optimize attack

src/main.rs

@@ -245,78 +245,51 @@ const TAC: [u64; 24] = [
     0xb38000003c800000,
 ];
 
-/// Binary search in a sorted slice of Tab by `output` field
+/// Full meet-in-the-middle attack (7‑bit u, 10‑bit w)
-fn binary_search_tab(table: &[Tab], target: u64) -> Option<&Tab> {
-    table
-        .binary_search_by(|entry| {
-            if entry.output < target {
-                Ordering::Less
-            } else if entry.output > target {
-                Ordering::Greater
-            } else {
-                Ordering::Equal
-            }
-        })
-        .ok()
-        .map(|idx| &table[idx])
-}
-
-/// Full meet-in-the-middle attack
 fn attack(z: u64) -> u64 {
-    const LOG_SIZE_TAC: u32 = 24;
+    const LOG_U: u32 = 7; // size of u space (bits)
-    const LOG_SIZE_KERB: u32 = 32;
+    const LOG_W: u32 = 10; // size of w space (bits)
-    let size_l = 1usize << LOG_SIZE_TAC;
+    let l_size = 1 << LOG_U;
+    let truev: u64 = 0; // v = 0
 
-    // Build table L (u -> stream( S = u XOR truev ) )
+    // --- Build table L (enumerate u) ---
-    let mut a0 = Lfsr { state: 0, mask: 0 };
+    let mut l: Vec<Tab> = Vec::with_capacity(l_size);
-    let mut b0 = Lfsr { state: 0, mask: 0 };
+    let mut current_gray: u64 = 0;
-    let mut c0 = Lfsr { state: 0, mask: 0 };
+    let mut s = truev;
-    init(0, &mut a0, &mut b0, &mut c0);
-    let stream0 = stream(&mut a0, &mut b0, &mut c0);
-    println!("[*] stream(S=0) = 0x{:016X}", stream0);
 
-    let mut l: Vec<Tab> = Vec::with_capacity(size_l);
+    // First entry u = 0
-
-    let truev: u64 = 0;
-
-    println!("[*] building L ({} entries)...", size_l);
-
-    let mut current_u = 0u64;
-    // First entry i=0
-    {
     let (mut a, mut b, mut c) = (
         Lfsr { state: 0, mask: 0 },
         Lfsr { state: 0, mask: 0 },
         Lfsr { state: 0, mask: 0 },
     );
-        init(current_u ^ truev, &mut a, &mut b, &mut c);
+    init(s, &mut a, &mut b, &mut c);
     l.push(Tab {
         output: stream(&mut a, &mut b, &mut c),
-            input: current_u,
+        input: 0,
     });
-    }
 
-    for i in 1u64..size_l as u64 {
+    // Remaining 2^LOG_U - 1 entries using Gray code + TAC
-        // Jump to next u using Gray-code XOR
+    for i in 1u64..l_size as u64 {
-        current_u ^= TAC[i.trailing_zeros() as usize];
+        let new_gray = i ^ (i >> 1);
+        let d = current_gray ^ new_gray;
+        let pos = d.trailing_zeros() as usize;
+        s ^= TAC[pos]; // update S = truev ^ u
+        current_gray = new_gray;
 
         let (mut a, mut b, mut c) = (
             Lfsr { state: 0, mask: 0 },
             Lfsr { state: 0, mask: 0 },
             Lfsr { state: 0, mask: 0 },
         );
-        init(current_u ^ truev, &mut a, &mut b, &mut c);
+        init(s, &mut a, &mut b, &mut c);
         l.push(Tab {
             output: stream(&mut a, &mut b, &mut c),
-            input: current_u,
+            input: s, // store the full S
         });
-
-        if i & 0xFFFFF == 0 {
-            println!("     {} / {}", i, size_l);
-        }
     }
 
-    println!("[*] Sorting L");
+    // Sort L by output for binary search
     l.sort_by(|a, b| {
         let cmp = a.output.cmp(&b.output);
         if cmp != Ordering::Equal {
@@ -325,60 +298,71 @@ fn attack(z: u64) -> u64 {
             a.input.cmp(&b.input)
         }
     });
-    println!("[*] Sort finished.");
 
-    println!("[*] Search in KerB");
+    // --- Search over w ---
-    let mut current_w = 0u64;
+    current_gray = 0;
-    let mut result = 0u64;
+    s = truev;
-    let mut found = false;
 
