!!! Overview 
Symmetric Key [Cryptography]
[{$pagename}] is when an [Encrypted] [message] exchange using a [Symmetric Key] requires the use of the same key by all parties involved for both [encryption] and [decryption].[{$pagename}] necessitates [distributing the key|Key-Exchange] to all participants.

[{$pagename}] allows all parties must trust each other, because they can read each other's messages.

Physical distribution of symmetric keys is the safest because an unencrypted electronic transmission of a key would be vulnerable to theft. Physical key distribution would make symmetric keys hard to use in an environment with a large number of users. Even with Physical distribution, the keys are still vulnerable to theft.

However, often some application uses a clever combination of encryption schemes to distribute symmetric keys over the network for background authentication. 

[{$pagename}] [{$applicationname}] refers you to Wikipedia: [Symmetric-key_algorithm|Wikipedia:Symmetric-key_algorithm|target='_blank'][{$pagename}] [Cryptographic Algorithms] (sometimes known as [secret-key] [algorithms]) transform data in a way that is fundamentally difficult to undo without knowledge of a [secret key]. The key is [symmetric] because the same key is used for a [encryption] and [decryption]). 

Symmetric keys are often known by more than one [entity]; however, the [key] shall not be disclosed to [entities] that are not authorized access to the data protected by that algorithm and [secret-key]. [{$pagename}] [algorithms] are used, for example,
* To provide data [confidentiality]; the same key is used to [encrypt] and [decrypt|Decryption] data;
* To provide source and [integrity] [authentication] services in the form of [Message Authentication Codes] ([MACs]); the same key is used to generate the MAC and to validate it. MACs normally employ either a symmetric key-encryption algorithm or a cryptographic hash function as their cryptographic primitive;
* As part of the [Key-Establishment] process
* To generate deterministic [random] numbers

[Advanced Encryption Standard] ([AES]) and [ChaCha20] are the most popular [{$pagename}] methods. [AES] is a [Block Cipher], with 128-bit block sizes. [ChaCha20] is a [Stream Cipher].

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [Symmetric-key_algorithm|Wikipedia:Symmetric-key_algorithm|target='_blank'] - based on information obtained 2018-08-12-