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. C++

#include <CkStringBuilder.h>
#include <CkPublicKey.h>
#include <CkRsa.h>

void ChilkatSample(void)
    {
    bool success = false;

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

    CkStringBuilder sb;
    bool crlfLineEnding = true;
    int i;
    for (i = 0; i <= 10; i++) {
        sb.AppendLine("This is a test.",crlfLineEnding);
    }

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

    //  Get the public key to be used for signature verification.
    CkPublicKey pubKey;
    success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem");
    if (success == false) {
        std::cout << pubKey.lastErrorText() << "\r\n";
        return;
    }

    CkRsa rsa;
    success = rsa.UsePublicKey(pubKey);
    if (success == false) {
        std::cout << rsa.lastErrorText() << "\r\n";
        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.
    rsa.put_Charset("utf-8");
    rsa.put_EncodingMode("base64");
    const char *signedString = sb.getAsString();
    success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig);

    if (success == false) {
        std::cout << rsa.lastErrorText() << "\r\n";
        std::cout << "Signature invalid." << "\r\n";
    }
    else {
        std::cout << "Signature valid." << "\r\n";
    }
    }