!!! Overview[1]
[{$pagename}] is a piece of [data], known only to the parties involved, in a [secure connection]. 

[{$pagename}] can be a:
* [password]
* [passphrase]
* [credential]
* [PIN]
* [MBUN number]
* [Token]
* [Cookie]
* any array of randomly chosen [bytes].

[{$pagename}] is either shared beforehand between the communicating parties, in which case it can also be called a [Pre-Shared Key], or it is created at the start of the communication [session] by using a [Key-Exchange] [protocol], for instance using [Public Key] [cryptography] such as [Diffie-Hellman] or using [Symmetric Key] [cryptography] such as [Kerberos].

[{$pagename}] can be used for [authentication] using methods such as [challenge-response] or it can be fed to a [Key Derivation Function] to produce one or more keys to use for [encryption] and/or [MAC]ing of messages.

[{$pagename}] is often provisioned as a [QR-code] or preprogrammed into a [hard token].

[{$pagename}] is usually combined with an [Initialization Vector] ([IV]) to make unique [session] and [{$pagename}]. An example of this is the derived unique key per transaction method.

[{$pagename}] is also often used as an [authentication] measure in [APIs].[{$pagename}] is a secret value that has been computed using a [key agreement] [algorithm] and is used as input to a [Key Derivation Function]. ([NIST.SP.800-107])

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [Shared secret|Wikipedia:Shared_secret|target='_blank'] - based on information obtained 2016-12-27-