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DSA Signature Create and Verify

See more DSA Examples

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

Zig

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

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

    var success: bool = false;

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

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

    crypt.setEncodingMode("hex");
    crypt.setHashAlgorithm("sha-1");

    // Return the SHA-1 hash of a file.  The file may be any size.
    // The Chilkat Crypt component will stream the file when
    // computing the hash, keeping the memory usage constant
    // and reasonable.
    // The 20-byte SHA-1 hash is returned as a hex-encoded string.
    const hash_str = try crypt.hashFileENC(alloc, "hamlet.xml");

    const dsa = try chilkat.Dsa.init();
    defer dsa.deinit();

    // Load a DSA private key from a PEM file.  Chilkat DSA
    // provides the ability to load and save DSA public and private
    // keys from encrypted or non-encrypted PEM or DER.
    // The LoadText method is for convenience only.  You may
    // use any means to load the contents of a PEM file into
    // a string.
    const pem_private_key = try dsa.loadText(alloc, "dsa_priv.pem");
    success = if (dsa.fromPem(pem_private_key)) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa.getLastErrorText(alloc)});
        return;
    }

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    success = dsa.verifyKey();
    if (!success) {
        std.debug.print("{s}\n", .{try dsa.getLastErrorText(alloc)});
        return;
    }

    // Load the hash to be signed into the DSA object:
    success = if (dsa.setEncodedHash("hex", hash_str)) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa.getLastErrorText(alloc)});
        return;
    }

    // Now that the DSA object contains both the private key and hash,
    // it is ready to create the signature:
    success = if (dsa.signHash()) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa.getLastErrorText(alloc)});
        return;
    }

    // If SignHash is successful, the DSA object contains the
    // signature.  It may be accessed as a hex or base64 encoded
    // string.  (It is also possible to access directly in byte array form via
    // the "Signature" property.)
    const hex_sig = try dsa.getEncodedSignature(alloc, "hex");
    std.debug.print("Signature:\n", .{});
    std.debug.print("{s}\n", .{hex_sig});

    // -----------------------------------------------------------
    // Step 2: Verify the DSA Signature
    // -----------------------------------------------------------

    const dsa2 = try chilkat.Dsa.init();
    defer dsa2.deinit();

    // Load the DSA public key to be used for verification:
    const pem_public_key = try dsa2.loadText(alloc, "dsa_pub.pem");
    success = if (dsa2.fromPublicPem(pem_public_key)) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa2.getLastErrorText(alloc)});
        return;
    }

    // Load the hash to be verified against the signature.
    success = if (dsa2.setEncodedHash("hex", hash_str)) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa2.getLastErrorText(alloc)});
        return;
    }

    // Load the signature:
    success = if (dsa2.setEncodedSignature("hex", hex_sig)) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa2.getLastErrorText(alloc)});
        return;
    }

    // Verify:
    success = if (dsa2.verify()) true else |_| false;
    if (!success) {
        std.debug.print("{s}\n", .{try dsa2.getLastErrorText(alloc)});
    } else {
        std.debug.print("DSA Signature Verified!\n", .{});
    }
}