(Objective-C) Duplicate openssl dgst -sha256 -sign private.pem -out sha256.sig in.dat

Demonstrates how to duplicate this OpenSSL command:

openssl dgst -sha256 -sign private.pem -out sha256.sig in.dat

1. Creates a SHA256 digest of the contents of the input file
2. Signs the SHA256 digest using the private key.

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

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

CkoPrivateKey *pkey = [[CkoPrivateKey alloc] init];

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

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

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

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

// Load the file to be signed.
CkoBinData *bdFileData = [[CkoBinData alloc] init];
success = [bdFileData LoadFile: @"in.dat"];

CkoBinData *bdSig = [[CkoBinData alloc] init];
success = [rsa SignBd: bdFileData hashAlgorithm: @"sha256" bdSig: bdSig];
if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Save the binary signature to a file.
success = [bdSig WriteFile: @"signature.sig"];
if (success != YES) {
    NSLog(@"%@",@"Failed to write signature.sig.");
    return;
}

NSLog(@"%@",@"Success.");