How to generate DKIM-Signature in C++ Builder email header?

Question

C++ / C#

There is a domain, private and public keys are obtained from the site dkimcore.org/. TXT record added to dns, but what to do next? I am writing my own smtp server using c++ Builder RAD STUDIO. I so understand, it is necessary to form record of type:
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=desconto.ru; [email protected]; q=dns/txt; s=selector; t=1349850018; h=Content-Type : MIME-Version : Content-Transfer-Encoding : Subject : From : To : Date : Message-ID; bh=Kaikl4ete0nNVshtijtar0QktbxYsi5bvpy0llJ0cv4=; b=mzRM/VdOzSbO+BM1aLyIavOebQqx8+m1Vqy4BmJqGc0vRcbMlnROWqxrWndF2BSUujSuKlXkS7crij6NxAEcvg==
How to get bh and b?

Answer 1

"v=" - version of the DKIM specification
"a=" - algorithm for calculating the signature
"c=" - canonicalization algorithm,
"d=" - responsible for sending the letter (usually the sender's domain)
"q=" - methods for obtaining the public key
"s= " - selector separating namespaces in "d="
"t=" - timestamp
"h=" - signed fields
"b=" - signature
itself "bh=" - hash of canonicalized representation of message body
Detailed in RFC6736

Answer 2

Thank you, but can you be a little more detailed about b and bh. Specifically, how they can be generated and where to get them from.