Elementary S01E11 - Dirty Laundry
Computers only appeared for a short period of time, but they were crucial to solving this case.While investigating the computer of the victim, Holmes notices that a few family pictures are very big (1 GB), and correctly concludes that they hide other important information (in this case videos).
The art of hiding messages within other messages is called steganography, and is a very interesting subject. If done right, there really is almost no way to detect the additional information.
Hiding 1GB of data inside a photo that should take 1000 times less space, is however, a huge mistake. Normally the hidden data is just a fraction of the container (usually a photo or video).
Holmes mentions steganography as "security by obscurity". Although technically correct, computer scientists usually use this term for something else. It is used to describe bad practices where companies (or individuals) don't publish their encryption algorithms in the hope that this will strengthen their security. Scientists consider this bad practice because good encryption should be strong without hiding some details, and hiding the algorithm makes it harder to verify that no mistakes were made.
Also, computer scientists see steganography more as an extension to cryptography than as a replacement. The real purpose of steganography is generally to transmit/hide information without the adversary even knowing, whereas encryption just makes it hard/impossible for the attacker to read the data.
Spies clearly need steganography to avoid raising suspicions, however, they would most likely also encrypt the hidden data. This makes finding the hidden data harder, and furthermore doesn't reveal anything in case someone suspects steganography.
As such it's very unlikely that Holmes could just extract the hidden data. Not only would he need to have the correct program to extract the data (unlikely), but he would also need to be lucky that the data wasn't encrypted. However, on second thought, it might not be that unrealistic. If the spies were not really good at computers, they might just follow protocols (which explains, why so much data was stored in few photos), and use standard software.
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| Holmes' decoding program |
Elementary S01E12 - M.
A disappointing episode (wrt computer science). Only one noticeable reference to computers and that one was far from realistic.M. and Moriarty use encryption to chat between each other. However, M. is shown to read and write encrypted messages directly instead of going through plain text. This is not how current encryption works. If M. could read the message without decoding first, it would be a highly trivial algorithm that could be cracked within seconds.
In real world, encrypted communication relies on a key (or a key pair for public-key cryptography) and reading/writing messages is impossible without that key. The producers should have shown M. enter that key to see the decrypted message (or to write one), but then the writers would have needed to think about what the message actually said.
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| Encrypted communication ... |
Unrelated to computer science: Holmes mentions to the NYPD that M. entered the apartment through the backdoor, and that he was a skilled lock picker. While it is difficult to distinguish good and bad lock pickers, it is possible to see if a lock has been picked or not: the lock picking tools leave tiny characteristic scratches inside the lock. As far as I know, bump keys are however undetectable.
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