While verifyiing the authenticity of cash at bank, the following things should be kept in under consideration.

1. Obtain a certificate from the bank confirming the balance at the close of the year as shown in the Pass Book.
2. Check the bank reconciliation statement.
3. Check the certificates in respect of fixed deposits or any type of deposits with banks.
4. Ensure that appropriate disclosure has been made in relation to balances/deposits with specific charge on them, or those held under the requirements of any law in the financial statements.
5. Remittances shown as being in transit should be examined with reference to their credit in the bank in the subsequent period. 
6. The auditor should examine that suitable adjustment are made in respect of cheques which have become stale as at the close of the year.
7. Where material amounts are held in bank accounts which are blocked due to any reason, the auditor should examine whether the relevant facts have been disclosed in the financial statements and
8. An auditor should satisfy himself with the genuineness of banking transactions and balances.