(Objective-C) Duplicate openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

Demonstrates how to duplicate this OpenSSL command:

openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

1. Creates a SHA256 digest of the contents of the input file.
2. Verifies the SHA256 digest using the public key.

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#import <CkoPublicKey.h>
#import <CkoBinData.h>
#import <CkoRsa.h>

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

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];

// Load the public key from an PEM file:
BOOL success = [pubKey LoadFromFile: @"pubKey.pem"];
if (success != YES) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

// Load the data of the original file that was signed.
CkoBinData *bdFileData = [[CkoBinData alloc] init];
success = [bdFileData LoadFile: @"in.dat"];

// Load the signature.
CkoBinData *bdSig = [[CkoBinData alloc] init];
success = [bdSig LoadFile: @"signature.sig"];

CkoRsa *rsa = [[CkoRsa alloc] init];

// Import the public key into the RSA component:
success = [rsa ImportPublicKeyObj: pubKey];
if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// OpenSSL uses big-endian.
rsa.LittleEndian = NO;

success = [rsa VerifyBd: bdFileData hashAlgorithm: @"sha256" bdSig: bdSig];
if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    NSLog(@"%@",@"The signature was invalid.");
    return;
}

NSLog(@"%@",@"The signature was verified.");