(C) RSASSA-PSS Sign String to Create Base64 PCKS7 Signature

Signs a string to create a PKCS7 signature in the base64 encoding. The signature algorithm is RSASSA-PSS with SHA256.

Note: This example requires Chilkat v9.5.0.67 or greater.

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#include <C_CkCrypt2.h>
#include <C_CkPfx.h>
#include <C_CkCert.h>

void ChilkatSample(void)
    {
    HCkCrypt2 crypt;
    HCkPfx pfx;
    BOOL success;
    HCkCert cert;
    const char *originalText;
    const char *pkcs7sig;
    const char *opaqueSig;
    const char *origTxt;

    // This example requires the Chilkat Crypt API to have been previously unlocked.
    // See Unlock Chilkat Crypt for sample code.

    crypt = CkCrypt2_Create();

    // Get a digital certificate with private key from a .pfx
    // (Chilkat has many different ways to provide a cert + private key for siging.
    // Using a PFX is just one possible option.)
    pfx = CkPfx_Create();
    success = CkPfx_LoadPfxFile(pfx,"qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD");
    if (success != TRUE) {
        printf("%s\n",CkPfx_lastErrorText(pfx));
        CkCrypt2_Dispose(crypt);
        CkPfx_Dispose(pfx);
        return;
    }

    // Get the certificate to be used for signing.
    // (The typical case for a PFX is that it contains a cert with an associated private key,
    // as well as other certificates in the chain of authentication.  The cert with the private
    // key should be in the first position at index 0.)
    cert = CkPfx_GetCert(pfx,0);
    if (CkPfx_getLastMethodSuccess(pfx) != TRUE) {
        printf("%s\n",CkPfx_lastErrorText(pfx));
        CkCrypt2_Dispose(crypt);
        CkPfx_Dispose(pfx);
        return;
    }

    CkCrypt2_SetSigningCert(crypt,cert);

    // Indicate that RSASSA-PSS with SHA256 should be used.
    CkCrypt2_putSigningAlg(crypt,"pss");
    CkCrypt2_putHashAlgorithm(crypt,"sha256");

    CkCrypt2_putEncodingMode(crypt,"base64");

    // Sign a string and return the base64 PKCS7 detached signature
    originalText = "This is a test";
    pkcs7sig = CkCrypt2_signStringENC(crypt,originalText);
    printf("Detached Signature:\n");
    printf("%s\n",pkcs7sig);

    // This signature looks like this:
    // MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBgl .. YToLqEwTdU87ox5g7rvw==

    // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
    // then copy-and-paste the Base64 signature into the form and decode..

    // The signature can be verified against the original data like this:
    success = CkCrypt2_VerifyStringENC(crypt,originalText,pkcs7sig);
    printf("Signature verified: %d\n",success);
    success = CkCrypt2_VerifyStringENC(crypt,"Not the original text",pkcs7sig);
    printf("Signature verified: %d\n",success);

    // Now we'll create an opaque signature (the opposite of a detached signature). 
    // An opaque signature is a PKCS7 message that contains both the original data and
    // the signature.  The verification process extracts the original data.
    opaqueSig = CkCrypt2_opaqueSignStringENC(crypt,originalText);
    printf("Opaque Signature:\n");
    printf("%s\n",opaqueSig);

    // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
    // then copy-and-paste the Base64 signature into the form and decode..

    // We can verify and extract the original data:
    origTxt = CkCrypt2_opaqueVerifyStringENC(crypt,opaqueSig);
    if (CkCrypt2_getLastMethodSuccess(crypt) != TRUE) {
        printf("Signature verification failed.\n");
        printf("%s\n",CkCrypt2_lastErrorText(crypt));
        CkCert_Dispose(cert);
        CkCrypt2_Dispose(crypt);
        CkPfx_Dispose(pfx);
        return;
    }

    printf("Signature verified.\n");
    printf("Extracted text:%s\n",origTxt);

    CkCert_Dispose(cert);


    CkCrypt2_Dispose(crypt);
    CkPfx_Dispose(pfx);

    }