# What is a ciphering key?

In Hebrew language there is the term tzophen (צופן) which means cipher.

There is also a term "maphtech hatzpana" (מפתח הצפנה) which means "ciphering key".

What is a ciphering key?

Cipher, as far as I know, is a matter of resorting characters to get a meaningful message, so what "key" is needed to do so?

It might be that the Hebrew term is wrong and the meaning is "encryption key".

• With a bit of luck Yehuda can expand a bit more on the Hebrew origins of both terms. May 16 at 8:42
• The word TZOPHEN appears in the bible in various conjugations to mean to hide/hiding. Not sure when it started to mean cipher/encryption. but in hebrew sources from 2000 years ago discussing the ATBASH cipher I saw no use of this or any other term to mean cipher/encryption so thia use is probably modern but not sure. May 17 at 4:36

A cipher is defined for cryptography as "A cryptographic system using an algorithm that converts letters or sequences of bits into ciphertext."

Now it seems that the origin of the term cipher has to do with the numerical conversion of a message. However, in the realm of cryptography, a cipher is an algorithm used to obtain confidentiality. Cryptography itself means "secret writing", although modern cryptography has expanded to cover a lot more than just ciphers.

The way to keep messages secret is to transform them using the cipher algorithm using a (ciphering) key. This key is pre-established: a secret key known at both sides for symmetric ciphers such as AES or part of a public-private key pair for asymmetric algorithms such as RSA.

In asymmetric algorithms the public key is used to encrypt (enciphering) and the private key for decryption (deciphering). Only the parties that know the secret or private key should be able to gain knowledge about the message (not considering the message length); if this is the case then the cipher is considered secure.

So the ciphering key is an input to the cipher algorithm. For symmetric systems it is commonly binary. For classical ciphers such as the Caesar cipher or for asymmetric cryptography the key commonly consists of one or more numerical values. The form of the key depends entirely on the algorithm used. Digital computers do require a representation using bits though.

Cipher, as far as I know, is a matter of resorting characters to get a meaningful message, so what "key" is needed to do so?

No, in the realm of cryptography the cipher is not just resorting of characters. Modern ciphers do commonly use substitution and transposition (which could be described as "resorting I suppose), but those operation depend on the key used. The idea is that these operations are made irreversible without the secret or private key.

It might be that the Hebrew term is wrong and the meaning is "encryption key".

In my understanding the terms "ciphering key" and "encryption key" are mostly synonymous. The difference is that I would consider both the public encryption key and private decryption key of an asymmetric algorithm a "ciphering key".

Google translate does translate the term "מפתח הצפנה" to "encryption key", for what that's worth.

• "Encryption key" is indeed the correct translation of מפתח הצפנה. May 17 at 4:22