besu/docs/Privacy/Explanation/Privacy-Groups.md

description: Privacy

Privacy Groups

A privacy group is a group of nodes identified by a unique privacy group ID by Orion. Each private transaction is stored in Orion with the privacy group ID.

The Pantheon nodes maintain the public world state for the blockchain and a private state for each privacy group. The private states contain data that is not shared in the globally replicated world state. Private transactions read and write to the private world state for the privacy group, and read from the public world state.

Privacy Types

Pantheon implements two types of privacy:

• EEA-compliant privacy - private transactions include privateFor as the recipient.
• Pantheon-extended privacy - private transactions include privacyGroupId as the recipient.

Both privacy types create privacy groups and store private transactions with their privacy group in Orion.

!!! note The Orion nodes are not shown above for clarity only. To send private transactions, each Pantheon node must have an associated Orion node.

EEA-compliant Privacy

In our privacy implementation complying with the EEA Client Specification the group of nodes specified by privateFromand privateFor form a privacy group and are given a unique privacy group ID by Orion.

!!! example The diagram above illustrates two privacy groups enabling:

* A, B, and C to send transactions that are private from D 
* A, C, and D to send transactions that are private from B 

Using EEA-compliant privacy, to send private transactions between A, B, and C, A initialises a contract in a private transaction with
B and C specified as the `privateFor` and A specified as the `privateFrom`. Initialising the contract 
creates a privacy group consisting of A, B, and C. For the ABC private state to remain consistent, 
A, B, and C must be included on transactions (as either `privateFrom` or `privateFor`) even if they are 
between two of the three parties.

To send private transactions between A, C, and D, C initialises a different contract in a private transaction with
A and D specified as the `privateFor` and C specified as the `privateFrom`. Initialising the contract 
creates a privacy group consisting of  A, C, and D. For the ACD private state to remain consistent, 
A, C, and D must be included on transactions (as either `privateFrom` or `privateFor`) even if they are 
between two of the three parties.

Pantheon-extended Privacy

In our extended privacy implementation, a privacy group is created using priv_createPrivacyGroup and private transactions sent to the privacy group ID.

!!! example Using the same privacy groups as above.

Using Pantheon-extended privacy, to send private transactions between A, B, and C, A creates a privacy 
group consisting of A, B, and C. The privacy group ID is specified when sending private transactions and 
A, B, and C are recipients of all private transactions sent to the privacy group. 

To send private transactions between A, C, and D, A creates a privacy group consisting of A, C, and D.
The privacy group ID of this group is specified when sending private transactions with A, C, and D 
as recipients.