### Fix comment on the ecc_add_ehh formulas.

parent f8870f78
 ... @@ -55,25 +55,25 @@ ecc_add_ehh (const struct ecc_curve *ecc, ... @@ -55,25 +55,25 @@ ecc_add_ehh (const struct ecc_curve *ecc, #define z3 (r + 2*ecc->p.size) #define z3 (r + 2*ecc->p.size) /* Formulas (from djb, /* 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 Computation Operation Live variables C = x1*x2 mul C C = x1*x2 mul C D = y1*y2 mul C, D 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) E = b*C*D 2 mul C, E, T (Replace C <-- D - C) A = z1*z2 mul A, C, E, T A = z1*z2 mul A, C, E, T B = A^2 sqr A, B, C, E, T B = A^2 sqr A, B, C, E, T F = B - E A, B, C, E, F, T F = B - E A, B, C, E, F, T G = B + E A, C, F, G, 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 y3 = A*G*(D-C) 2 mul F, G z3 = F*G mul z3 = F*G mul But when working with the twist curve, we need to the factor But when working with the twist curve, we have to negate the x1*x2. We need to switch sign in y3 expressions, and swap F and factor C = x1*x2. We change subtract to add in the y3 G. expression, and swap F and G. */ */ #define C scratch #define C scratch #define D (scratch + ecc->p.size) #define D (scratch + ecc->p.size) ... ...
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