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 <C_CkBinData.h>
#include <C_CkPublicKey.h>
#include <C_CkRsa.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkBinData bd;
    int i;
    const char *sha256_base64;
    const char *base64_rsa_sig;
    HCkPublicKey pubKey;
    HCkRsa rsa;

    success = FALSE;

    bd = CkBinData_Create();

    for (i = 0; i <= 100; i++) {
        CkBinData_AppendEncoded(bd,"000102030405060708090A0B0C0D0E0F","hex");
    }

    sha256_base64 = CkBinData_getHash(bd,"sha256","base64");
    printf("sha256 hash in base64 format: %s\n",sha256_base64);

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

    //  Get the public key to be used for signature verification.
    pubKey = CkPublicKey_Create();
    success = CkPublicKey_LoadFromFile(pubKey,"rsaKeys/chilkat-rsa-2048.pem");
    if (success == FALSE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubKey));
        CkBinData_Dispose(bd);
        CkPublicKey_Dispose(pubKey);
        return;
    }

    rsa = CkRsa_Create();
    success = CkRsa_UsePublicKey(rsa,pubKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkBinData_Dispose(bd);
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa);
        return;
    }

    //  Verify the hash against the signature.
    CkRsa_putEncodingMode(rsa,"base64");
    success = CkRsa_VerifyHashENC(rsa,sha256_base64,"sha256",base64_rsa_sig);

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



    CkBinData_Dispose(bd);
    CkPublicKey_Dispose(pubKey);
    CkRsa_Dispose(rsa);

    }