add epk3 initial support , move epk common functions

src/formats/epk.rs

@@ -51,8 +51,56 @@ pub fn extract_epk(file: &File, output_folder: &str) -> Result<(), Box<dyn std::
         println!("EPK2 detected!\n");
         formats::epk2::extract_epk2(file, output_folder)?;
     } else if epk_version == Some("epk3".to_string()) {
-        println!("EPK3 detected! Not supported yet.");
+        println!("EPK3 detected!\n");
+        formats::epk3::extract_epk3(file, output_folder)?;
     }
 
     Ok(())
+}
+
+//COMMON EPK FUNCTIONS
+pub fn find_key<'a>(key_array: &'a [(&'a str, &'a str)], data: &[u8], expected_magic: &[u8]) -> Result<Option<(&'a str, Vec<u8>)>, Box<dyn std::error::Error>> {
+    for (key_hex, name) in key_array {
+        let key_bytes = hex::decode(key_hex)?;
+        let decrypted = match decrypt_aes_ecb_auto(&key_bytes, data) {
+            Ok(d) => d,
+            Err(_) => continue,
+        };
+     
+        if decrypted.starts_with(expected_magic) {
+            return Ok(Some((name, key_bytes)));
+        }
+    }
+    Ok(None)
+}
+
+use aes::Aes128;
+use aes::Aes256;
+use ecb::{Decryptor, cipher::{BlockDecryptMut, KeyInit, generic_array::GenericArray}};
+
+type Aes128EcbDec = Decryptor<Aes128>;
+type Aes256EcbDec = Decryptor<Aes256>;
+
+pub fn decrypt_aes_ecb_auto(key: &[u8], ciphertext: &[u8]) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
+    let mut buffer = ciphertext.to_vec();
+
+    if key.len() == 32 {
+        // aes256
+        let key_array: [u8; 32] = key.try_into()?;
+        let mut decryptor = Aes256EcbDec::new(&key_array.into());
+        for chunk in buffer.chunks_exact_mut(16) {
+            let block: &mut [u8; 16] = chunk.try_into()?;
+            decryptor.decrypt_block_mut(GenericArray::from_mut_slice(block));
+        }
+    } else {
+        // aes128
+        let key_array: [u8; 16] = key.try_into()?;
+        let mut decryptor = Aes128EcbDec::new(&key_array.into());
+        for chunk in buffer.chunks_exact_mut(16) {
+            let block: &mut [u8; 16] = chunk.try_into()?;
+            decryptor.decrypt_block_mut(GenericArray::from_mut_slice(block));
+        }
+    }
+
+    Ok(buffer)
 }