Objective-C

ECDSA Sign Data and Verify Signature

See more ECC Examples

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

#import <CkoCrypt2.h>
#import <NSString.h>
#import <CkoPrivateKey.h>
#import <CkoPrng.h>
#import <CkoEcc.h>
#import <CkoPublicKey.h>

BOOL success = NO;

// 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];
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;
}