PureBasic

Decrypt S/MIME and Verify S/MIME Signatures

See more MIME Examples

_LANGUAGE_ example to decrypt S/MIME and verify S/MIME signatures. The S/MIME is unwrapped to get the original MIME prior to signing/encrypting. PureBasic

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

Procedure ChilkatExample()

    success.i = 0

    ; This example requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

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

    ; Load an S/MIME message from a file:
    success = CkMime::ckLoadMimeFile(mime,"signedMime.txt")
    If success = 0
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        ProcedureReturn
    EndIf

    ; The ContainsEncryptedParts/ContainsSignedParts methods
    ; can be called to determine if the MIME is encrypted and/or signed:
    isEncrypted.i = CkMime::ckContainsEncryptedParts(mime)
    isSigned.i = CkMime::ckContainsSignedParts(mime)

    ; We don't want the "unwrap extras".  You'll see what those
    ; are in a few moments...
    CkMime::setCkUnwrapExtras(mime, 0)

    ; To verify the signature, call UnwrapSecurity.  This will
    ; verify the signature(s) and decrypt the S/MIME and restore
    ; the MIME to the unsigned/unencrypted state.
    ; The results of what was found are present in the MIME object's
    ; properties, as well as extra header fields that are added
    ; to the unwrapped MIME.
    success = CkMime::ckUnwrapSecurity(mime)
    If success <> 1
        ; UnwrapSecurity returns 1 if all signatures were
        ; verified and all parts decrypted.
        Debug CkMime::ckLastErrorText(mime)
        CkMime::ckDispose(mime)
        ProcedureReturn
    EndIf

    ; The mime.UnwrapExtras property controls whether or not
    ; these additional fields are added to the unwrapped MIME:
    ; 
    ; X-NumPartsSigned: 1
    ; X-SignaturesValid: yes
    ; X-NumPartsEncrypted: 1
    ; X-Decrypted: no
    ; 
    ; The X-NumPartsSigned/X-SignaturesValid headers are added
    ; if the MIME was signed.  
    ; 
    ; The X-NumPartsEncrypted/X-Decrypted headers are added
    ; if the MIME was encrypted.
    ; 

    ; If the MIME was signed, get the certificate used for signing.
    If isSigned = 1
        signerCert.i = CkCert::ckCreate()
        If signerCert.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        ; The NumSignerCerts property indicates how many certificates
        ; were used for signing.  This example will assume the value is 1.
        ; To get the 1st signer cert, call LastSignerCert with an index of 0:
        success = CkMime::ckLastSignerCert(mime,0,signerCert)
        If success = 1
            Debug "**** Signer Cert: " + CkCert::ckSubjectCN(signerCert)
        EndIf

    EndIf

    ; If the MIME was encrypted, get the certificate used for decryption
    If isEncrypted = 1
        ; The NumDecryptCerts property indicates how many certificates
        ; were used for decrypting.  This example will assume the value is 1.
        ; To get the 1st decrypt cert, call LastDecryptCert with an index of 0:
        decryptCert.i = CkCert::ckCreate()
        If decryptCert.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        success = CkMime::ckLastDecryptCert(mime,0,decryptCert)
        If success = 1
            Debug "**** Decrypt Cert: " + CkCert::ckSubjectCN(decryptCert)
        EndIf

    EndIf

    ; Display the unwrapped MIME:
    Debug CkMime::ckGetMime(mime)

    ; Save the unwrapped MIME to a file:
    success = CkMime::ckSaveMime(mime,"unwrappedMime.txt")


    CkMime::ckDispose(mime)
    CkCert::ckDispose(signerCert)
    CkCert::ckDispose(decryptCert)


    ProcedureReturn
EndProcedure