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author | Niels Möller <nisse@lysator.liu.se> | 2015-01-27 13:23:21 +0100 |
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committer | Niels Möller <nisse@lysator.liu.se> | 2015-01-27 13:23:21 +0100 |
commit | 2d4b582e0164fc7fa9e130c6ff4c96b8924fcdd8 (patch) | |
tree | 1c4127a35c8b04742f743ea755f75a98b903a9bf /ecc-add-ehh.c | |
parent | f8870f786aa9fb5f69921e7243d660932ffec061 (diff) | |
download | nettle-2d4b582e0164fc7fa9e130c6ff4c96b8924fcdd8.tar.gz |
Fix comment on the ecc_add_ehh formulas.
Diffstat (limited to 'ecc-add-ehh.c')
-rw-r--r-- | ecc-add-ehh.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/ecc-add-ehh.c b/ecc-add-ehh.c index e8155bef..8fdc9ec3 100644 --- a/ecc-add-ehh.c +++ b/ecc-add-ehh.c @@ -55,25 +55,25 @@ ecc_add_ehh (const struct ecc_curve *ecc, #define z3 (r + 2*ecc->p.size) /* Formulas (from djb, - http://www.hyperelliptic.org/EFD/g1p/auto-edwards-projective.html#doubling-dbl-2007-bl): + http://www.hyperelliptic.org/EFD/g1p/auto-edwards-projective.html#addition-add-2007-bl): Computation Operation Live variables C = x1*x2 mul C D = y1*y2 mul C, D - T = (x1+y1)(x2+y2) - C - D C, D, T + T = (x1+y1)(x2+y2) - C - D, mul C, D, T E = b*C*D 2 mul C, E, T (Replace C <-- D - C) A = z1*z2 mul A, C, E, T B = A^2 sqr A, B, C, E, T F = B - E A, B, C, E, F, T G = B + E A, C, F, G, T - x3 = A*F*T 3 mul A, C, G + x3 = A*F*T 2 mul A, C, G y3 = A*G*(D-C) 2 mul F, G z3 = F*G mul - But when working with the twist curve, we need to the factor - x1*x2. We need to switch sign in y3 expressions, and swap F and - G. + But when working with the twist curve, we have to negate the + factor C = x1*x2. We change subtract to add in the y3 + expression, and swap F and G. */ #define C scratch #define D (scratch + ecc->p.size) |