Fix the ctr mode that does not propagate the carry for the counter

bitwiseshiftleft · Feb 20, 2019 · f7a7a34 · f7a7a34
1 parent 2a6ed4a
commit f7a7a34
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Showing 2 changed files with 9 additions and 2 deletions.
diff --git a/core/ctr.js b/core/ctr.js
@@ -64,7 +64,9 @@ sjcl.beware["CTR mode is dangerous because it doesn't protect message integrity.
         d[i+1] ^= e[1];
         d[i+2] ^= e[2];
         d[i+3] ^= e[3];
-        c[3]++;
+        for(var carry = 3; carry >= 0; carry--) {
+          if (++c[carry]) break; // If overflowing, it'll be 0 and we'll have to continue propagating the carry
+        }
       }
       return sjcl.bitArray.clamp(d, bl);
     }

diff --git a/test/ctr_vectors.js b/test/ctr_vectors.js
@@ -88,5 +88,10 @@ sjcl.test.vector.ctr = [
   { key: '3d25c893d44c4a831b5df70dd4796e31da1511fbcc01050ed3136a3546587448',
     iv:  '6d794b58f8f72cc5176fea41d7b8103e',
     pt:  '77f1a3c4e2abe13f46e978d37eef76eca76561cbb8b5ad55a07300b32e6df3fe',
-    ct:  '9b07440ffb0d8136d0adf8b93784bf24fbabc75def9806b33a7d06887204151e'}
+    ct:  '9b07440ffb0d8136d0adf8b93784bf24fbabc75def9806b33a7d06887204151e'},
+  { key: '3d25c893d44c4a831b5df70dd4796e31da1511fbcc01050ed3136a3546587448',
+    iv:  'abcdef90ffffffffffffffffffffffff',
+    pt:  '77f1a3c4e2abe13f46e978d37eef76eca76561cbb8b5ad55a07300b32e6df3fe',
+    ct:  'ff9be0c14b6a5c8fa99fa5142ab65951144aa48854785395d5251fe285c053e7'},
+
 ];