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Create ECSDA Signature using Raw r and s Format (not ASN.1)

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Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

Zig

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

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

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

    // To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    // is signed.

    const sb = try chilkat.StringBuilder.init();
    defer sb.deinit();
    sb.append("The quick brown fox jumps over the lazy dog") catch {};
    const hash = try sb.getHash(alloc, "sha256", "base64", "utf-8");

    // Load the ECDSA key to be used for signing.
    const priv_key = try chilkat.PrivateKey.init();
    defer priv_key.deinit();
    priv_key.loadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem") catch {
        std.debug.print("{s}\n", .{try priv_key.getLastErrorText(alloc)});
        return;
    };

    const prng = try chilkat.Prng.init();
    defer prng.deinit();
    const ecdsa = try chilkat.Ecc.init();
    defer ecdsa.deinit();

    // Produce a signature that is not ASN.1, but is instead the concatenation
    // of the raw r and s signature parts.
    // This feature was added in Chilkat v9.5.0.97
    ecdsa.setAsnFormat(false);

    const ecdsa_sig_base64 = ecdsa.signHashENC(alloc, hash, "base64", priv_key, prng) catch {
        std.debug.print("{s}\n", .{try ecdsa.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("ECDSA signature = {s}\n", .{ecdsa_sig_base64});

    // -----------------------------------------------------------
    // Now let's verify the signature using the public key.

    const pub_key = try chilkat.PublicKey.init();
    defer pub_key.deinit();
    pub_key.loadFromFile("qa_data/ecc/secp256r1-pubkey.pem") catch {
        std.debug.print("{s}\n", .{try pub_key.getLastErrorText(alloc)});
        return;
    };

    // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    const result = ecdsa.verifyHashENC(hash, ecdsa_sig_base64, "base64", pub_key);
    if (result == 1) {
        std.debug.print("Signature is valid.\n", .{});
        return;
    }

    if (result == 0) {
        std.debug.print("Signature is invalid.\n", .{});
        return;
    }

    if (result < 0) {
        std.debug.print("{s}\n", .{try ecdsa.getLastErrorText(alloc)});
        std.debug.print("The VerifyHashENC method call failed.\n", .{});
        return;
    }
}