Unicode C

RSA-OAEP with SHA256 hashing

See more RSA Examples

RSA encrypt a SHA256 hash with OAEP padding. Unicode C

#include <C_CkPublicKeyW.h>
#include <C_CkStringBuilderW.h>
#include <C_CkJsonObjectW.h>
#include <C_CkRsaW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkPublicKeyW pubkey;
    HCkStringBuilderW sbPem;
    BOOL bCrlf;
    HCkJsonObjectW json;
    HCkRsaW rsa;
    BOOL bUsePrivateKey;
    const wchar_t *encryptedStr;

    success = FALSE;

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

    pubkey = CkPublicKeyW_Create();

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

    //  Load the public key object from the PEM. 
    success = CkPublicKeyW_LoadFromString(pubkey,CkStringBuilderW_getAsString(sbPem));
    if (success == FALSE) {
        wprintf(L"%s\n",CkPublicKeyW_lastErrorText(pubkey));
        CkPublicKeyW_Dispose(pubkey);
        CkStringBuilderW_Dispose(sbPem);
        return;
    }

    //  Build a small string to encrypt
    json = CkJsonObjectW_Create();
    CkJsonObjectW_UpdateString(json,L"example",L"123");
    CkJsonObjectW_UpdateString(json,L"hello",L"world");
    wprintf(L"%s\n",CkJsonObjectW_emit(json));

    //  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 

    rsa = CkRsaW_Create();
    CkRsaW_putPkcsPadding(rsa,FALSE);
    CkRsaW_putOaepHash(rsa,L"SHA-256");
    CkRsaW_UsePublicKey(rsa,pubkey);
    CkRsaW_putEncodingMode(rsa,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.
    bUsePrivateKey = FALSE;
    encryptedStr = CkRsaW_encryptStringENC(rsa,CkJsonObjectW_emit(json),bUsePrivateKey);
    if (CkRsaW_getLastMethodSuccess(rsa) == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        CkPublicKeyW_Dispose(pubkey);
        CkStringBuilderW_Dispose(sbPem);
        CkJsonObjectW_Dispose(json);
        CkRsaW_Dispose(rsa);
        return;
    }

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


    CkPublicKeyW_Dispose(pubkey);
    CkStringBuilderW_Dispose(sbPem);
    CkJsonObjectW_Dispose(json);
    CkRsaW_Dispose(rsa);

    }