HMAC-SHA1( secret key ) with header of a transmitted file Given: 
an AES-128 secret key (ASecKey) encrypts a file (CBC mode).
(Assume good random)

Is is insecure to append (include) an HMAC-SHA1 of ASecKey to file?

Purpose:
The receiver can then quickly verify if the shared secret key was used to encrypt.
It's probably better to use a KBKDF as that doesn't need a key as input. You can use the KDF as key check value or KCV. If you use a block cipher based KBKDF from NIST SP 800-108 then you could reuse the AES algorithm to calculate the KCV.

You could however also make it easy for yourself and use a SHA-1 or SHA-2 over the key as KCV.



Note that the PKCS#11 method allows for calculating a KCV by encrypting a block of all zero's; this method should not be used.