From a83767f9fbd51df654901b52bdba7838f6a10bf9 Mon Sep 17 00:00:00 2001
From: Igor Tolmachev <me@igorek.dev>
Date: Tue, 16 Jul 2024 01:59:53 +0900
Subject: Add traditional PKWARE decryption.

    - Compression and encryption may not work together
    - Password check is not yet implemented
    - Unoptimized crc32 function
---
 src/zip/encryption.rs | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 src/zip/encryption.rs

(limited to 'src/zip/encryption.rs')

diff --git a/src/zip/encryption.rs b/src/zip/encryption.rs
new file mode 100644
index 0000000..84e30d5
--- /dev/null
+++ b/src/zip/encryption.rs
@@ -0,0 +1,62 @@
+use crate::utils::ReadUtils;
+use crate::zip::ZipResult;
+use crc32fast::Hasher;
+use std::io::{Read, Result as IoResult};
+
+fn crc32(byte: u8, crc32: u32) -> u32 {
+    let mut hasher = Hasher::new_with_initial(crc32 ^ 0xFFFFFFFF);
+    hasher.update(&[byte]);
+    hasher.finalize() ^ 0xFFFFFFFF
+}
+
+pub struct WeakDecoder<Io: Read> {
+    key0: u32,
+    key1: u32,
+    key2: u32,
+    io: Io,
+}
+
+impl<Io: Read> WeakDecoder<Io> {
+    pub fn new(io: Io, password: &str) -> ZipResult<Self> {
+        let mut decoder = Self {
+            key0: 305419896,
+            key1: 591751049,
+            key2: 878082192,
+            io,
+        };
+
+        for c in password.chars() {
+            decoder.update_keys(c as u8)
+        }
+
+        let buf = decoder.read_arr::<12>()?;
+
+        Ok(decoder)
+    }
+
+    fn update_keys(&mut self, byte: u8) {
+        self.key0 = crc32(byte, self.key0);
+        self.key1 = self
+            .key1
+            .wrapping_add(self.key0 & 0xFF)
+            .wrapping_mul(134775813)
+            .wrapping_add(1);
+        self.key2 = crc32((self.key1 >> 24) as u8, self.key2);
+    }
+
+    fn decode_byte(&mut self, byte: u8) -> u8 {
+        let key = self.key2 | 2;
+        byte ^ (((key * (key ^ 1)) >> 8) as u8)
+    }
+}
+
+impl<Io: Read> Read for WeakDecoder<Io> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<usize> {
+        let bytes = self.io.read(buf)?;
+        for i in 0..bytes {
+            buf[i] = self.decode_byte(buf[i]);
+            self.update_keys(buf[i])
+        }
+        Ok(bytes)
+    }
+}
-- 
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