Fraud practiced on the surety by the creditor, will make the contract voidable, so fraud practiced on the surety by the principal debtor with the knowledge of the creditor will likewise avoid the contract,15 as concealment of the principal's fraud by the creditor, would amount to a fraud on the surety, and it would be a violation of the duty of good faith owing from the creditor to the surety, but if the principal debtor practices a fraud on the surety, of which the creditor has no knowledge even though this is the thing that induces the surety to make the contract, the surety will not on that account be released from liability to the creditor.16 The courts are particularly severe in enforcing the rule, on the creditor, in reference to his exercising good faith in informing the prospective surety of the true facts in connection with the contract, so far as they deem good faith requires him to inform the surety. Fraud, deceit or concealment, amounting to fraud, will avoid the contract.17