(Go) Extract PKCS7 Signature Digest

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

Chilkat Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

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

    crypt := chilkat.NewCrypt2()

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

    // First let's see if this .p7m signature can be verified, and the original file extracted.
    verified := crypt.VerifyP7M(p7mFile,outPath)
    if verified != true {
        fmt.Println(crypt.LastErrorText())
        return
    }

    // How many signers?
    // (The NumSignerCerts property is set whenever a signature is verified.)
    fmt.Println("Num Signers: ", crypt.NumSignerCerts())

    // Load the .p7m into memory...
    pkcs7Data := chilkat.NewBinData()
    pkcs7Data.LoadFile(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 := chilkat.NewStringBuilder()
    hexStr := pkcs7Data.GetEncodedChunk(0,2,"hex")
    sbBase64.Append(*hexStr)

    bHaveBase64 := false
    if sbBase64.ContentsEqual("4D49",true) == true {
        bHaveBase64 = true
        sbBase64.Clear()
        sbBase64.AppendBd(pkcs7Data,"utf-8",0,0)
    }

    // Get each signer's signature digest.
    crypt.SetEncodingMode("base64")
    i := 0
    var digest *string = new(string)
    for i < crypt.NumSignerCerts() {
        if bHaveBase64 {
            digest = crypt.Pkcs7ExtractDigest(i,*sbBase64.GetAsString())
        }
        else {
            digest = crypt.Pkcs7ExtractDigest(i,*pkcs7Data.GetEncoded("base64"))
        }

        if crypt.LastMethodSuccess() != true {
            fmt.Println(crypt.LastErrorText())
            return
        }

        fmt.Println("Signer ", i + 1, " digest = ", *digest)
        i = i + 1
    }