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A3/A4 Certificate to Create and Verify an Opaque PKCS7/CMS Signature

See more Digital Signatures Examples

Demonstrates how to use an A3 or A4 certificate w/ private key on a smartcard or token to create a PKCS7 opaque signature, and also how to verify an opaque signature.

An opaque signature is different than a detached PKCS7 signature in that it contains the original data. Verifying an opaque signature retrieves the original content.

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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    const crypt = try chilkat.Crypt2.init();
    defer crypt.deinit();

    // A certificate and private key is needed to create a signature.
    // Chilkat provides many different ways to load a certificate and private key, such
    // as from a smartcards and hardware tokens, PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
    // This example will load the default certificate from the smartcard that is currently in
    // the smartcard reader.

    const cert = try chilkat.Cert.init();
    defer cert.deinit();

    // If the smartcard or token requires a PIN, we can set it here to avoid the dialog...
    cert.setSmartCardPin("000000");

    cert.loadFromSmartcard("") catch {
        std.debug.print("{s}\n", .{try cert.getLastErrorText(alloc)});
        return;
    };

    // Tell it to use the cert and private key we've loaded.
    crypt.setSigningCert(cert) catch {
        std.debug.print("{s}\n", .{try crypt.getLastErrorText(alloc)});
        return;
    };

    // Indicate we want the opaque signature in base64 format:
    crypt.setEncodingMode("base64");

    // Sign the string using the "utf-8" byte representation:
    crypt.setCharset("utf-8");

    // Create the opaque signature:
    const original_data = "This is the string to be signed.";
    const opaque_sig = crypt.opaqueSignStringENC(alloc, original_data) catch {
        std.debug.print("{s}\n", .{try crypt.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("{s}\n", .{opaque_sig});

    // The output looks like this:
    // MIIPgQYJKoZIhvcNAQcCoIIPcjCCD24CAQExCzAJBgUrDgMCGgUAMC8GCSqGSIb3DQEHAaAiBCBUaGlzIGlzIHRoZSBzdHJpbmcgdG8gYmUgc...

    // ----------------------------------------------------------------------------------------------
    // Now let's verify the signature and retrieve the original data.
    // We'll use a new Crypt2 object to keep things completely separate...

    const v_crypt = try chilkat.Crypt2.init();
    defer v_crypt.deinit();

    // We only need the certificate to verify a signature (and extract the data from
    // an opaque signature).  The public key is always embedded within a certificate.
    v_crypt.setVerifyCert(cert) catch {
        std.debug.print("{s}\n", .{try v_crypt.getLastErrorText(alloc)});
        return;
    };

    v_crypt.setEncodingMode("base64");
    v_crypt.setCharset("utf-8");

    const extracted_data = v_crypt.opaqueVerifyStringENC(alloc, opaque_sig) catch {
        std.debug.print("{s}\n", .{try v_crypt.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("The extracted data: {s}\n", .{extracted_data});

    // The output is:
    // The extracted data: This is the string to be signed.
}