Sea Cipher 2

We found another message that seems to be encoded with the Sea Cipher method, but the key has been changed! We have the {{encrypted_book.txt, encrypted book}} and the {{cipher, encryption program}}, this time with the secret key redacted. Could you decrypt this for us, please?
dnszyh_mx_xkx_jr_sllhnyh_tcqjhgiv

Use flagCheck to input the flag you get from the challenge to get the actual flag

If you need hint than cat /challenge/hint.txt