diff --git a/mls-rs-codec/src/lib.rs b/mls-rs-codec/src/lib.rs
index c6d754b8..72e66c23 100644
--- a/mls-rs-codec/src/lib.rs
+++ b/mls-rs-codec/src/lib.rs
@@ -50,6 +50,8 @@ pub enum Error {
     UnsupportedEnumDiscriminant,
     #[cfg_attr(feature = "std", error("Expected UTF-8 string"))]
     Utf8,
+    #[cfg_attr(feature = "std", error("Invalid content"))]
+    InvalidContent,
     #[cfg_attr(feature = "std", error("mls codec error: {0}"))]
     Custom(u8),
 }
diff --git a/mls-rs-codec/src/map.rs b/mls-rs-codec/src/map.rs
index 9c7f3bec..c71244ff 100644
--- a/mls-rs-codec/src/map.rs
+++ b/mls-rs-codec/src/map.rs
@@ -43,7 +43,13 @@ where
             let mut items = HashMap::new();
 
             while !data.is_empty() {
-                items.insert(K::mls_decode(data)?, V::mls_decode(data)?);
+                let before = data.len();
+                let key = K::mls_decode(data)?;
+                let value = V::mls_decode(data)?;
+
+                if data.len() == before || items.insert(key, value).is_some() {
+                    return Err(crate::Error::InvalidContent);
+                }
             }
 
             Ok(items)
@@ -81,10 +87,241 @@ where
             let mut items = BTreeMap::new();
 
             while !data.is_empty() {
-                items.insert(K::mls_decode(data)?, V::mls_decode(data)?);
+                let before = data.len();
+                let key = K::mls_decode(data)?;
+                let value = V::mls_decode(data)?;
+
+                if data.len() == before || items.insert(key, value).is_some() {
+                    return Err(crate::Error::InvalidContent);
+                }
             }
 
