C++

Verify an RSA Signature Against the Signed Hash

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Demonstrates how to validate an RSA Signature against the hash that was signed. C++

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

void ChilkatSample(void)
    {
    bool success = false;

    CkBinData bd;
    int i;
    for (i = 0; i <= 100; i++) {
        bd.AppendEncoded("000102030405060708090A0B0C0D0E0F","hex");
    }

    const char *sha256_base64 = bd.getHash("sha256","base64");
    std::cout << "sha256 hash in base64 format: " << sha256_base64 << "\r\n";

    const char *base64_rsa_sig = "AwF2BbOvL6jA5DwmMAc9n6J2Cc8PI6Rj5W079+aKJcIEtPWRzHor0Bvc3aftGM3Jbgj6SXlIC3M3RYS7UZOnfiHKFNZgbxaNT5WwsWooK42ZkC8DBZl0p7OunBUKd5SciUo+TKilioeUkriN3L1Zl9hwi3HVDVqgVo3XXskwIftSqLSFlepTLTmOWj9Y93dp8J4D9RyLtNgFQBc0WB22tyJTsuY56mLcWe1AMF3LizB9OrbwjynF2u16xWlrJdugccz795fJBUV9aQSD+8S3KeqwQhoi8RK1uhD68aGCyaSpBq0NZ8COAkn7MXaF4POxrAAt8udfHM+PRfSOptcH/w==";

    //  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 hash against the signature.
    rsa.put_EncodingMode("base64");
    success = rsa.VerifyHashENC(sha256_base64,"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";
    }
    }