In the Embassies area of the Citadel, I talked to an officer named Delk. He's requesting I find some Cerberus ciphers for him. The specific quest text is as follows:

A C-Sec officer needs updated ciphers to break Cerberus codes. Find the ciphers and deliver them to him, at the Citadel embassy.

Where are the ciphers, and what is the reward for returning them to Delk?

2 Answers

From this walkthrough:

You will have to wait until you unlock the N7: Communication Hub mission after the Priority: Perseus Veil main story mission. In the Communication Hub mission, search a console marked with codes to find the cipher and return it to the C-Sec officer. As you so often can, you may also purchase the codes from the Spectre console on the Citadel if you miss them during the mission.

And from here:

Reward

Experience, Credits, War Asset Update

That latter site has a decent walkthrough for the N7: Communication Hub mission as well, if you need it.

1

If you miss them on your mission you can buy them along with other side quest items at the procurement computer in the docking bay or at your personal computer on the citadel in the specter room