ctx)) \
+			err_instr \
+	} while(0)
+
 /* signing */
 static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 	     unsigned char *to, RSA *rsa, int padding)
@@ -239,8 +258,8 @@
 		goto err;
 		}
 
-	if ((rsa->flags & RSA_FLAG_BLINDING) && (rsa->blinding == NULL))
-		RSA_blinding_on(rsa,ctx);
+	BLINDING_HELPER(rsa, ctx, goto err;);
+
 	if (rsa->flags & RSA_FLAG_BLINDING)
 		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
 
@@ -318,8 +337,8 @@
 		goto err;
 		}
 
-	if ((rsa->flags & RSA_FLAG_BLINDING) && (rsa->blinding == NULL))
-		RSA_blinding_on(rsa,ctx);
+	BLINDING_HELPER(rsa, ctx, goto err;);
+
 	if (rsa->flags & RSA_FLAG_BLINDING)
 		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
 
Index: crypto/rsa/rsa_lib.c
===================================================================
RCS file: /e/openssl/cvs/openssl/crypto/rsa/rsa_lib.c,v
retrieving revision 1.30.2.2
diff -u -r1.30.2.2 rsa_lib.c
--- crypto/rsa/rsa_lib.c	30 Jan 2003 17:37:46 -0000	1.30.2.2
+++ crypto/rsa/rsa_lib.c	16 Mar 2003 10:34:13 -0000
@@ -72,7 +72,13 @@
 
 RSA *RSA_new(void)
 	{
-	return(RSA_new_method(NULL));
+	RSA *r=RSA_new_method(NULL);
+
+#ifndef OPENSSL_NO_FORCE_RSA_BLINDING
+	r->flags|=RSA_FLAG_BLINDING;
+#endif
+
+	return r;
 	}
 
 void RSA_set_default_method(const RSA_METHOD *meth)



[***** End OpenSSL Security Advisory [17 March 2003] *****]
_______________________________________________________________________________

CIAC wishes to acknowledge the contributions of OpenSSL for the 
information contained in this bulletin.
_______________________________________________________________________________


CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
    Voice:    +1 925-422-8193 (7x24)
    FAX:      +1 925-423-8002
    STU-III:  +1 925-423-2604
    E-mail:   ciac@ciac.org

Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.

   World Wide Web:      http://www.ciac.org/
   Anonymous FTP:       ftp.ciac.org

PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins.  If you are not part of these
communities, please contact your agency's response team to report
incidents. Your agency's team will coordinate with CIAC. The Forum of
Incident Response and Security Teams (FIRST) is a world-wide
organization. A list of FIRST member organizations and their
constituencies can be obtained via WWW at http://www.first.org/.

This document was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial products,
process, or service by trade name, trademark, manufacturer, or
otherwise, does not necessarily constitute or imply its endorsement,
recommendation or favoring by the United States Government or the
University of California. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States
Government or the University of California, and shall not be used for
advertising or product endorsement purposes.

LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)

N-051: Red Hat Updated OpenSSL Packages Fix Timing Attack
N-052: PeopleSoft PeopleTools Remote Command Execution Vulnerability
N-053: Increased Activity Targeting Microsoft Windows Shares
N-054: Unchecked Buffer in Windows Component Could Cause Web Server Compromise
N-055: Samba smbd Buffer Overrun Vulnerability
N-056: Red Hat Updated 2.4 Kernel Fix for ptrace Vulnerability
N-057: Cryptographic weaknesses in Kerberos v4 protocol
N-058: Vulnerabilities in Webmin/Usermin
N-059: Integer overflow in Sun RPC XDR library routines
N-060: Vulnerabilities in Tomcat 3.3.1





TUCoPS is optimized to look best in Firefox® on a widescreen monitor (1440x900 or better).
Site design & layout copyright © 1986-2014 AOH