SQL Server

Create a DKIM-Signature for a MIME Message

Demonstrates the Chilkat Dkim.DkimSign method, which creates a DKIM-Signature header and prepends it to a complete MIME message held in a BinData, modifying it in place. The DkimAlg, DkimCanon, DkimDomain, DkimSelector, DkimHeaders, and DkimBodyLengthCount properties configure the generated signature.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: The signature is computed over a hash of the body plus a chosen set of headers, so the message must be completely built — every header, encoding, and boundary — before signing; any later change invalidates it. The d= (domain) and s= (selector) tags tell a verifier where to find the public key: at selector._domainkey.domain in DNS. relaxed/relaxed canonicalization tolerates the minor whitespace changes mail systems make in transit, which is why it is the common choice.

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--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    --  Demonstrates the Dkim.DkimSign method, which creates a DKIM-Signature header and prepends it to
    --  a complete MIME message.  The only argument is a BinData holding the MIME, which is modified in
    --  place.
    --  
    --  The DkimAlg, DkimCanon, DkimDomain, DkimSelector, DkimHeaders, and DkimBodyLengthCount
    --  properties configure the signature that is generated.

    DECLARE @dkim int
    EXEC @hr = sp_OACreate 'Chilkat.Dkim', @dkim OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    --  Configure the DKIM signature.
    EXEC sp_OASetProperty @dkim, 'DkimDomain', 'example.com'
    EXEC sp_OASetProperty @dkim, 'DkimSelector', 'myselector'

    --  Signing algorithm written to the a= tag.
    EXEC sp_OASetProperty @dkim, 'DkimAlg', 'rsa-sha256'

    --  Canonicalization for headers and body, written to the c= tag.
    EXEC sp_OASetProperty @dkim, 'DkimCanon', 'relaxed/relaxed'

    --  Colon-separated list of header fields to sign, written to the h= tag.
    EXEC sp_OASetProperty @dkim, 'DkimHeaders', 'From:To:Subject:Date:Message-ID'

    --  Maximum number of canonicalized body bytes to hash.  0 means the entire body.
    EXEC sp_OASetProperty @dkim, 'DkimBodyLengthCount', 0

    --  Load the RSA private key and give it to the Dkim object.
    DECLARE @privKey int
    EXEC @hr = sp_OACreate 'Chilkat.PrivateKey', @privKey OUT

    EXEC sp_OAMethod @privKey, 'LoadPemFile', @success OUT, 'qa_data/dkim_private.pem'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @privKey, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @dkim
        EXEC @hr = sp_OADestroy @privKey
        RETURN
      END
    EXEC sp_OAMethod @dkim, 'SetDkimPrivateKey', @success OUT, @privKey
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @dkim, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @dkim
        EXEC @hr = sp_OADestroy @privKey
        RETURN
      END

    --  Load the complete MIME message to be signed.  It must already contain all headers, transfer
    --  encodings, MIME boundaries, and body bytes.
    DECLARE @mimeData int
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @mimeData OUT

    EXEC sp_OAMethod @mimeData, 'LoadFile', @success OUT, 'qa_data/message.eml'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @mimeData, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @dkim
        EXEC @hr = sp_OADestroy @privKey
        EXEC @hr = sp_OADestroy @mimeData
        RETURN
      END

    --  Sign.  The DKIM-Signature header is prepended to the MIME in place.
    EXEC sp_OAMethod @dkim, 'DkimSign', @success OUT, @mimeData
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @dkim, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @dkim
        EXEC @hr = sp_OADestroy @privKey
        EXEC @hr = sp_OADestroy @mimeData
        RETURN
      END

    --  Save the signed message.
    EXEC sp_OAMethod @mimeData, 'WriteFile', @success OUT, 'qa_output/signed.eml'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @mimeData, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @dkim
        EXEC @hr = sp_OADestroy @privKey
        EXEC @hr = sp_OADestroy @mimeData
        RETURN
      END

    PRINT 'Message signed.'

    EXEC @hr = sp_OADestroy @dkim
    EXEC @hr = sp_OADestroy @privKey
    EXEC @hr = sp_OADestroy @mimeData


END
GO