-    // First iteration w=0
+    // Base case w = 0
-    {
     let (mut a, mut b, mut c) = (
         Lfsr { state: 0, mask: 0 },
         Lfsr { state: 0, mask: 0 },
         Lfsr { state: 0, mask: 0 },
     );
-        init(current_w ^ truev, &mut a, &mut b, &mut c);
+    init(s, &mut a, &mut b, &mut c);
     let sw = stream(&mut a, &mut b, &mut c);
-        let target = z ^ sw ^ stream0;
+    let target = z ^ sw;
-        if let Some(hit) = binary_search_tab(&l, target) {
-            result = hit.input ^ current_w ^ truev;
-            found = true;
-            println!("[!] Correlation found ! w=0, u=0x{:016X}", hit.input);
-        }
-    }
 
-    for i in 1u64..(1u64 << LOG_SIZE_KERB) {
+    if let Ok(idx) = l.binary_search_by(|entry| {
-        if found {
+        if entry.output < target {
-            break;
+            Ordering::Less
-        }
+        } else if entry.output > target {
-        current_w ^= KER_B[i.trailing_zeros() as usize];
+            Ordering::Greater
-
-        let (mut a, mut b, mut c) = (
-            Lfsr { state: 0, mask: 0 },
-            Lfsr { state: 0, mask: 0 },
-            Lfsr { state: 0, mask: 0 },
-        );
-        init(current_w ^ truev, &mut a, &mut b, &mut c);
-        let sw = stream(&mut a, &mut b, &mut c);
-        let target = z ^ sw ^ stream0;
-
-        if let Some(hit) = binary_search_tab(&l, target) {
-            result = hit.input ^ current_w ^ truev;
-            found = true;
-            println!("[!] Correlation found at i={}", i);
-            println!("    w = 0x{:016X}", current_w);
-            println!("    u = 0x{:016X}", hit.input);
-        }
-    }
-
-    if !found {
-        println!("[-] Secret not found.");
-        0
         } else {
-        result
+            Ordering::Equal
         }
+    }) {
+        let hit = &l[idx];
+        // Secret = truev ^ w ^ stored_input
+        return s ^ hit.input;
+    }
+
+    // Iterate over the remaining 1023 values of w
+    let mut i = 1u64;
+    while i >> LOG_W == 0 {
+        let new_gray = i ^ (i >> 1);
+        let d = current_gray ^ new_gray;
+        let pos = d.trailing_zeros() as usize;
+        s ^= KER_B[pos]; // update S = truev ^ w
+        current_gray = new_gray;
+
+        let (mut a, mut b, mut c) = (
+            Lfsr { state: 0, mask: 0 },
+            Lfsr { state: 0, mask: 0 },
+            Lfsr { state: 0, mask: 0 },
+        );
+        init(s, &mut a, &mut b, &mut c);
+        let sw = stream(&mut a, &mut b, &mut c);
+        let target = z ^ sw;
+
+        if let Ok(idx) = l.binary_search_by(|entry| {
+            if entry.output < target {
+                Ordering::Less
+            } else if entry.output > target {
+                Ordering::Greater
+            } else {
+                Ordering::Equal
+            }
+        }) {
+            let hit = &l[idx];
+            return s ^ hit.input;
+        }
+
+        i += 1;
+    }
+
+    // Not found
+    0
 }
 
 //-------------------------- MAIN --------------------------
@@ -398,7 +382,7 @@ fn main() {
     println!("0x{:08X}", z);
 
     println!("key S = 0x{:016X}\n", s);
-    print_representation();
+    // print_representation();
 
     let plain: [u8; 8] = [b'H', b'E', b'L', b'L', b'O', b' ', b'W', b'O'];
     let message = pack8(&plain);
@@ -415,7 +399,7 @@ fn main() {
         std::str::from_utf8(&recovered_text[..8]).unwrap()
     );
 
-    let z_challenge: u64 = 0x2D0E339CFD588D1B;
+    let z_challenge: u64 = 0x9AC76518F2322DA4;
     println!("=== Meet-in-the-Middle attack===");
     println!("Target cipher stream : 0x{:016X}\n", z_challenge);
 
@@ -425,15 +409,4 @@ fn main() {
 
     println!("\nSecret found : S = 0x{:016X}", secret);
     println!("    Time : {:.2} s\n", elapsed);
-
-    // Verification
-    init(secret, &mut a, &mut b, &mut c);
-    let z_check = stream(&mut a, &mut b, &mut c);
-    println!("=== Check ===");
-    println!("stream(S_found)  = 0x{:016X}", z_check);
-    println!("z_challenge      = 0x{:016X}", z_challenge);
-    println!(
-        "Correlation   : {}",
-        if z_check == z_challenge { "YES" } else { "NO" }
-    );
 }