Suppose Bob wishes to send a message m to Alice. He knows N and e, which Alice has announced. He turns m into a number n < N, using some previously agreed-upon reversible protocol. For example, each character in a plaintext message could be converted to its ASCII code, and the codes concatenated into a single number. If necessary, he can break m into pieces and encrypt each piece separately. He then computes the ciphertext c:

This can be done quickly using the method of exponentiation by squaring. Bob then transmits c to Alice.