Schnorr Ring Signatures - wrong hash results I don't know if I've placed the question right, It is half maths, half programming.
I'm writing Schnorr Ring Signatures on Elliptic Curves in Java and I have a problem. I've found scheme on integers and translated it to elliptic curves.

In point 3 on page 11

$R_s = g^a \prod_{i \neq s}(y_i^{-H(m, R_i)}) \ mod \ p$

and in my elliptic curve version

$R_s = aG + \sum_{i\neq s}(Y_i*-H(m,R_i))$

where $G$ is a generator, $Y_i$ is a public key of i-th user, $m$ is a message and $R_i$ is $a_iG$ where $a_i$ is random.

I have


basepoint $G$
cofactor $h$ to the order of $G$
order $n$ of $G$
points $A$ and $B$


My question is how to perform a modular inverse of $H(m,R_i)$. In Java I have a modInverse method on BigIntegers but I have to know value of $p$. How to find value of $p$? Or how to calculate $-H(m,R_i)$?

EDIT:
OK, thakns. I've found $p$ value. But still I'm getting wrong results. If someone would be so nice to look at it here is my sample code. Thanks in advance for help
If $g^a$ in the modular version translates to $aG$ or $a*G$ in the elliptic curve version, then $y_i^{-H(m, R_i)}$ should translate to
$$\begin{align*}
(-H(m, R_i))*Y_i&amp;=-(H(m, R_i)*Y_i)&amp;\text{(1)}&amp;\text{ or equivalently}\\
&amp;=H(m, R_i)*(-Y_i)&amp;\text{(2)}&amp;\text{ or equivalently}\\
&amp;=((-H(m, R_i))\bmod n)*Y_i&amp;\text{(3)}&amp;\\
\end{align*}$$

The form (1) leads to an expression requiring one point subtraction or inversion:
$$R_s=a*G-\sum_{i\neq s}(H(m,R_i)*Y_i)$$

The form (3) leads to an expression that requires none:
$$R_s=a*G+\sum_{i\neq s}(((-H(m,R_i))\bmod n)*Y_i)$$

Note: By definition, $u\bmod n$ is the uniquely defined $v$ with $0\le v&lt;n$ and $u-v$ a multiple of $n$. When $u\ge0$, $(-u)\bmod n$ can be computed as $n-1-r$, where $r$ is the remainder of the division of $(n-1+u)$ by $n$.