# OpenSSL Signature different each time

I have a file that I am generating a signature for using OpenSSL, and each time I generate the signature, it is different to the last time.

openssl dgst -sha1 -sign update_key.pem TERM010134.bin > Update.sig


Anyone able to tell me why that might be?

If the key is an RSA key, OpenSSL supports 3 RSA paddings other than none: pkcs1 (more exactly the type-1 scheme of PKCS#1 through v1.5, now retronymed RSASSA-PKCS1-v1_5), pss, and x931. dgst -sign for RSA defaults to pkcs, which is deterministic and should not produce varying results; if it does please edit your question with details (preferably using a test key). Only if you specify -sigopt rsa_padding_mode:pss should you get a randomized result.
Note RSA encryption is different, and OpenSSL supports two paddings other than none: pkcs1 (this time meaning RSAES-PKCS1-v1_5) and oaep, both of which are randomized; the newer OAEP is randomized in a way that is provably secure which the older v1_5 scheme does not.