int ecc_octet2point ( point_t *P, uint8_t *octet, uint16_t octet_len )
{
NN_DIGIT alpha[NUMWORDS], tmp[NUMWORDS];
if ( octet[0] == 0 ) { //infinity
NN_AssignZero ( P->x, NUMWORDS );
NN_AssignZero ( P->y, NUMWORDS );
} else if ( octet[0] == 4 ) { //non compressed
NN_Decode ( P->x, NUMWORDS, octet+1, KEYDIGITS*NN_DIGIT_LEN );
NN_Decode ( P->y, NUMWORDS, octet+1+KEYDIGITS*NN_DIGIT_LEN, KEYDIGITS*NN_DIGIT_LEN );
return 2*KEYDIGITS*NN_DIGIT_LEN+1;
} else if ( octet[0] == 2 || octet[0] == 3 ) { //compressed form
NN_Decode ( P->x, NUMWORDS, octet+1, KEYDIGITS*NN_DIGIT_LEN );
//compute y
NN_ModSqrOpt ( alpha, P->x, param.p, param.omega, NUMWORDS );
NN_ModMultOpt ( alpha, alpha, P->x, param.p, param.omega, NUMWORDS );
NN_ModMultOpt ( tmp, param.E.a, P->x, param.p, param.omega, NUMWORDS );
NN_ModAdd ( tmp, tmp, alpha, param.p, NUMWORDS );
NN_ModAdd ( tmp, tmp, param.E.b, param.p, NUMWORDS );
NN_ModSqrOpt ( P->y, tmp, param.p, NUMWORDS, param.omega );
if ( octet[0] == 3 ) {
NN_ModSub ( P->y, param.p, P->y, param.p, NUMWORDS );
}
return KEYDIGITS*NN_DIGIT_LEN+1;
}
return -1;
}
/* Generates a probable prime a between b and c such that a-1 is divisible by d.
Lengths: a[digits], b[digits], c[digits], d[digits].
Assumes b < c, digits < MAX_NN_DIGITS.
Returns RE_NEED_RANDOM if randomStruct not seeded, RE_DATA if
unsuccessful.
*/
int GeneratePrime(NN_DIGIT *a, NN_DIGIT *b, NN_DIGIT *c, NN_DIGIT *d, unsigned int digits, R_RANDOM_STRUCT *randomStruct)
{
int status;
unsigned char block[MAX_NN_DIGITS * NN_DIGIT_LEN];
NN_DIGIT t[MAX_NN_DIGITS], u[MAX_NN_DIGITS];
/* Generate random number between b and c.
*/
if ((status = R_GenerateBytes (block, digits * NN_DIGIT_LEN, randomStruct))!=0) return (status);
NN_Decode (a, digits, block, digits * NN_DIGIT_LEN);
NN_Sub (t, c, b, digits);
NN_ASSIGN_DIGIT (u, 1, digits);
NN_Add (t, t, u, digits);
NN_Mod (a, a, digits, t, digits);
NN_Add (a, a, b, digits);
/* Adjust so that a-1 is divisible by d.
*/
NN_Mod (t, a, digits, d, digits);
NN_Sub (a, a, t, digits);
NN_Add (a, a, u, digits);
if (NN_Cmp (a, b, digits) < 0) NN_Add (a, a, d, digits);
if (NN_Cmp (a, c, digits) > 0) NN_Sub (a, a, d, digits);
/* Search to c in steps of d.
*/
NN_Assign (t, c, digits);
NN_Sub (t, t, d, digits);
while (! ProbablePrime (a, digits)) {
if (NN_Cmp (a, t, digits) > 0) return (RE_DATA);
NN_Add(a, a, d, digits);
};
return (0);
}
