As I read through the Harry Potter series, I am bothered by the apparent dearth of secure ways to transmit information. I would like to review various methods of magic communication, look at the drawbacks, and suggest methods that the magic-using world could employ to achieve higher security.
In Mundane society, we have developed various means of encryption and obfuscation to ensure that information can be passed between users without external interference (either obtaining the information, or changing it before it reaches its destination). In the magic-using world, however, it appears that this has not been widely achieved.
Magic-users communicate in various ways: direct person-to-person contact; letters sent by owl; Floo network head-only travel; Patronus charm; two-way mirror; Protean charm; a Secret Keeper. Each of these has various advantages and disadvantages, which I will discuss before providing some suggestions for additional security.
There are several instances in the Harry Potter series of direct contact being overheard, such as the Weasley twins’ Extendable Ears, and Rita Skeeter transforming into a bug so she can listen unnoticed. The Imperturbable Charm was used with great success by Mrs. Weasley to prevent the use of the Extendable Ears, as it creates an invisible barrier around its target.
I’m not sure that the full extent of this barrier is detailed in the books, but we’re shown that it prevents eavesdropping as well as physical access to the protected space. In my opinion, this is a very useful charm and I’m not sure why it wasn’t used more extensively to protect the secrecy of direct communication.
The question of information security in the magic world first came to mind specifically because magic-users apparently have few methods available for use with the letters they send by owl. The owl can be intercepted, the letter read, and then sent on its way; both the owl and the letter itself are vulnerable.
The parchment can be sealed, but it cannot be prevented from being opened and re-sealed by a powerful Witch or Wizard. They message can be vague or obscure, but this reduces the usefulness of the information being transmitted.
Source: Archive of our Own