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Documented the block body for the GRIN wiki website #75

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Documented the block body for the GRIN wiki website #75

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1086975
Documented the block body for the GRIN wiki website
marekyggdrasil Aug 21, 2022
8da2005
Range proofs are of a variable size
marekyggdrasil Aug 21, 2022
4f2f29c
Splitting height locked kernels and NRD kernel descriptions
marekyggdrasil Aug 21, 2022
a8f5354
Block body is Transaction body
marekyggdrasil Aug 21, 2022
26cf56b
Briefly explained the NRD kernels
marekyggdrasil Aug 24, 2022
29a10dd
Explained that block body is just a transaction body
marekyggdrasil Aug 24, 2022
8aa233b
Explained the coinbase kernel
marekyggdrasil Aug 25, 2022
aa76270
Another iteration of the NRD kernel description
marekyggdrasil Aug 25, 2022
210e886
Time locks in NRD kernels are relative
marekyggdrasil Aug 25, 2022
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3 changes: 3 additions & 0 deletions docs/wiki/blocks/block-body.md
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# Block Body
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The block body contains transactions. They are aggregated into one single transaction and follow the description of a [transaction body](../transactions/transaction-body.md).
85 changes: 85 additions & 0 deletions docs/wiki/transactions/transaction-body.md
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# Transaction Body

General format of a **Transaction Body** in a Mimblewimble/Grin is basically a Mimblewimble transaction which consists of a list of **Inputs**, **Outputs** and **Kernels**.

| Field | Description | Size |
|:--------------|:----------------------|:---------------------|
| # inputs | Number of inputs | 8 bytes |
| # outputs | Number of outputs | 8 bytes |
| # kernels | Number of kernels | 8 bytes |
| inputs | Serialized inputs | 34 bytes per input |
| outputs | Serialized outputs | 42 bytes per output |
| kernels | Serialized kernels | x bytes per kernel |

The kernel size **x** depends on the kernel type. More details in its dedicated section below.

## Inputs

Each of the inputs consists of **Feature** and a **Commitment**.

| Field | Description | Size |
|:--------------|:----------------------------------------|:--------------------|
| Feature | **Plain** (0x00) or **Coinbase** (0x01) | 1 byte |
| Commitment | Pedersen commitment | 33 bytes |

## Outputs

Just as in case of the inputs, the outputs consist of **Feature** and a **Commitment** but in addition they also hold **Range proofs**

| Field | Description | Size |
|:-----------------------|:----------------------------------------|:--------------------|
| Feature | **Plain** (0x00) or **Coinbase** (0x01) | 1 byte |
| Commitment | Pedersen commitment | 33 bytes |
| Range proof size **x** | Proves the transaction is net positive | 8 bytes |
| Range proof | Proves the transaction is net positive | **x** bytes |

Note that the **range proof** is of a variable size which is indicated by its first 8 bytes.

## Kernels

Every kernel starts with **Kernel feature** which indicates how it should be deserialized. In each variant, the kernel concludes with an **Excess commitment** and a **Excess signature**. What differs them is what is in the middle. We will describe each variant separately

### Coinbase kernel

The most basic kernel that does not contain **Fee** nor **Lock height**.
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| Field | Description | Size |
|:------------------|:--------------------------------------------------------------------------------------------------|:--------------------|
| Feature | **Plain** (0x00), **Coinbase** (0x01), **Height Locked** (0x02) or **No recent duplicate** (0x03) | 1 byte |
| Excess commitment | Pedersen commitment | 33 bytes |
| Excess signature | Schnorr signature | 64 bytes |

### Plain kernel

A kernel resulting from a transaction, unlike **Coinbase** kernel it also includes **Fee** billed for the transaction.

| Field | Description | Size |
|:------------------|:--------------------------------------------------------------------------------------------------|:--------------------|
| Feature | **Plain** (0x00), **Coinbase** (0x01), **Height Locked** (0x02) or **No recent duplicate** (0x03) | 1 byte |
| Fee | Transaction fee | 8 bytes |
| Excess commitment | Pedersen commitment | 33 bytes |
| Excess signature | Schnorr signature | 64 bytes |

### Height locked kernels

The first protocol **kernel** would always consist of **Feature**, **Fee**, **Lock height** and standard **Excess commitment** and **Signature**. Starting from the V2 protocol a specific type of kernel - **height locked** kernel supports the **lock height**.

| Field | Description | Size |
|:------------------|:--------------------------------------------------------------------------------------------------|:--------------------|
| Feature | **Plain** (0x00), **Coinbase** (0x01), **Height Locked** (0x02) or **No recent duplicate** (0x03) | 1 byte |
| Fee | Transaction fee | 8 bytes |
| Lock height | Block height starting from which the kernel becomes valid | 8 bytes |
| Excess commitment | Pedersen commitment | 33 bytes |
| Excess signature | Schnorr signature | 64 bytes |

### NRD (No Recent Duplicate) kernels

When transaction is representing a creation of a payment channel it is relevant to ensure that one of the parties cannot update own kernel associated to own output in the transaction. The NRD kernels are created simultaneously and correlated preventing such an attack. More details in the [mailing list archive](https://lists.launchpad.net/mimblewimble/msg00636.html).
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| Field | Description | Size |
|:------------------|:--------------------------------------------------------------------------------------------------|:--------------------|
| Feature | **Plain** (0x00), **Coinbase** (0x01), **Height Locked** (0x02) or **No recent duplicate** (0x03) | 1 byte |
| Fee | Transaction fee | 8 bytes |
| Lock height | Block height starting from which the kernel becomes valid | 8 bytes |
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| Excess commitment | Pedersen commitment | 33 bytes |
| Excess signature | Schnorr signature | 64 bytes |