(Objective-C) Verify the RSA Signature of a SHA256 Hash

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Demonstrates how to verify an RSA signature of a SHA256 hash.

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

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

// Let's say you have a file containing the 32-bytes of a SHA256 hash,
// and a file that is an RSA signature of those 32 bytes.
// Here's how you verify using the RSA public key found in a PEM.

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
BOOL success = [pubKey LoadFromFile: @"rsaPubKey.pem"];
if (success == NO) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

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

// Get the public key.
success = [rsa ImportPublicKeyObj: pubKey];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Get the 32-byte SHA256 hash.
CkoBinData *bdHash = [[CkoBinData alloc] init];
success = [bdHash LoadFile: @"myHash.sha256"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load SHA256 hash.");
    return;
}

// Get the RSA signature to be validated.
CkoBinData *bdSig = [[CkoBinData alloc] init];
success = [bdSig LoadFile: @"mySig.sig"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load RSA signature.");
    return;
}

// Verify the signature against the SHA256 hash.
NSString *enc = @"base64";
rsa.EncodingMode = enc;
success = [rsa VerifyHashENC: [bdHash GetEncoded: enc] hashAlg: @"sha256" encodedSig: [bdSig GetEncoded: enc]];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

NSLog(@"%@",@"Signature validated.");