(Objective-C) Apple Keychain - Create RSA Signature

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Using an RSA private key stored in the Apple Keychain, create a signature by signing the SHA-256 hash of the provided string, then return the signature encoded in Base64 format.

Note: This example requires Chilkat v10.0.0 or greater.

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#import <CkoCert.h>
#import <CkoRsa.h>
#import <NSString.h>

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

CkoCert *cert = [[CkoCert alloc] init];

// On MacOS and iOS, the LoadByCommonName function will search the Apple Keychain for the matching certificate.

// A digital certificate's Common Name (CN) is a field in the certificate that specifies the name of the entity the 
// certificate is issued to. It is often used to identify the domain name, hostname, or organization the certificate represents. 

// For example:
// - In an SSL/TLS certificate for a website, the CN typically contains the domain name (e.g., "www.example.com").
// - For certificates representing individuals or organizations, the CN might include the person's name or the organization's name.

// The CN is part of the certificate's Subject field and is crucial for verifying that the certificate corresponds 
// to the intended entity, especially in SSL/TLS communications.

BOOL success = [cert LoadByCommonName: @"Example, Inc."];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

CkoRsa *rsa = [[CkoRsa alloc] init];
success = [rsa SetX509Cert: cert usePrivateKey: YES];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Generate an RSA signature by signing the SHA-256 hash of the provided string, 
// then return the signature encoded in Base64 format.
rsa.EncodingMode = @"base64";
NSString *sigBase64 = [rsa SignStringENC: @"to be signed" hashAlg: @"sha256"];
if (rsa.LastMethodSuccess == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

NSLog(@"%@",@"RSA Signature:");
NSLog(@"%@",sigBase64);