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The U.S. Department of Energy
Computer Incident Advisory Capability
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/ | /_\ /
\___ __|__ / \ \___
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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
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PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins. If you are not part of these
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