Learn English – Semantic difference between “spectator”, “beholder”, “observer” and “viewer”

Overrated means that people hold it in higher esteem than they ought to. Overrated implies that people have a (too) high opinion.

Overvalued means that people place too high a monetary value on the thing in question. They may over value it because they overrate it, but the converse is not necessarily true.

In the case of the expression "overrated and overvalued" I suspect that there is a possiblity that it is being used for emphasis, but one would have to see it in context to see whether a literal interpretation is apt or whether it should be taken more figuratively.

In French, there are two words, "chiffrer" and "crypter"; theoretically, the latter would mean "to encrypt but without knowledge of the key, i.e. as part of an attack" (it is more often encountered as "décrypter" which means "to decrypt without prior knowledge of the key"). Relatively few French-speaking programmers are even aware of that distinction, and the French translations of many applications (including Outlook Express) use "crypter" in places where they should use "chiffrer".

In English, I do not think that this distinction actually exists. "Encipher" and "chiffrer" both come from the Arabic "sifr" which means "zero", while "encrypt" and "crypter" come from the Greek "kryptos" (hidden, secret). The use of "sifr" can apparently be traced back to Giovan Battista Bellaso, who published in 1553 cryptographic methods in Latin (as was normal at the time) but with Italian titles such as "La Cifra" and "Novi et singolari modi di cifrare". His point was that his cryptographic techniques involved some computations with numbers, and in 16th century Italy, mathematics was still an import from old Greek by way of Arab writers, brought to Christian Europe during the Crusades. Hence the use of the Arabic root.

In that sense, one could say that "to encipher" means "to encrypt, with some mathematics involved in the process". By definition, this covers any encryption in which a computer was used, so the terms "encipher" and "encrypt" are practically synonymous.