BN_kronecker
if ((jacobi_symbol = BN_kronecker(D, n, ctx)) == -2)
r = BN_kronecker(y, q, ctx); /* here 'q' is |p| */
kron = BN_kronecker(x, &group->field, ctx);
int BN_kronecker(const BIGNUM *a,const BIGNUM *b,BN_CTX *ctx); /* returns -2 for error */