things

prudpv0/src/crypto/common_crypto.rs

@@ -0,0 +1,54 @@
+trait IterExtra: Iterator {
+    fn sum_wrapping_u8(&mut self) -> u8
+    where
+        Self::Item: Into<u8>;
+
+    fn sum_wrapping_u32(&mut self) -> u32
+    where
+        Self::Item: Into<u32>;
+}
+
+impl<T: Iterator> IterExtra for T {
+    fn sum_wrapping_u8(&mut self) -> u8
+    where
+        Self::Item: Into<u8>,
+    {
+        let mut sum = 0u8;
+        for v in self {
+            let val: u8 = v.into();
+            sum = sum.wrapping_add(val);
+        }
+        sum
+    }
+    fn sum_wrapping_u32(&mut self) -> u32
+    where
+        Self::Item: Into<u32>,
+    {
+        let mut sum = 0u32;
+        for v in self {
+            let val: u32 = v.into();
+            sum = sum.wrapping_add(val);
+        }
+        sum
+    }
+}
+
+#[inline(always)]
+pub fn common_checksum(access_key: &str, data: &[u8]) -> u8 {
+    let leftover = data.len() % 4;
+    let word_sum = bytemuck::cast_slice::<_, u32>(&data[..data.len() - leftover])
+        .iter()
+        .copied()
+        .sum_wrapping_u32();
+
+    let checksum = access_key.as_bytes().iter().copied().sum_wrapping_u8();
+    let checksum = checksum.wrapping_add(
+        (&data[data.len() - leftover..])
+            .iter()
+            .copied()
+            .sum_wrapping_u8(),
+    );
+    let checksum = checksum.wrapping_add(word_sum.to_ne_bytes().into_iter().sum_wrapping_u8());
+
+    checksum
+}