(C) Generate RSA Key and Sign a String

See more RSA Examples

Note: This example requires Chilkat v11.0.0 or greater.

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

void ChilkatSample(void)
    {
    BOOL success;
    HCkRsa rsa;
    HCkPrivateKey privKey;
    const char *strData;
    const char *hexSig;
    HCkPublicKey pubKey;

    success = FALSE;

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

    rsa = CkRsa_Create();

    // Generate a 2048-bit RSA key.
    privKey = CkPrivateKey_Create();
    success = CkRsa_GenKey(rsa,2048,privKey);

    CkRsa_UsePrivateKey(rsa,privKey);

    // Return the signature in hex.
    CkRsa_putEncodingMode(rsa,"hex");

    strData = "This is the string to be signed.";

    // Sign the SHA256 hash of the string.
    hexSig = CkRsa_signStringENC(rsa,strData,"sha256");

    printf("%s\n",hexSig);

    // Now verify the signature:
    pubKey = CkPublicKey_Create();
    CkPrivateKey_ToPublicKey(privKey,pubKey);
    CkRsa_UsePublicKey(rsa,pubKey);

    success = CkRsa_VerifyStringENC(rsa,strData,"sha256",hexSig);
    if (success == TRUE) {
        printf("Signature verified!\n");
    }
    else {
        printf("%s\n",CkRsa_lastErrorText(rsa));
    }

    // Try it with an invalid signature:
    success = CkRsa_VerifyStringENC(rsa,strData,"sha256","not a valid sig");
    if (success == TRUE) {
        printf("Signature verified!\n");
    }
    else {
        printf("Signature validation failed!\n");
    }

    // Try it with invalid data:
    success = CkRsa_VerifyStringENC(rsa,"Not the original data","sha256",hexSig);
    if (success == TRUE) {
        printf("Signature verified!\n");
    }
    else {
        printf("Signature validation failed!\n");
    }



    CkRsa_Dispose(rsa);
    CkPrivateKey_Dispose(privKey);
    CkPublicKey_Dispose(pubKey);

    }