(Lianja) Extract PKCS7 Signature Digest

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

Chilkat Lianja Extension Download Chilkat Lianja Extension

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

loCrypt = createobject("CkCrypt2")

lcP7mFile = "qa_data/p7m/test.pdf.p7m"
lcOutPath = "qa_output/test.pdf"

// First let's see if this .p7m signature can be verified, and the original file extracted.
llVerified = loCrypt.VerifyP7M(lcP7mFile,lcOutPath)
if (llVerified <> .T.) then
    ? loCrypt.LastErrorText
    release loCrypt
    return
endif

// How many signers?
// (The NumSignerCerts property is set whenever a signature is verified.)
? "Num Signers: " + str(loCrypt.NumSignerCerts)

// Load the .p7m into memory...
loPkcs7Data = createobject("CkBinData")
loPkcs7Data.LoadFile(lcP7mFile)

// 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.
loSbBase64 = createobject("CkStringBuilder")
lcHexStr = loPkcs7Data.GetEncodedChunk(0,2,"hex")
loSbBase64.Append(lcHexStr)

llBHaveBase64 = .F.
if (loSbBase64.ContentsEqual("4D49",.T.) = .T.) then
    llBHaveBase64 = .T.
    loSbBase64.Clear()
    loSbBase64.AppendBd(loPkcs7Data,"utf-8",0,0)
endif

// Get each signer's signature digest.
loCrypt.EncodingMode = "base64"
i = 0

do while i < loCrypt.NumSignerCerts
    if (llBHaveBase64) then
        lcDigest = loCrypt.Pkcs7ExtractDigest(i,loSbBase64.GetAsString())
    else
        lcDigest = loCrypt.Pkcs7ExtractDigest(i,loPkcs7Data.GetEncoded("base64"))
    endif

    if (loCrypt.LastMethodSuccess <> .T.) then
        ? loCrypt.LastErrorText
        release loCrypt
        release loPkcs7Data
        release loSbBase64
        return
    endif

    ? "Signer " + str(i + 1) + " digest = " + lcDigest
    i = i + 1
enddo


release loCrypt
release loPkcs7Data
release loSbBase64