PureBasic

Create an Opaque (Attached) S/MIME Signature

Demonstrates the Chilkat Mime.ConvertToSigned method, which creates an opaque (attached) S/MIME signature. The only argument is the signing Cert. On success the entity is replaced by a CMS/PKCS #7 signed-data structure that wraps the content inside the 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: An opaque signature bundles the content inside the CMS structure, so the message is a single application/pkcs7-mime blob that only S/MIME-aware software can read. It is more tamper-resistant in transit — nothing can alter the content without breaking the wrapper — at the cost of the backward compatibility a detached signature offers. Use it when every recipient is known to support S/MIME.

Chilkat PureBasic Downloads

Download Chilkat for PureBasic

PureBasic

IncludeFile "CkCert.pb"
IncludeFile "CkMime.pb"

Procedure ChilkatExample()

    success.i = 0

    mime.i = CkMime::ckCreate()
    If mime.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkMime::ckSetBodyFromPlainText(mime,"This message will be signed.")
    If success = 0
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        ProcedureReturn
    EndIf

    ;  Load the signing certificate (which must have access to its private key) from a PFX file.
    ;  The PFX password should come from a secure source rather than being hard-coded.
    pfxPassword.s = "myPfxPassword"
    cert.i = CkCert::ckCreate()
    If cert.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkCert::ckLoadPfxFile(cert,"qa_data/signer.pfx",pfxPassword)
    If success = 0
        Debug CkCert::ckLastErrorText(cert)
        CkMime::ckDispose(mime)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    ;  Create an OPAQUE (attached) S/MIME signature.  The entity is replaced by a CMS/PKCS #7
    ;  signed-data structure that wraps the content inside the signature.
    success = CkMime::ckConvertToSigned(mime,cert)
    If success = 0
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    success = CkMime::ckSaveMime(mime,"qa_output/signed_opaque.eml")
    If success = 0
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    Debug "Message converted to an opaque signed message."


    CkMime::ckDispose(mime)
    CkCert::ckDispose(cert)


    ProcedureReturn
EndProcedure