I've been redirected here for more, or rather more accurate help from the crypto section of stackexchange.
Long story short, we have this assignment that is bugging me. We are supposed to be employees in a corporate environment that has managed to steal an encrypted message from another company of the field. Now, of course, are asked to decipher the ciphertext. The algorithm is unknown, but we know that we should get an english plaintext, but i cannot seem to find the solution.
The ciphertext is consisted of a long sequence of Fs, 5s and 6s. I have noticed stuff such as:
the only "double" sequence is 55. There's no FF or 66.
F is always followed by a 5, you cannot find F6 in the ciphertext.
As a hint, we were told that "other than the algorithm, we should also find the alphabet".
I thought of some solutions, but e.g. i don't think that simple substitution can lead in any reasonable result.
For more context, the ciphertext is here:
Any help is highly appreciated.
EDIT: @Gareth McCaughan : Nah not really, it's a university assignment.
EDIT 2: Just because there is a misconception on another thread about homework and what not: I never asked anyone to solve the exercise for me. I am asking for hints, hence the generic "any help is appreciated". I forgot to do it on this post, but on my crypto.se post i explicitly asked people to NOT solve the exercise for me, just give me possible hints that i was possibly not seeing, based on their experience. Heck, that's why i even put the ciphertext in that spoiler thing you got here, just in case anyone could help me already just by the description i gave, without seeing the ciphertext. If you think it's such a biggie, please do remove the post, i don't want to cause any confusion or drama among your users/community, would be a shame.