crypto/aes: more precise description for AES keys

src/crypto/aes/aes.go

@@ -30,7 +30,7 @@ func (k KeySizeError) Error() string {
 }
 
 // NewCipher creates and returns a new [cipher.Block].
-// The key argument should be the AES key,
+// The key argument must be the AES key,
 // either 16, 24, or 32 bytes to select
 // AES-128, AES-192, or AES-256.
 func NewCipher(key []byte) (cipher.Block, error) {