How to validate Android Receipt.

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I implemented openIAB successfully, now i want to validate the receipt. The only thing OpenIAB provide me about my transaction is using purchase.originalJson.
which is look like this.
{"packageName":"com.test.jellysmasher","orderId":"transactionId.android.test.purchased","productId":"android.test.purchased","developerPayload":"","purchaseTime":0,"purchaseState":0,"purchaseToken":"inapp:com.test.jellysmasher:android.test.purchased"}

1: Can we test validation using android.test.purchase
2: How can I get signature for this.
3: what is public 64 key for this

Above questions are being asked by my web developer
please please help its urgent i am already behind my deadline