Unicode C

Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed. Unicode C

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

void ChilkatSample(void)
    {
    BOOL success;
    HCkStringBuilderW sb;
    BOOL crlfLineEnding;
    int i;
    const wchar_t *base64_rsa_sig;
    HCkPublicKeyW pubKey;
    HCkRsaW rsa;
    const wchar_t *signedString;

    success = FALSE;

    //  Create the same string we previously signed in this example: 
    //  RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

    sb = CkStringBuilderW_Create();
    crlfLineEnding = TRUE;

    for (i = 0; i <= 10; i++) {
        CkStringBuilderW_AppendLine(sb,L"This is a test.",crlfLineEnding);
    }

    base64_rsa_sig = L"gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ==";

    //  Get the public key to be used for signature verification.
    pubKey = CkPublicKeyW_Create();
    success = CkPublicKeyW_LoadFromFile(pubKey,L"rsaKeys/chilkat-rsa-2048.pem");
    if (success == FALSE) {
        wprintf(L"%s\n",CkPublicKeyW_lastErrorText(pubKey));
        CkStringBuilderW_Dispose(sb);
        CkPublicKeyW_Dispose(pubKey);
        return;
    }

    rsa = CkRsaW_Create();
    success = CkRsaW_UsePublicKey(rsa,pubKey);
    if (success == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        CkStringBuilderW_Dispose(sb);
        CkPublicKeyW_Dispose(pubKey);
        CkRsaW_Dispose(rsa);
        return;
    }

    //  Verify the string against the signature.
    //  We signed the utf-8 byte representation of the string, so we must indicate
    //  to also validate against the utf-8 byte representation.
    CkRsaW_putCharset(rsa,L"utf-8");
    CkRsaW_putEncodingMode(rsa,L"base64");
    signedString = CkStringBuilderW_getAsString(sb);
    success = CkRsaW_VerifyStringENC(rsa,signedString,L"sha256",base64_rsa_sig);

    if (success == FALSE) {
        wprintf(L"%s\n",CkRsaW_lastErrorText(rsa));
        wprintf(L"Signature invalid.\n");
    }
    else {
        wprintf(L"Signature valid.\n");
    }



    CkStringBuilderW_Dispose(sb);
    CkPublicKeyW_Dispose(pubKey);
    CkRsaW_Dispose(rsa);

    }