We have two tags:
After the recent boom of steganography puzzles, which have been well received, do we really need cryptography?
Here are the two tag wiki excerpts:
Hidden data concealed in otherwise unsuspicious pictures, text, and/or audio.
And
A puzzle concerning techniques for secure communication in the presence of (hostile) third parties.
To me they are both the same thing - hidden data.
The only differences I see is that cryptography mentions (hostile) third parties...
Both involve concealing a secret message so that its meaning is not apparent, but in cryptography the message is hidden within apparent gibberish, while in steganography it's hidden within a different message which seems to have a totally innocuous meaning. From Wikipedia:
The advantage of steganography over cryptography alone is that the intended secret message does not attract attention to itself as an object of scrutiny. Plainly visible encrypted messages—no matter how unbreakable—arouse interest, and may in themselves be incriminating in countries where encryption is illegal. Thus, whereas cryptography is the practice of protecting the contents of a message alone, steganography is concerned with concealing the fact that a secret message is being sent, as well as concealing the contents of the message.
There is much confusion over terminology in this area of knowledge. From Wikipedia (emphasis mostly mine):
Until modern times, cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (called plaintext) into unintelligible text (called ciphertext).[10] Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. A cipher (or cypher) is a pair of algorithms that create the encryption and the reversing decryption.
[...]
In colloquial use, the term "code" is often used to mean any method of encryption or concealment of meaning. However, in cryptography, code has a more specific meaning. It means the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a code word (for example, "wallaby" replaces "attack at dawn").
Cryptanalysis is the term used for the study of methods for obtaining the meaning of encrypted information without access to the key normally required to do so; i.e., it is the study of how to crack encryption algorithms or their implementations.
Some use the terms cryptography and cryptology interchangeably in English, while others (including US military practice generally) use cryptography to refer specifically to the use and practice of cryptographic techniques and cryptology to refer to the combined study of cryptography and cryptanalysis.
So what does this tell us about how we should use the tags on PSE? Well, I have two different suggestions for that:
Synonymise cryptography and ciphers.
As we can see, code and cryptograms, as well as encoded-message and cipher, already count as synonyms of the master tag cipher. (It's taken quite a while to get there though!) Now codes and ciphers are technically two different things (ciphers usually replace each letter of the plaintext with a different letter or symbol, while codes replace words of the plaintext with different words or phrases. If these two separate concepts are considered similar enough to be synonymised on PSE, we may as well put the whole of cryptography under the one tag.
Use cryptography only for questions about cryptography rather than "decrypt the cipher" puzzles.
Until today I thought this was how cryptography was being used already. It seems that my perception was more or less correct about a year ago, when it was questions such as How can our secret agent produce a cryptographically secure random number? and Snow White and the Secret Message (Secret Sharing Problem) and Two Sheriffs and Eavesdroppers and A Game of Phones that bore the tag. But standards have apparently slipped since then, and this tag is now being used for actual cipher puzzles, on which it might as well be replaced by cipher.
Proposition 1 would be simpler to implement, but I'm not sure if all the questions tagged cryptography would really fit with the cipher tag. Modern cryptography has advanced further than simple ciphers, and covers things like the RSA algorithm too.
Proposition 2 would involve retagging a bunch of questions 'inappropriately' tagged cryptography and editing the tag wiki to clarify its usage. This could take a while, but once it's done, we would at least have clear usage guidance for the tags covering two separate types of question.
