(Visual FoxPro) Extract PKCS7 Signature Digest

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loCrypt
LOCAL lcP7mFile
LOCAL lcOutPath
LOCAL lnVerified
LOCAL loPkcs7Data
LOCAL loSbBase64
LOCAL lcHexStr
LOCAL lnBHaveBase64
LOCAL i
LOCAL lcDigest

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt = CreateObject('Chilkat.Crypt2')

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.
lnVerified = loCrypt.VerifyP7M(lcP7mFile,lcOutPath)
IF (lnVerified <> 1) THEN
    ? loCrypt.LastErrorText
    RELEASE loCrypt
    CANCEL
ENDIF

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

* Load the .p7m into memory...
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.BinData')
loPkcs7Data = CreateObject('Chilkat.BinData')
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.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbBase64 = CreateObject('Chilkat.StringBuilder')
lcHexStr = loPkcs7Data.GetEncodedChunk(0,2,"hex")
loSbBase64.Append(lcHexStr)

lnBHaveBase64 = 0
IF (loSbBase64.ContentsEqual("4D49",1) = 1) THEN
    lnBHaveBase64 = 1
    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 (lnBHaveBase64) THEN
        lcDigest = loCrypt.Pkcs7ExtractDigest(i,loSbBase64.GetAsString())
    ELSE
        lcDigest = loCrypt.Pkcs7ExtractDigest(i,loPkcs7Data.GetEncoded("base64"))
    ENDIF

    IF (loCrypt.LastMethodSuccess <> 1) THEN
        ? loCrypt.LastErrorText
        RELEASE loCrypt
        RELEASE loPkcs7Data
        RELEASE loSbBase64
        CANCEL
    ENDIF

    ? "Signer " + STR(i + 1) + " digest = " + lcDigest
    i = i + 1
ENDDO

RELEASE loCrypt
RELEASE loPkcs7Data
RELEASE loSbBase64