changeset 16520:02bb07ba5b81

8168728: DSA signing improvments Reviewed-by: valeriep, vinnie, ahgross, asmotrak, robm
author xuelei
date Thu, 10 Nov 2016 15:46:40 +0000
parents 874d9919be26
children b9bb059565a3
files src/java.base/share/classes/sun/security/provider/DSA.java
diffstat 1 files changed, 38 insertions(+), 2 deletions(-) [+]
line wrap: on
line diff
--- a/src/java.base/share/classes/sun/security/provider/DSA.java	Wed Oct 12 12:56:35 2016 -0400
+++ b/src/java.base/share/classes/sun/security/provider/DSA.java	Thu Nov 10 15:46:40 2016 +0000
@@ -427,13 +427,49 @@
         return t5.mod(q);
     }
 
-    // NOTE: This following impl is defined in FIPS 186-4 AppendixB.2.1.
     protected BigInteger generateK(BigInteger q) {
+        // Implementation defined in FIPS 186-4 AppendixB.2.1.
         SecureRandom random = getSigningRandom();
         byte[] kValue = new byte[(q.bitLength() + 7)/8 + 8];
 
         random.nextBytes(kValue);
-        return new BigInteger(1, kValue).mod(q.subtract(BigInteger.ONE)).add(BigInteger.ONE);
+        BigInteger k = new BigInteger(1, kValue).mod(
+                q.subtract(BigInteger.ONE)).add(BigInteger.ONE);
+
+        // Using an equivalent exponent of fixed length (same as q or 1 bit
+        // less than q) to keep the kG timing relatively constant.
+        //
+        // Note that this is an extra step on top of the approach defined in
+        // FIPS 186-4 AppendixB.2.1 so as to make a fixed length K.
+        k = k.add(q).divide(BigInteger.TWO);
+
+        // An alternative implementation based on FIPS 186-4 AppendixB2.2
+        // with fixed-length K.
+        //
+        // Please keep it here as we may need to switch to it in the future.
+        //
+        // SecureRandom random = getSigningRandom();
+        // byte[] kValue = new byte[(q.bitLength() + 7)/8];
+        // BigInteger d = q.subtract(BigInteger.TWO);
+        // BigInteger k;
+        // do {
+        //     random.nextBytes(kValue);
+        //     BigInteger c = new BigInteger(1, kValue);
+        //     if (c.compareTo(d) <= 0) {
+        //         k = c.add(BigInteger.ONE);
+        //         // Using an equivalent exponent of fixed length to keep
+        //         // the g^k timing relatively constant.
+        //         //
+        //         // Note that this is an extra step on top of the approach
+        //         // defined in FIPS 186-4 AppendixB.2.2 so as to make a
+        //         // fixed length K.
+        //         if (k.bitLength() >= q.bitLength()) {
+        //             break;
+        //         }
+        //     }
+        // } while (true);
+
+        return k;
     }
 
     // Use the application-specified SecureRandom Object if provided.