diff --git a/src/lib.rs b/src/lib.rs
index f1b0d88..82316b7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,10 @@
+use std::sync::{Mutex, MutexGuard};
+use std::fmt::Debug;
+
 pub use sp_client;
 pub use uuid;
 pub use log;
+pub use aes_gcm;
 
 pub mod crypto;
 pub mod device;
@@ -11,3 +15,16 @@ pub mod prd;
 pub mod process;
 pub mod silentpayments;
 pub mod signature;
+
+pub const MAX_PRD_PAYLOAD_SIZE: usize = u16::MAX as usize; // 64KiB sounds reasonable for now
+
+pub trait MutexExt<T> {
+    fn lock_anyhow(&self) -> Result<MutexGuard<T>, anyhow::Error>;
+}
+
+impl<T: Debug> MutexExt<T> for Mutex<T> {
+    fn lock_anyhow(&self) -> Result<MutexGuard<T>, anyhow::Error> {
+        self.lock()
+            .map_err(|e| anyhow::Error::msg(format!("Failed to lock: {}", e)))
+    }
+}