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

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_CkPublicKey.h>
#include <C_CkJws.h>
#include <C_CkJsonObject.h>

void ChilkatSample(void)
    {
    HCkStringBuilder sbPubKey;
    HCkPublicKey pubKey;
    BOOL success;
    HCkJws jws;
    int signatureIndex;
    HCkStringBuilder sbJws;
    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.

    // This example takes a JSON signature in compact serialization format,
    // and uses an ECDSA public key to validate and recover the protected header and payload.

    // We only need a public key for signature validation.  This is the ECDSA public key
    // that is used:

    //      {"kty":"EC", 
    //       "crv":"P-256", 
    //       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
    //       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
    //      } 

    sbPubKey = CkStringBuilder_Create();
    CkStringBuilder_Append(sbPubKey,"{\"kty\":\"EC\",");
    CkStringBuilder_Append(sbPubKey,"\"crv\":\"P-256\",");
    CkStringBuilder_Append(sbPubKey,"\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\",");
    CkStringBuilder_Append(sbPubKey,"\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\"");
    CkStringBuilder_Append(sbPubKey,"}");

    pubKey = CkPublicKey_Create();
    success = CkPublicKey_LoadFromString(pubKey,CkStringBuilder_getAsString(sbPubKey));
    if (success != TRUE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubKey));
        CkStringBuilder_Dispose(sbPubKey);
        CkPublicKey_Dispose(pubKey);
        return;
    }

    jws = CkJws_Create();

    // Set the ECC public key:
    signatureIndex = 0;
    CkJws_SetPublicKey(jws,signatureIndex,pubKey);

    // Load the JWS.
    sbJws = CkStringBuilder_Create();
    CkStringBuilder_Append(sbJws,"eyJhbGciOiJFUzI1NiJ9");
    CkStringBuilder_Append(sbJws,".");
    CkStringBuilder_Append(sbJws,"eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt");
    CkStringBuilder_Append(sbJws,"cGxlLmNvbS9pc19yb290Ijp0cnVlfQ");
    CkStringBuilder_Append(sbJws,".");
    CkStringBuilder_Append(sbJws,"DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA");
    CkStringBuilder_Append(sbJws,"pmWQxfKTUJqPP3-Kg6NU1Q");

    success = CkJws_LoadJwsSb(jws,sbJws);
    if (success != TRUE) {
        printf("%s\n",CkJws_lastErrorText(jws));
        CkStringBuilder_Dispose(sbPubKey);
        CkPublicKey_Dispose(pubKey);
        CkJws_Dispose(jws);
        CkStringBuilder_Dispose(sbJws);
        return;
    }

    // Validate the 1st (and only) signature at index 0..
    v = CkJws_Validate(jws,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(jws));
        CkStringBuilder_Dispose(sbPubKey);
        CkPublicKey_Dispose(pubKey);
        CkJws_Dispose(jws);
        CkStringBuilder_Dispose(sbJws);
        return;
    }

    if (v == 0) {
        printf("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.\n");
        CkStringBuilder_Dispose(sbPubKey);
        CkPublicKey_Dispose(pubKey);
        CkJws_Dispose(jws);
        CkStringBuilder_Dispose(sbJws);
        return;
    }

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

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

    // Examine the protected header:
    joseHeader = CkJws_GetProtectedHeader(jws,signatureIndex);
    if (CkJws_getLastMethodSuccess(jws) != TRUE) {
        printf("No protected header found at the given index.\n");
        CkStringBuilder_Dispose(sbPubKey);
        CkPublicKey_Dispose(pubKey);
        CkJws_Dispose(jws);
        CkStringBuilder_Dispose(sbJws);
        return;
    }

    CkJsonObject_putEmitCompact(joseHeader,FALSE);

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

    // Output:

    // 	Signature validated.
    // 	--
    // 	Recovered content:
    // 	{"iss":"joe",
    // 	 "exp":1300819380,
    // 	 "http://example.com/is_root":true}
    // 	--
    // 	Protected (JOSE) header:
    // 	{ 
    // 	  "alg": "ES256"
    // 	}


    CkStringBuilder_Dispose(sbPubKey);
    CkPublicKey_Dispose(pubKey);
    CkJws_Dispose(jws);
    CkStringBuilder_Dispose(sbJws);

    }