From 8dbb80604d95ae51d8ee87b21cf7e0880e90486a Mon Sep 17 00:00:00 2001
From: Paolo Barbolini <paolo.barbolini@m4ss.net>
Date: Tue, 9 Apr 2024 09:29:23 +0200
Subject: [PATCH] Fix broken CRC handling

Signed-off-by: Paolo Barbolini <paolo.barbolini@m4ss.net>
---
 src/crc.rs | 26 ++++++++++++++++++++++++--
 src/lib.rs | 23 +++++++++--------------
 2 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/src/crc.rs b/src/crc.rs
index 07d8bd2..2f501a8 100644
--- a/src/crc.rs
+++ b/src/crc.rs
@@ -38,7 +38,7 @@ pub(crate) fn crc16(data: &[u8]) -> u16 {
 }
 
 pub(crate) fn valid_checksum(data: &[u8], expected: u16) -> bool {
-    crc16(data) != expected
+    crc16(data) == expected
 }
 
 pub(crate) fn push_crc(data: &mut Vec<u8>) {
@@ -54,7 +54,29 @@ pub(crate) fn extract_crc(data: &mut Vec<u8>) -> Result<u16> {
         )
     })?;
 
-    let crc = u16::from_le_bytes(data[..2].try_into().unwrap());
+    let crc = u16::from_le_bytes(data[data_len..].try_into().unwrap());
     data.truncate(data_len);
     Ok(crc)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{crc16, extract_crc, push_crc, valid_checksum};
+
+    #[test]
+    fn e2e() {
+        let mut raw_data = rand::random::<[u8; 32]>();
+        let data_crc = crc16(&raw_data);
+
+        let mut data = raw_data.to_vec();
+        push_crc(&mut data);
+
+        let crc = extract_crc(&mut data).unwrap();
+        assert_eq!(raw_data, data.as_slice());
+        assert_eq!(data_crc, crc);
+        assert!(valid_checksum(&raw_data, data_crc));
+
+        raw_data[17] = raw_data[17].wrapping_sub(1);
+        assert!(!valid_checksum(&raw_data, data_crc));
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index d4b2937..2c27f1f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -452,7 +452,7 @@ mod tests {
 
     #[test]
     fn from_seed_rejects_bad_prefix() {
-        let seed = "FAAPN4W3EG6KCJGUQTKTJ5GSB5NHK5CHAJL4DBGFUM3HHROI4XUEP4OBK4";
+        let seed = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
         let pair = KeyPair::from_seed(seed);
         assert!(pair.is_err());
         if let Err(e) = pair {
@@ -460,20 +460,15 @@ mod tests {
         }
     }
 
-    /*
-    * TODO - uncomment this test when I can figure out how to encode a bad checksum
-     * without first triggering a base32 decoding failure :)
-
-        #[test]
-        fn from_seed_rejects_bad_checksum() {
-            let seed = "SAAPN4W3EG6KCJGUQTKTJ5GSB5NHK5CHAJL4DBGFUM3HHROI4XUEP4OBK4";
-            let pair = KeyPair::from_seed(seed);
-            assert!(pair.is_err());
-            if let Err(e) = pair {
-                assert_eq!(e.kind(), ErrorKind::ChecksumFailure);
-            }
+    #[test]
+    fn from_seed_rejects_bad_checksum() {
+        let seed = "FAAPN4W3EG6KCJGUQTKTJ5GSB5NHK5CHAJL4DBGFUM3HHROI4XUEP4OBK4";
+        let pair = KeyPair::from_seed(seed);
+        assert!(pair.is_err());
+        if let Err(e) = pair {
+            assert_eq!(e.kind(), ErrorKind::ChecksumFailure);
         }
-    */
+    }
 
     #[test]
     fn from_seed_rejects_bad_length() {