(C) Create a JWS Using ECDSA P-256 SHA-256

Creates and validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v9.5.0.66 or greater.

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#include <C_CkStringBuilder.h>
#include <C_CkPrivateKey.h>
#include <C_CkJsonObject.h>
#include <C_CkJws.h>
#include <C_CkPublicKey.h>

void ChilkatSample(void)
    {
    HCkStringBuilder sbJwk;
    HCkPrivateKey eccKey;
    BOOL success;
    HCkJsonObject jwsProtHdr;
    HCkJws jws;
    int signatureIndex;
    BOOL bIncludeBom;
    const char *payloadStr;
    const char *jwsCompact;
    HCkJws jws2;
    HCkPublicKey eccPubKey;
    int v;
    HCkJsonObject joseHeader;

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

    // Note: This example requires Chilkat v9.5.0.66 or greater.

    // Use the following ECC key loaded from JWK format.
    sbJwk = CkStringBuilder_Create();
    CkStringBuilder_Append(sbJwk,"{\"kty\":\"EC\",");
    CkStringBuilder_Append(sbJwk,"\"crv\":\"P-256\",");
    CkStringBuilder_Append(sbJwk,"\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\",");
    CkStringBuilder_Append(sbJwk,"\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\",");
    CkStringBuilder_Append(sbJwk,"\"d\":\"jpsQnnGQmL-YBIffH1136cspYG6-0iY7X1fCE9-E9LI\"");
    CkStringBuilder_Append(sbJwk,"}");

    eccKey = CkPrivateKey_Create();
    // Note: This example loads the ECDSA key from JWK format.  Any format can be loaded
    // into the private key object. (See the online reference documentation..)
    success = CkPrivateKey_LoadJwk(eccKey,CkStringBuilder_getAsString(sbJwk));
    if (success != TRUE) {
        printf("%s\n",CkPrivateKey_lastErrorText(eccKey));
        CkStringBuilder_Dispose(sbJwk);
        CkPrivateKey_Dispose(eccKey);
        return;
    }

    // Create the JWS Protected Header
    jwsProtHdr = CkJsonObject_Create();
    CkJsonObject_AppendString(jwsProtHdr,"alg","ES256");

    jws = CkJws_Create();

    // Set the protected header:
    signatureIndex = 0;
    CkJws_SetProtectedHeader(jws,signatureIndex,jwsProtHdr);

    // Set the ECC key:
    CkJws_SetPrivateKey(jws,signatureIndex,eccKey);

    // Set the payload.
    bIncludeBom = FALSE;
    payloadStr = "In our village, folks say God crumbles up the old moon into stars.";
    CkJws_SetPayload(jws,payloadStr,"utf-8",bIncludeBom);

    // Create the JWS
    // By default, the compact serialization is used.
    jwsCompact = CkJws_createJws(jws);
    if (CkJws_getLastMethodSuccess(jws) != TRUE) {
        printf("%s\n",CkJws_lastErrorText(jws));
        CkStringBuilder_Dispose(sbJwk);
        CkPrivateKey_Dispose(eccKey);
        CkJsonObject_Dispose(jwsProtHdr);
        CkJws_Dispose(jws);
        return;
    }

    printf("JWS: %s\n",jwsCompact);

    // Note: ECC signatures use random values, so the output will be different each time a signature is produced.
    // sample output:
    // JWS: eyJhbGciOiJFUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.J6EGTNkeuEjehHHBu0SOKzifm8r35wbx49A5964pxzB7gannyZZPMkK7vmlaPJ-K8Xmm8cZsQySAPC12Xd8avw

    // Now load the JWS, validate, and recover the original text.
    jws2 = CkJws_Create();

    // Load the JWS.
    success = CkJws_LoadJws(jws2,jwsCompact);

    eccPubKey = CkPrivateKey_GetPublicKey(eccKey);

    // Set the ECC public key used for validation.
    signatureIndex = 0;
    CkJws_SetPublicKey(jws2,signatureIndex,eccPubKey);
    CkPublicKey_Dispose(eccPubKey);

    // Validate the 1st (and only) signature at index 0..
    v = CkJws_Validate(jws2,signatureIndex);
    if (v < 0) {
        // Perhaps Chilkat was not unlocked or the trial expired..
        printf("Method call failed for some other reason.\n");
        printf("%s\n",CkJws_lastErrorText(jws2));
        CkStringBuilder_Dispose(sbJwk);
        CkPrivateKey_Dispose(eccKey);
        CkJsonObject_Dispose(jwsProtHdr);
        CkJws_Dispose(jws);
        CkJws_Dispose(jws2);
        return;
    }

    if (v == 0) {
        printf("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.\n");
        CkStringBuilder_Dispose(sbJwk);
        CkPrivateKey_Dispose(eccKey);
        CkJsonObject_Dispose(jwsProtHdr);
        CkJws_Dispose(jws);
        CkJws_Dispose(jws2);
        return;
    }

    // If we get here, the signature was validated..
    printf("Signature validated.\n");

    // Recover the original content:
    printf("%s\n",CkJws_getPayload(jws2,"utf-8"));

    // Examine the protected header:
    joseHeader = CkJws_GetProtectedHeader(jws2,signatureIndex);
    if (CkJws_getLastMethodSuccess(jws2) != TRUE) {
        printf("No protected header found at the given index.\n");
        CkStringBuilder_Dispose(sbJwk);
        CkPrivateKey_Dispose(eccKey);
        CkJsonObject_Dispose(jwsProtHdr);
        CkJws_Dispose(jws);
        CkJws_Dispose(jws2);
        return;
    }

    CkJsonObject_putEmitCompact(joseHeader,FALSE);

    printf("Protected (JOSE) header:\n");
    printf("%s\n",CkJsonObject_emit(joseHeader));
    CkJsonObject_Dispose(joseHeader);

    // Output:

    // Signature validated.
    // In our village, folks say God crumbles up the old moon into stars.
    // Protected (JOSE) header:
    // { 
    //   "alg": "ES256"
    // }


    CkStringBuilder_Dispose(sbJwk);
    CkPrivateKey_Dispose(eccKey);
    CkJsonObject_Dispose(jwsProtHdr);
    CkJws_Dispose(jws);
    CkJws_Dispose(jws2);

    }