(C) RSA Signature/Verify with .key and .cer

See more RSA Examples

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

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

void ChilkatSample(void)
    {
    BOOL success;
    HCkPrivateKey privKey;
    HCkRsa rsa;
    const char *strData;
    const char *hexSig;
    HCkCert cert;
    HCkPublicKey pubKey;
    HCkRsa rsa2;

    success = FALSE;

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

    privKey = CkPrivateKey_Create();

    // Load the private key from an RSA .key file:
    success = CkPrivateKey_LoadPemFile(privKey,"privateKey.key");
    if (success == FALSE) {
        printf("%s\n",CkPrivateKey_lastErrorText(privKey));
        CkPrivateKey_Dispose(privKey);
        return;
    }

    rsa = CkRsa_Create();

    // Import the private key into the RSA component:
    success = CkRsa_UsePrivateKey(rsa,privKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        return;
    }

    // Create the signature as a hex string:
    CkRsa_putEncodingMode(rsa,"hex");

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

    // Sign the string using the sha256 hash algorithm.
    // Other valid choices are "md2", "sha1", "sha384",
    // "sha512", and "md5".
    hexSig = CkRsa_signStringENC(rsa,strData,"sha256");

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

    // Load a digital certificate from a .cer file:
    cert = CkCert_Create();

    success = CkCert_LoadFromFile(cert,"myCert.cer");
    if (success == FALSE) {
        printf("%s\n",CkCert_lastErrorText(cert));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        CkCert_Dispose(cert);
        return;
    }

    pubKey = CkPublicKey_Create();
    CkCert_GetPublicKey(cert,pubKey);

    // Now verify using a new instance of the RSA object:
    rsa2 = CkRsa_Create();

    // Import the public key into the RSA object:
    success = CkRsa_UsePublicKey(rsa2,pubKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa2));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        CkCert_Dispose(cert);
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa2);
        return;
    }

    // The signature is a hex string, so make sure the EncodingMode is correct:
    CkRsa_putEncodingMode(rsa2,"hex");

    // Verify the signature:
    success = CkRsa_VerifyStringENC(rsa2,strData,"sha256",hexSig);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa2));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        CkCert_Dispose(cert);
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa2);
        return;
    }

    printf("Success.\n");


    CkPrivateKey_Dispose(privKey);
    CkRsa_Dispose(rsa);
    CkCert_Dispose(cert);
    CkPublicKey_Dispose(pubKey);
    CkRsa_Dispose(rsa2);

    }