(Objective-C) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

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#import <CkoPublicKey.h>
#import <CkoStringBuilder.h>
#import <CkoJsonObject.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.

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

CkoStringBuilder *sbPem = [[CkoStringBuilder alloc] init];
BOOL bCrlf = YES;
[sbPem AppendLine: @"-----BEGIN PUBLIC KEY-----" crlf: bCrlf];
[sbPem AppendLine: @"MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF" crlf: bCrlf];
[sbPem AppendLine: @"3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA" crlf: bCrlf];
[sbPem AppendLine: @"04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s" crlf: bCrlf];
[sbPem AppendLine: @"Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF" crlf: bCrlf];
[sbPem AppendLine: @"wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE" crlf: bCrlf];
[sbPem AppendLine: @"f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W" crlf: bCrlf];
[sbPem AppendLine: @"SwIDAQAB" crlf: bCrlf];
[sbPem AppendLine: @"-----END PUBLIC KEY-----" crlf: bCrlf];

// Load the public key object from the PEM. 
BOOL success = [pubkey LoadFromString: [sbPem GetAsString]];
if (success != YES) {
    NSLog(@"%@",pubkey.LastErrorText);
    return;
}

// Build a small string to encrypt
CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json UpdateString: @"example" value: @"123"];
[json UpdateString: @"hello" value: @"world"];
NSLog(@"%@",[json Emit]);

// This is the JSON to be RSA encrypted:  {"example":"123","hello":"world"}

// IMPORTANT: RSA encryption is only used to encrypt small amounts of data.
// RSA is only able to encrypt data to a maximum amount of your key size (2048 bits = 256 bytes) 
// minus padding / header data (11 bytes for PKCS#1 v1.5 padding, 42 bytes for OAEP).
// As a result it is often not possible to encrypt files with RSA directly. 
// RSA is also not meant for this purpose. 
// 
// If you want to encrypt more data, you can use something like:
// 1) Generate a 256-bit random keystring K
// 2) Encrypt your data with AES-CBC with K
// 3) Encrypt K with RSA
// 4) Send both to the other side 

CkoRsa *rsa = [[CkoRsa alloc] init];
rsa.OaepPadding = YES;
rsa.OaepHash = @"SHA-256";
[rsa ImportPublicKeyObj: pubkey];
rsa.EncodingMode = @"base64";

// Note: The OAEP padding uses random bytes in the padding, and therefore each time encryption happens,
// even using the same data and key, the result will be different --  but still valid.  One should not expect
// to get the same output.
BOOL bUsePrivateKey = NO;
NSString *encryptedStr = [rsa EncryptStringENC: [json Emit] bUsePrivateKey: bUsePrivateKey];
if (rsa.LastMethodSuccess != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

NSLog(@"%@%@",@"Result: ",encryptedStr);