From: simon <simon@cda61777-01e9-0310-a592-d414129be87e>
Date: Sat, 15 Mar 2003 18:39:10 +0000 (+0000)
Subject: My comment about RSA blinding was talking slight tosh. Fixed in case
X-Git-Url: https://git.distorted.org.uk/~mdw/sgt/putty/commitdiff_plain/033a3ded0dcac2688eddf18c2b086b2f7d7f7927

My comment about RSA blinding was talking slight tosh. Fixed in case
anyone ever actually reads it :-)


git-svn-id: svn://svn.tartarus.org/sgt/putty@2942 cda61777-01e9-0310-a592-d414129be87e
---

diff --git a/sshrsa.c b/sshrsa.c
index c60823e4..64676660 100644
--- a/sshrsa.c
+++ b/sshrsa.c
@@ -147,15 +147,16 @@ static Bignum rsa_privkey_op(Bignum input, struct RSAKey *key)
     /*
      * RSA blinding relies on the fact that (xy)^d mod n is equal
      * to (x^d mod n) * (y^d mod n) mod n. We invent a random pair
-     * y and y^d; then we multiply x by y, raise to the power e mod
-     * n as usual, and divide by y^d to recover x^d. Thus the
-     * timing of the modpow does not reveal information about x,
-     * but only about xy, which is unpredictable to an attacker.
+     * y and y^d; then we multiply x by y, raise to the power d mod
+     * n as usual, and divide by y^d to recover x^d. Thus an
+     * attacker can't correlate the timing of the modpow with the
+     * input, because they don't know anything about the number
+     * that was input to the actual modpow.
      * 
      * The clever bit is that we don't have to do a huge modpow to
      * get y and y^d; we will use the number we just invented as
-     * _y^d_, and use the RSA public exponent to compute y from it,
-     * which is much faster.
+     * _y^d_, and use the _public_ exponent to compute (y^d)^e = y
+     * from it, which is much faster to do.
      */
     random_encrypted = modpow(random, key->exponent, key->modulus);
     random_inverse = modinv(random, key->modulus);