keyfork-shard: clean up documentation for encrypted shard padding

crates/keyfork-shard/src/lib.rs

@@ -25,9 +25,11 @@ use sha2::Sha256;
 use sharks::{Share, Sharks};
 use x25519_dalek::{EphemeralSecret, PublicKey};
 
-// 32-byte share, 1-byte index, 1-byte threshold, 1-byte version == 36 bytes
-// Encrypted, is 52 bytes
-const PLAINTEXT_LENGTH: u8 = 36;
+const PLAINTEXT_LENGTH: u8 = 32 // shard
+    + 1  // index
+    + 1  // threshold
+    + 1  // version
+    + 1; // length;
 const ENCRYPTED_LENGTH: u8 = PLAINTEXT_LENGTH + 16;
 
 #[cfg(feature = "openpgp")]
@@ -271,7 +273,7 @@ pub trait Format {
         payload.insert(1, threshold);
         assert!(
             payload.len() < PLAINTEXT_LENGTH as usize,
-            "invalid share length (too long, max {PLAINTEXT_LENGTH} bytes)"
+            "invalid share length (too long, must be less than {PLAINTEXT_LENGTH} bytes)"
         );
 
         // convert plaintext to static-size payload