linux-kernel - What is the purpose of "prologue" field used by kernel module signing script "sign-file"

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Message-ID: <CANBqPZ6LdUP-X=-1zJ3rBssdZ7VcwhqjqKHKe83ujKy_xnyE4w@mail.gmail.com>
Date:   Tue, 12 Dec 2017 16:01:18 +0530
From:   manisha verma <manisha.jnu08@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: What is the purpose of "prologue" field used by kernel module signing
 script "sign-file"

Hi,

I am going through the
/usr/src/kernels/3.10.0-693.el7.x86_64/scripts/sign-file code. I need
to understand the meaning of the “prologue” part in the script. The
script actually prefixes the prologue to the digest of the module file
and then signs it using the “openssl rsautl”.

Code snippet form
"/usr/src/kernels/3.10.0-693.el7.x86_64/scripts/sign-file" script

$prologue = pack(“C*”,
0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
0x05, 0x00, 0x04, 0x20);

Does anybody have any idea, what is the significance of this prologue?

Thanks,
Manisha