(Unicode C++) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat C/C++ Library Downloads
MS Visual C/C++ Linux/CentOS C/C++ Alpine Linux C/C++ MAC OS X C/C++	armhf/aarch64 C/C++ C++ Builder iOS C/C++ Android C/C++	Solaris C/C++ MinGW C/C++

#include <CkPublicKeyW.h>
#include <CkStringBuilderW.h>
#include <CkJsonObjectW.h>
#include <CkRsaW.h>

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

    CkPublicKeyW pubkey;

    CkStringBuilderW sbPem;
    bool bCrlf = true;
    sbPem.AppendLine(L"-----BEGIN PUBLIC KEY-----",bCrlf);
    sbPem.AppendLine(L"MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF",bCrlf);
    sbPem.AppendLine(L"3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA",bCrlf);
    sbPem.AppendLine(L"04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s",bCrlf);
    sbPem.AppendLine(L"Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF",bCrlf);
    sbPem.AppendLine(L"wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE",bCrlf);
    sbPem.AppendLine(L"f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W",bCrlf);
    sbPem.AppendLine(L"SwIDAQAB",bCrlf);
    sbPem.AppendLine(L"-----END PUBLIC KEY-----",bCrlf);

    // Load the public key object from the PEM. 
    bool success = pubkey.LoadFromString(sbPem.getAsString());
    if (success != true) {
        wprintf(L"%s\n",pubkey.lastErrorText());
        return;
    }

    // Build a small string to encrypt
    CkJsonObjectW json;
    json.UpdateString(L"example",L"123");
    json.UpdateString(L"hello",L"world");
    wprintf(L"%s\n",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 

    CkRsaW rsa;
    rsa.put_OaepPadding(true);
    rsa.put_OaepHash(L"SHA-256");
    rsa.ImportPublicKeyObj(pubkey);
    rsa.put_EncodingMode(L"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 = false;
    const wchar_t *encryptedStr = rsa.encryptStringENC(json.emit(),bUsePrivateKey);
    if (rsa.get_LastMethodSuccess() != true) {
        wprintf(L"%s\n",rsa.lastErrorText());
        return;
    }

    wprintf(L"Result: %s\n",encryptedStr);
    }