(PureBasic) Extract PKCS7 Signature Digest

Demonstrates how to extract a signature digest from a PKCS7 signature.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkBinData.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkCrypt2.pb"

Procedure ChilkatExample()

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

    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    p7mFile.s = "qa_data/p7m/test.pdf.p7m"
    outPath.s = "qa_output/test.pdf"

    ; First let's see if this .p7m signature can be verified, and the original file extracted.
    verified.i = CkCrypt2::ckVerifyP7M(crypt,p7mFile,outPath)
    If verified <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        ProcedureReturn
    EndIf

    ; How many signers?
    ; (The NumSignerCerts property is set whenever a signature is verified.)
    Debug "Num Signers: " + Str(CkCrypt2::ckNumSignerCerts(crypt))

    ; Load the .p7m into memory...
    pkcs7Data.i = CkBinData::ckCreate()
    If pkcs7Data.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkBinData::ckLoadFile(pkcs7Data,p7mFile)

    ; Check to see if this .p7m contains the binary bytes, or if it's
    ; already base64 encoded.  Get the 1st two bytes.  If the first two 
    ; bytes are the us-ascii values "MI", then we have base64.
    sbBase64.i = CkStringBuilder::ckCreate()
    If sbBase64.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    hexStr.s = CkBinData::ckGetEncodedChunk(pkcs7Data,0,2,"hex")
    CkStringBuilder::ckAppend(sbBase64,hexStr)

    bHaveBase64.i = 0
    If CkStringBuilder::ckContentsEqual(sbBase64,"4D49",1) = 1
        bHaveBase64 = 1
        CkStringBuilder::ckClear(sbBase64)
        CkStringBuilder::ckAppendBd(sbBase64,pkcs7Data,"utf-8",0,0)
    EndIf

    ; Get each signer's signature digest.
    CkCrypt2::setCkEncodingMode(crypt, "base64")
    i.i = 0
    digest.s
    While i < CkCrypt2::ckNumSignerCerts(crypt)
        If bHaveBase64
            digest = CkCrypt2::ckPkcs7ExtractDigest(crypt,i,CkStringBuilder::ckGetAsString(sbBase64))
        Else
            digest = CkCrypt2::ckPkcs7ExtractDigest(crypt,i,CkBinData::ckGetEncoded(pkcs7Data,"base64"))
        EndIf

        If CkCrypt2::ckLastMethodSuccess(crypt) <> 1
            Debug CkCrypt2::ckLastErrorText(crypt)
            CkCrypt2::ckDispose(crypt)
            CkBinData::ckDispose(pkcs7Data)
            CkStringBuilder::ckDispose(sbBase64)
            ProcedureReturn
        EndIf

        Debug "Signer " + Str(i + 1) + " digest = " + digest
        i = i + 1
    Wend


    CkCrypt2::ckDispose(crypt)
    CkBinData::ckDispose(pkcs7Data)
    CkStringBuilder::ckDispose(sbBase64)


    ProcedureReturn
EndProcedure