From 3de3440f168accd9e9ebf38119fa64fe0a308309 Mon Sep 17 00:00:00 2001
From: Kristofers Solo <dev@kristofers.xyz>
Date: Sun, 23 Nov 2025 18:23:19 +0200
Subject: [PATCH] feat(aes): add inverse SBox lookup

---
 aes/src/aes.rs            |  3 +-
 aes/src/block/block128.rs |  3 ++
 aes/src/constants.rs      | 69 ++++++++++++++++++++++++++++++++++++++-
 aes/src/sbox.rs           | 13 +++++++-
 4 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/aes/src/aes.rs b/aes/src/aes.rs
index 6be43e6..66f5d79 100644
--- a/aes/src/aes.rs
+++ b/aes/src/aes.rs
@@ -59,9 +59,8 @@ fn substitute_bytes(block: Block128) -> Block128 {
 
 #[cfg(test)]
 mod tests {
-    use rstest::rstest;
-
     use super::*;
+    use rstest::rstest;
 
     const TEST_MESSAGE: u128 = 0x0123_4567_89AB_CDEF_FEDC_BA98_7654_3210;
 
diff --git a/aes/src/block/block128.rs b/aes/src/block/block128.rs
index a65bebc..33474a8 100644
--- a/aes/src/block/block128.rs
+++ b/aes/src/block/block128.rs
@@ -26,6 +26,9 @@ impl SboxLookup for Block128 {
     fn sbox_lookup(self) -> Self {
         Self(self.0.sbox_lookup())
     }
+    fn inv_sbox_lookup(self) -> Self {
+        Self(self.0.inv_sbox_lookup())
+    }
 }
 
 impl Block128 {
diff --git a/aes/src/constants.rs b/aes/src/constants.rs
index 157ad6b..7409883 100644
--- a/aes/src/constants.rs
+++ b/aes/src/constants.rs
@@ -1,4 +1,4 @@
-// AES Constants
+//! AES Constants
 pub const S_BOXES: [[u8; 16]; 16] = [
     [
         0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB,
@@ -66,6 +66,73 @@ pub const S_BOXES: [[u8; 16]; 16] = [
     ],
 ];
 
+pub const INV_S_BOXES: [[u8; 16]; 16] = [
+    [
+        0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7,
+        0xFB,
+    ],
+    [
+        0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9,
+        0xCB,
+    ],
+    [
+        0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3,
+        0x4E,
+    ],
+    [
+        0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1,
+        0x25,
+    ],
+    [
+        0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6,
+        0x92,
+    ],
+    [
+        0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D,
+        0x84,
+    ],
+    [
+        0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45,
+        0x06,
+    ],
+    [
+        0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A,
+        0x6B,
+    ],
+    [
+        0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6,
+        0x73,
+    ],
+    [
+        0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF,
+        0x6E,
+    ],
+    [
+        0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE,
+        0x1B,
+    ],
+    [
+        0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A,
+        0xF4,
+    ],
+    [
+        0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC,
+        0x5F,
+    ],
+    [
+        0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C,
+        0xEF,
+    ],
+    [
+        0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99,
+        0x61,
+    ],
+    [
+        0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C,
+        0x7D,
+    ],
+];
+
 pub const RCON: [u32; 10] = [
     0x0100_0000,
     0x0200_0000,
diff --git a/aes/src/sbox.rs b/aes/src/sbox.rs
index 7a51f0d..1e56b41 100644
--- a/aes/src/sbox.rs
+++ b/aes/src/sbox.rs
@@ -1,7 +1,8 @@
-use crate::constants::S_BOXES;
+use crate::constants::{INV_S_BOXES, S_BOXES};
 
 pub trait SboxLookup: Sized {
     fn sbox_lookup(self) -> Self;
+    fn inv_sbox_lookup(self) -> Self;
 }
 
 macro_rules! impl_sbox_lookup {
@@ -16,6 +17,16 @@ macro_rules! impl_sbox_lookup {
                     acc | Self::from(S_BOXES[row][col]) << shift
                 })
             }
+
+            fn inv_sbox_lookup(self) -> Self {
+                (0..$bytes).fold(0, |acc, idx| {
+                    let shift = ($bytes - 1 - idx) * 8;
+                    let byte = ((self >> shift) & 0xFF) as u8;
+                    let row = (byte >> 4) as usize;
+                    let col = (byte & 0xF) as usize;
+                    acc | Self::from(INV_S_BOXES[row][col]) << shift
+                })
+            }
         }
     };
 }