(Go) RSASSA-PSS Sign String to Create Base64 PCKS7 Signature

Signs a string to create a PKCS7 signature in the base64 encoding. The signature algorithm is RSASSA-PSS with SHA256.

Note: This example requires Chilkat v9.5.0.67 or greater.

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

    crypt := chilkat.NewCrypt2()

    // Get a digital certificate with private key from a .pfx
    // (Chilkat has many different ways to provide a cert + private key for siging.
    // Using a PFX is just one possible option.)
    pfx := chilkat.NewPfx()
    success := pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
    if success != true {
        fmt.Println(pfx.LastErrorText())
        crypt.DisposeCrypt2()
        pfx.DisposePfx()
        return
    }

    // Get the certificate to be used for signing.
    // (The typical case for a PFX is that it contains a cert with an associated private key,
    // as well as other certificates in the chain of authentication.  The cert with the private
    // key should be in the first position at index 0.)
    cert := pfx.GetCert(0)
    if pfx.LastMethodSuccess() != true {
        fmt.Println(pfx.LastErrorText())
        crypt.DisposeCrypt2()
        pfx.DisposePfx()
        return
    }

    crypt.SetSigningCert(cert)

    // Indicate that RSASSA-PSS with SHA256 should be used.
    crypt.SetSigningAlg("pss")
    crypt.SetHashAlgorithm("sha256")

    crypt.SetEncodingMode("base64")

    // Sign a string and return the base64 PKCS7 detached signature
    originalText := "This is a test"
    pkcs7sig := crypt.SignStringENC(originalText)
    fmt.Println("Detached Signature:")
    fmt.Println(*pkcs7sig)

    // This signature looks like this:
    // MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBgl .. YToLqEwTdU87ox5g7rvw==

    // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
    // then copy-and-paste the Base64 signature into the form and decode..

    // The signature can be verified against the original data like this:
    success = crypt.VerifyStringENC(originalText,*pkcs7sig)
    fmt.Println("Signature verified: ", success)
    success = crypt.VerifyStringENC("Not the original text",*pkcs7sig)
    fmt.Println("Signature verified: ", success)

    // Now we'll create an opaque signature (the opposite of a detached signature). 
    // An opaque signature is a PKCS7 message that contains both the original data and
    // the signature.  The verification process extracts the original data.
    opaqueSig := crypt.OpaqueSignStringENC(originalText)
    fmt.Println("Opaque Signature:")
    fmt.Println(*opaqueSig)

    // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
    // then copy-and-paste the Base64 signature into the form and decode..

    // We can verify and extract the original data:
    origTxt := crypt.OpaqueVerifyStringENC(*opaqueSig)
    if crypt.LastMethodSuccess() != true {
        fmt.Println("Signature verification failed.")
        fmt.Println(crypt.LastErrorText())
        cert.DisposeCert()
        crypt.DisposeCrypt2()
        pfx.DisposePfx()
        return
    }

    fmt.Println("Signature verified.")
    fmt.Println("Extracted text:", *origTxt)

    cert.DisposeCert()

    crypt.DisposeCrypt2()
    pfx.DisposePfx()