From 7c97a02804135a582b50b588ed134464b7567df6 Mon Sep 17 00:00:00 2001
From: mgostIH <dennizmodesti@gmail.com>
Date: Thu, 2 Jul 2020 11:12:05 +0200
Subject: [PATCH 1/2] Removed bigint dependency and changed RSA algorithm to
 use u128

---
 Cargo.toml |  7 +------
 src/cb7.rs | 38 +++++++++++++++++++++++++++++++-------
 2 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index c0b2305..dcd7b9b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,9 +16,4 @@ edition = "2018"
 name = "codebreaker"
 
 [dependencies]
-bytemuck = "1.2"
-num-bigint = "0.3"
-
-[features]
-default = ["std"]
-std = ["num-bigint/std"]
+bytemuck = "1.2"
\ No newline at end of file
diff --git a/src/cb7.rs b/src/cb7.rs
index 0c4e404..bac3d6f 100644
--- a/src/cb7.rs
+++ b/src/cb7.rs
@@ -303,16 +303,40 @@ const fn mod_inverse(x: u32) -> u32 {
 
 // RSA encryption/decryption
 fn rsa_crypt(addr: &mut u32, val: &mut u32, rsakey: u64, modulus: u64) {
-    use num_bigint::BigUint;
+    // Code directly copy pasted from Rust's std, with addition of % modulus
+    pub fn mod_pow(base : u64, exp: u64, modulus : u64) -> u64 {
+        let mut base = base as u128;
+        let mut exp = exp as u128;
+        let modulus = modulus as u128;
+        let mut acc = 1;
+
+        while exp > 1 {
+            if (exp & 1) == 1 {
+                acc = acc * base;
+                acc %= modulus;
+            }
+            exp /= 2;
+            base = base * base;
+            base %= modulus;
+        }
 
-    let code = BigUint::from_slice(&[*val, *addr]);
-    let m = BigUint::from(modulus);
+        // Deal with the final bit of the exponent separately, since
+        // squaring the base afterwards is not necessary and may cause a
+        // needless overflow.
+        if exp == 1 {
+            acc = acc * base;
+        }
+
+        (acc % modulus) as u64
+    }
+    
+    let code = (*addr as u64) << 32 | (*val as u64);
 
     // Exponentiation is only invertible if code < modulus
-    if code < m {
-        let digits = code.modpow(&BigUint::from(rsakey), &m).to_u32_digits();
-        *addr = digits[1];
-        *val = digits[0];
+    if code < modulus {
+        let digits = mod_pow(code, rsakey, modulus);
+        *addr = (digits >> 32) as u32;
+        *val = digits as u32;
     }
 }
 

From b8fd3fb02a9d3bbc22c32df37620a7f30c1662e9 Mon Sep 17 00:00:00 2001
From: mgostIH <dennizmodesti@gmail.com>
Date: Thu, 2 Jul 2020 11:22:23 +0200
Subject: [PATCH 2/2] Fixed lints

---
 src/cb7.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/cb7.rs b/src/cb7.rs
index bac3d6f..822d15e 100644
--- a/src/cb7.rs
+++ b/src/cb7.rs
@@ -312,7 +312,7 @@ fn rsa_crypt(addr: &mut u32, val: &mut u32, rsakey: u64, modulus: u64) {
 
         while exp > 1 {
             if (exp & 1) == 1 {
-                acc = acc * base;
+                acc *= base;
                 acc %= modulus;
             }
             exp /= 2;
@@ -324,7 +324,7 @@ fn rsa_crypt(addr: &mut u32, val: &mut u32, rsakey: u64, modulus: u64) {
         // squaring the base afterwards is not necessary and may cause a
         // needless overflow.
         if exp == 1 {
-            acc = acc * base;
+            acc *= base;
         }
 
         (acc % modulus) as u64