(Objective-C) ECDSA Sign Data and Verify Signature

Demonstrates using the Elliptic Curve Digital Signature Algorithm to hash data and sign it. Also demonstrates how to verify the ECDSA signature.

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#import <CkoCrypt2.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.

// Use Chilkat Crypt2 to generate a hash for any of the following
// hash algorithms: SHA256, SHA384, SHA512, SHA1, MD5, MD2, HAVAL, RIPEMD128/160/256/320

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];
crypt.HashAlgorithm = @"SHA256";
crypt.Charset = @"utf-8";
crypt.EncodingMode = @"base64";

// Hash a string.
NSString *hash1 = [crypt HashStringENC: @"The quick brown fox jumps over the lazy dog"];
NSLog(@"%@%@",@"hash1 = ",hash1);

// Or hash a file..
NSString *hash2 = [crypt HashFileENC: @"qa_data/hamlet.xml"];
NSLog(@"%@%@",@"hash2 = ",hash2);

// (The Crypt2 API provides many other ways to hash data..)

// -----------------------------------------------------------
// An ECDSA private key is used for signing.  The public key is for signature verification.
// Load our ECC private key.
// Our private key file contains this:

// 	// -----BEGIN PRIVATE KEY-----
// 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
// 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
// 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
// 	-----END PRIVATE KEY-----

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

// We'll need a PRNG source for random number generation.
// Use Chilkat's PRNG (for the Fortuna PRNG algorithm).
CkoPrng *prng = [[CkoPrng alloc] init];

// Sign the hash..
CkoEcc *ecdsa = [[CkoEcc alloc] init];
NSString *ecdsaSigBase64 = [ecdsa SignHashENC: hash1 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;
}

int result = [[ecdsa VerifyHashENC: hash1 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;
}