             Ok(items)
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{MlsDecode, MlsEncode};
+    use assert_matches::assert_matches;
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_basic_hashmap_roundtrip() {
+        let mut original = HashMap::new();
+        original.insert(1u32, 100);
+        original.insert(2u32, 200);
+        original.insert(3u32, 300);
+        original.insert(4u32, 100);
+
+        let mut encoded = Vec::new();
+        original.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = HashMap::<u32, u32>::mls_decode(&mut slice).unwrap();
+
+        assert_eq!(original, decoded);
+        assert!(slice.is_empty());
+    }
+
+    #[test]
+    fn test_basic_btreemap_roundtrip() {
+        let mut original = BTreeMap::new();
+        original.insert(1u32, 100);
+        original.insert(2u32, 200);
+        original.insert(3u32, 300);
+        original.insert(4u32, 100);
+
+        let mut encoded = Vec::new();
+        original.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = BTreeMap::<u32, u32>::mls_decode(&mut slice).unwrap();
+
+        assert_eq!(original, decoded);
+        assert!(slice.is_empty());
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_empty_structure_in_hashmap() {
+        let mut original: HashMap<u8, [u8; 0]> = HashMap::new();
+        original.insert(1u8, []);
+        original.insert(2u8, []);
+
+        let mut encoded = Vec::new();
+        original.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = HashMap::<u8, [u8; 0]>::mls_decode(&mut slice).unwrap();
+        assert_eq!(original, decoded);
+        assert!(slice.is_empty());
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn hashmap_zero_length_structure() {
+        let res = HashMap::<[u8; 0], [u8; 0]>::mls_decode(&mut &[0x01, 0xff][..]);
+        assert_matches!(res, Err(crate::Error::InvalidContent))
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn hashmap_will_not_allow_duplicate_keys() {
+        let mut encoded = Vec::new();
+
+        vec![(1u8, 2u8), (3u8, 4u8), (1u8, 5u8)]
+            .mls_encode(&mut encoded)
+            .unwrap();
+
+        let res = HashMap::<u8, u8>::mls_decode(&mut &*encoded);
+        assert_matches!(res, Err(crate::Error::InvalidContent))
+    }
+
+    #[test]
+    fn btree_map_will_not_allow_duplicate_keys() {
+        let mut encoded = Vec::new();
+
+        vec![(1u8, 2u8), (3u8, 4u8), (1u8, 5u8)]
+            .mls_encode(&mut encoded)
+            .unwrap();
+
+        let res = BTreeMap::<u8, u8>::mls_decode(&mut &*encoded);
+        assert_matches!(res, Err(crate::Error::InvalidContent))
+    }
+
+    #[test]
+    fn btree_map_zero_length_structure() {
+        let res = BTreeMap::<[u8; 0], [u8; 0]>::mls_decode(&mut &[0x01, 0xff][..]);
+        assert_matches!(res, Err(crate::Error::InvalidContent))
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_hashmap_encoding_order() {
+        let mut hash = HashMap::new();
+        hash.insert(3u32, "c".to_string());
+        hash.insert(1u32, "a".to_string());
+        hash.insert(2u32, "b".to_string());
+
+        let mut btree = BTreeMap::new();
+        btree.insert(3u32, "c".to_string());
+        btree.insert(1u32, "a".to_string());
+        btree.insert(2u32, "b".to_string());
+
+        let mut hash_encoded = Vec::new();
+        hash.mls_encode(&mut hash_encoded).unwrap();
+
+        let mut btree_encoded = Vec::new();
+        btree.mls_encode(&mut btree_encoded).unwrap();
+
+        assert_eq!(hash_encoded, btree_encoded);
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_empty_hashmap() {
+        let empty_hash: HashMap<u32, u32> = HashMap::new();
+        let mut encoded = Vec::new();
+        empty_hash.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = HashMap::<u32, u32>::mls_decode(&mut slice).unwrap();
+        assert!(decoded.is_empty());
+        assert!(slice.is_empty());
+    }
+
+    #[test]
+    fn test_empty_btreemap() {
+        let empty_btree: BTreeMap<u32, u32> = BTreeMap::new();
+        let mut encoded = Vec::new();
+        empty_btree.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = BTreeMap::<u32, u32>::mls_decode(&mut slice).unwrap();
+        assert!(decoded.is_empty());
+        assert!(slice.is_empty());
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_large_hashmap() {
+        let mut large_map = HashMap::new();
+        for i in 0..1000u32 {
+            large_map.insert(i, i * 2);
+        }
+
+        let mut encoded = Vec::new();
+        large_map.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = HashMap::<u32, u32>::mls_decode(&mut slice).unwrap();
+
+        assert_eq!(large_map, decoded);
+        assert!(slice.is_empty());
+    }
+
+    #[test]
+    fn test_large_btreemap() {
+        let mut large_map = BTreeMap::new();
+        for i in 0..1000u32 {
+            large_map.insert(i, i * 2);
+        }
+
+        let mut encoded = Vec::new();
+        large_map.mls_encode(&mut encoded).unwrap();
+
+        let mut slice = encoded.as_slice();
+        let decoded = BTreeMap::<u32, u32>::mls_decode(&mut slice).unwrap();
+
+        assert_eq!(large_map, decoded);
+        assert!(slice.is_empty());
+    }
+
+    #[test]
+    fn test_invalid_btreemap_decode() {
+        // Test with invalid data
+        let invalid_data = vec![0xFF, 0xFF, 0xFF, 0xFF]; // Invalid length prefix
+        let mut slice = invalid_data.as_slice();
+
+        let result = BTreeMap::<u32, u32>::mls_decode(&mut slice);
+        assert!(result.is_err());
+
+        // Test with truncated data
+        let mut valid_map = BTreeMap::new();
+        valid_map.insert(1u32, 100u32);
+
+        let mut encoded = Vec::new();
+        valid_map.mls_encode(&mut encoded).unwrap();
+        encoded.truncate(encoded.len() - 1); // Remove last byte
+
+        let mut slice = encoded.as_slice();
+        let result = BTreeMap::<u32, u32>::mls_decode(&mut slice);
+        assert!(result.is_err());
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn test_invalid_hashmap_decode() {
+        // Test with invalid data
+        let invalid_data = vec![0xFF, 0xFF, 0xFF, 0xFF]; // Invalid length prefix
+        let mut slice = invalid_data.as_slice();
+
+        let result = HashMap::<u32, u32>::mls_decode(&mut slice);
+        assert!(result.is_err());
+
+        // Test with truncated data
+        let mut valid_map = HashMap::new();
+        valid_map.insert(1u32, 100u32);
+
+        let mut encoded = Vec::new();
+        valid_map.mls_encode(&mut encoded).unwrap();
+        encoded.truncate(encoded.len() - 1); // Remove last byte
+
+        let mut slice = encoded.as_slice();
+        let result = HashMap::<u32, u32>::mls_decode(&mut slice);
+        assert!(result.is_err());
+    }
+}
diff --git a/mls-rs-codec/src/vec.rs b/mls-rs-codec/src/vec.rs
index 3d7f1a8a..05a47a36 100644
--- a/mls-rs-codec/src/vec.rs
+++ b/mls-rs-codec/src/vec.rs
@@ -53,7 +53,14 @@ where
             let mut items = Vec::new();
 
             while !data.is_empty() {
-                items.push(T::mls_decode(data)?);
+                let before = data.len();
+                let value = T::mls_decode(data)?;
+
+                if data.len() == before {
+                    return Err(crate::Error::InvalidContent);
+                }
+
+                items.push(value);
             }
 
             Ok(items)
@@ -97,4 +104,10 @@ mod tests {
             Err(Error::UnexpectedEOF)
         );
     }
+
+    #[test]
+    fn vec_zero_length_structure() {
+        let res = Vec::<[u8; 0]>::mls_decode(&mut &[0x01, 0xff][..]);
+        assert_matches!(res, Err(crate::Error::InvalidContent))
+    }
 }
diff --git a/mls-rs-crypto-rustcrypto/Cargo.toml b/mls-rs-crypto-rustcrypto/Cargo.toml
index 4d2c814a..cb2fe324 100644
--- a/mls-rs-crypto-rustcrypto/Cargo.toml
+++ b/mls-rs-crypto-rustcrypto/Cargo.toml
@@ -43,6 +43,7 @@ rand_core = { version = "0.6", default-features = false, features = ["alloc"] }
 # AEAD
 aes-gcm = { version = "0.10", features = ["zeroize"] }
 chacha20poly1305 = { version = "0.10", default-features = false, features = ["alloc", "getrandom"] }
+generic-array = { version = "=0.14.7", default-features = false }
 aead = { version = "0.5", default-features = false, features = ["alloc", "getrandom"] }
 
 # Hash