(Objective-C) 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.

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#import <CkoStringBuilder.h>
#import <NSString.h>
#import <CkoPrivateKey.h>
#import <CkoPrng.h>
#import <CkoEcc.h>
#import <CkoPublicKey.h>

// 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.

CkoStringBuilder *sb = [[CkoStringBuilder alloc] init];
[sb Append: @"The quick brown fox jumps over the lazy dog"];
NSString *hash = [sb GetHash: @"sha256" encoding: @"base64" charset: @"utf-8"];

// Load the ECDSA key to be used for signing.
CkoPrivateKey *privKey = [[CkoPrivateKey alloc] init];
BOOL success = [privKey LoadPemFile: @"qa_data/ecc/secp256r1-key-pkcs8.pem"];
if (success != YES) {
    NSLog(@"%@",privKey.LastErrorText);
    return;
}

CkoPrng *prng = [[CkoPrng alloc] init];
CkoEcc *ecdsa = [[CkoEcc alloc] init];

// 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.AsnFormat = NO;

NSString *ecdsaSigBase64 = [ecdsa SignHashENC: hash encoding: @"base64" privkey: privKey prng: prng];
if (ecdsa.LastMethodSuccess != YES) {
    NSLog(@"%@",ecdsa.LastErrorText);
    return;
}

NSLog(@"%@%@",@"ECDSA signature = ",ecdsaSigBase64);

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

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
success = [pubKey LoadFromFile: @"qa_data/ecc/secp256r1-pubkey.pem"];
if (success != YES) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

// Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
int result = [[ecdsa VerifyHashENC: hash encodedSig: ecdsaSigBase64 encoding: @"base64" pubkey: pubKey] intValue];
if (result == 1) {
    NSLog(@"%@",@"Signature is valid.");
    return;
}

if (result == 0) {
    NSLog(@"%@",@"Signature is invalid.");
    return;
}

if (result < 0) {
    NSLog(@"%@",ecdsa.LastErrorText);
    NSLog(@"%@",@"The VerifyHashENC method call failed.");
    return;
}