Are there semantic differences between encrypt, cipher and encode?

Question

In French we have specific words to mean

• "take plaintext and transform it into encrypted data": chiffrer
• "take encrypted data and, knowing the key, decrypt it": déchiffrer
• "take encrypted data and, without knowning the key, decrypt it (via brute force or whatever)": décrypter

We would not be French if there was not a web site dedicated to this question: https://chiffrer.info/. Note that the word crypter does not exist (the counterpart of the existing décrypter)

I was wondering if there are similar differences in English, spcifically between the words "to encrypt" / "to decrypt", "to cipher" and "to encode" / "to decode".

Wikipedia seems to use encrypt and decrypt as the equivalent of my two first versions.

Cipher (used as a verb by extension of the noun) seems to be a kind of encryption (substitution). Encode is rather the action to transform something into something via an algorithm.

My question is especially around the concept of "decrypting without a key" which I cannot find a word for.

Answer 1

I think the major English verbs for decrypting are:

• decrypt — the most common term that specifically means converting from ciphertext to plaintext (though it can also be used metaphorically). This is what the intended recipient does, but it's also what the NSA does.
• decode — a much broader term that sometimes specifically implies decryption, but can also be used for any other kind of conversion from a less-readable to a more-readable form, even a very simple conversion such as from foo+%22bar%22+baz to foo "bar" baz (decoding a URL component).
• decipher — similar to decrypt and decode, but nowadays tends to imply a laborious/manually-intensive process. This sometimes means that you're not the intended recipient (since the intended recipient would have the key, so should be able to decrypt easily), but not necessarily: something like "We had the key, but our decryption machine was broken, so Lt. Peters had to decipher the message one letter at a time" is fine. Decipher can also be metaphorical, such as deciphering an unknown ancient language, or an odd facial expression, or someone's illegible handwriting; the common factor is the greater-than-intended effort involved in recovering the meaning.
• break or crack — these are general-purpose verbs that are often applied when defeating someone else's encryption: "I've cracked the code!" But unlike with the other verbs above, you can't say something like *"I broke the message"; you break the cipher, not the message. Like all the other verbs I've mentioned, it's often used metaphorically, such as in "cracking the genetic code".
• cryptanalyze — though I shouldn't really call this a "major" verb. It's quite rare; the corresponding noun crypanalysis is a bit more common. It also means breaking or cracking a code — or trying to do so.

Incidentally, you mention the verb cipher, but I think the verb encipher is more common.

Answer 2

According to https://dictionary.cambridge.org/dictionary/english/decrypt, decrypt covers the intended (eg with the key) and unintended (eg by decryption analysis software) cases.

I don't think it's case of being pedantic, as @cobaltduck says in the comments - I think that there's just one word.

On a side note, the difference between en/decoding and en/decrypting is that with encoding the process is public and is done for a specific purpose other than hiding information: to send data down a wire or internet connection, for example, which relies on public encoding protocols which are part of various technical specifications, all of which are publically available.

Encryption refers to when the encoding is done specifically to make a message unreadable to unauthorised viewers. Often, the word "decode" is used to refer to "unauthorised decryption", that is decrypting a message without the decryption key. However, the word "decrypt" can be usually be substituted for this with no change of meaning.

Answer 3

When you decrypt a message without having the key, you crack or break its code:

Cracking the Code (Central Intelligence Agency)

Can You Crack a Code? (Federal Bureau of Investigation)

Apart from that:

• Encrypt, cipher, and encode are pretty much synonymous (M-W Unabridged defines encrypt as "to encipher or encode")
• Ditto for decrypt, deciper, and decode (M-W again defines decrypt as "to decipher or decode")

Answer 4

This answer is withing the scope of technology and the internet
Let's start with cipher as it's the easiest word. Cipher is primarily a noun, and the verb is much less commonly used. Cipher in itself is usually used to describe a very simple encryption algorithm. Something that could be undone by a human being that knows how to reverse it. Ciphered things are deciphered.

Encrypt is complicated. This is the generic word that cipher falls under. This often refers to very complex algorithms used by computers that can achieve some cool features by using complex math. Encryption can be done so some can write some can read, all can write some can read, or some can write some can read. Anything encrypted has to be encrypted.

Finally encode is used for a process that just changes something. This usual refers to a known public posses and is not done for security reasons. For instance data in URL's is encoded to not have illegal characters. Videos are encoded to not take up as much space. Encoding is sometimes lossy. The opposite of encode is decode. Unfortunately the word decode has a lot more meaning than decode, as it can be used as a synonym to decipher, where encode is not really a synonym to cipher.

For your final point, encrypting without a key may be best defined as decode