add pow_mod for DHM-Exchange

rust/server/src/main.rs

@@ -4,6 +4,8 @@ use serde::{Serialize, Deserialize};
 use sha2::{Digest,Sha512};
 use regex::Regex;
 use crc32fast;
+use rand::{rngs::StdRng, RngCore, SeedableRng};
+use num_bigint::BigUint;
 
 mod big_array;
 use big_array::BigArray;
@@ -36,6 +38,18 @@ struct StrPacket {
     payload: [u8; MAX_PAYLOAD_U]
 }
 
+fn pow_mod(num: BigUint, pow: BigUint, modulo: BigUint) -> BigUint {
+    let mut result = BigUint::from(1u8);
+    let one = BigUint::from(1u8);
+    let mut i = BigUint::from(0u8);
+    while i < pow {
+        result = (result * &num) % &modulo;
+        i += &one;
+    }
+
+    result
+}
+
 fn main() {
     let port = "1337";
     let timeout = 100; //ms