Learn English – the semantical difference between reliable and trustworthy

The OED gives the following definitions of reliable and dependable:

Reliable—1. That may be relied on.

1a. Of a person, information, etc.: able to be trusted; in which reliance or confidence may be placed; trustworthy, safe, sure.

1b. orig. U.S. Of a product, service, etc.: consistently good in quality or performance; dependable.

Dependable—That may be depended on; trustworthy, reliable.

Both definitions list the other word in their definitions, with no special qualifiers attached. In addition, both words use the word trustworthy, also without qualifiers. Therefore, it is safe to say that the two are synonyms and may be equally used.

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.