> For the complete documentation index, see [llms.txt](https://docs.zongsoft.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zongsoft.com/documentation/en/framework/core/common/checksum.md).

# Checksums

Checksum Calculation, parsing and verification of checksum structures.

`Checksum` represents the named hash check value, which consists of the algorithm name and byte array. It supports calculations, parsing, validation, string conversion, type conversion, and JSON serialization.

## Core Members

| member                     | Description                                             |
| -------------------------- | ------------------------------------------------------- |
| `Name`                     | Hash algorithm name, such as `MD5`, `SHA256`, `SHA512`. |
| `Value`                    | Check value byte array.                                 |
| `IsEmpty`                  | Whether the check value is empty.                       |
| `Compute` / `ComputeAsync` | Calculate checksum from byte data or stream.            |
| `Verify` / `VerifyAsync`   | Verify that the data matches the current check value.   |
| `Parse` / `TryParse`       | Parse check value from `Name:Hex` text.                 |

This page uses an existing test from the framework ChecksumTest; the shared field \_data is 1024 bytes of data generated by the test class, and assertions are used to clarify the expected results. Discussions currently does not use Checksum directly.

## Calculate Checksum

Source: [framework/Zongsoft.Core/test/Common/ChecksumTest.cs](https://github.com/Zongsoft/framework/blob/main/Zongsoft.Core/test/Common/ChecksumTest.cs#L71) (excerpt; see source for context).

{% code title="ChecksumTest.cs" %}

```csharp
public void Compute()
{
	var checksum1 = Checksum.Compute("SHA256", _data);
	Assert.False(checksum1.IsEmpty);
	Assert.False(checksum1.Value.IsEmpty);
	Assert.Equal("SHA256", checksum1.Name, true);
	Assert.Equal(SHA256.HashSizeInBytes, checksum1.Value.Length);
	Assert.NotEmpty(checksum1.ToString());
	Assert.StartsWith("SHA256:", checksum1.ToString());

	var checksum2 = new Checksum(SHA256.HashData(_data));
	Assert.False(checksum2.IsEmpty);
	Assert.False(checksum2.Value.IsEmpty);
	Assert.Equal("SHA256", checksum2.Name, true);
	Assert.Equal(SHA256.HashSizeInBytes, checksum2.Value.Length);
	Assert.NotEmpty(checksum2.ToString());
	Assert.StartsWith("SHA256:", checksum2.ToString());

	Assert.Equal(checksum1.Name, checksum2.Name, true);
	Assert.True(checksum1.Value.Span.SequenceEqual(checksum2.Value.Span));
	Assert.Equal(checksum1, checksum2);
}
```

{% endcode %}

`Compute` will create a hash algorithm based on the name and calculate the corresponding check value.

## Validate Data

Source: [framework/Zongsoft.Core/test/Common/ChecksumTest.cs](https://github.com/Zongsoft/framework/blob/main/Zongsoft.Core/test/Common/ChecksumTest.cs#L111) (excerpt; see source for context).

{% code title="ChecksumTest.cs" %}

```csharp
public void Verify()
{
	var checksum = Checksum.Compute("SHA3-512", _data);
	Assert.False(checksum.IsEmpty);
	Assert.False(checksum.Value.IsEmpty);

	var data = new byte[_data.Length];
	Array.Copy(_data, data, data.Length);

	Assert.True(checksum.Verify(data));
	Assert.True(checksum.Verify(_data));
	Assert.False(checksum.Verify(Randomizer.Generate(512)));
	Assert.False(checksum.Verify(Randomizer.Generate(data.Length)));
}
```

{% endcode %}

Streaming data can use `Verify(Stream)` or `VerifyAsync(Stream)`.

## Parse and Convert

`Checksum.ToString()` outputs `Name:Hex` format, and `Parse` can restore this format.

Source: [framework/Zongsoft.Core/test/Common/ChecksumTest.cs](https://github.com/Zongsoft/framework/blob/main/Zongsoft.Core/test/Common/ChecksumTest.cs#L95) (excerpt; see source for context).

{% code title="ChecksumTest.cs" %}

```csharp
public void Parse()
{
	var checksum = Checksum.Compute("SHA512", _data);
	Assert.False(checksum.IsEmpty);
	Assert.False(checksum.Value.IsEmpty);
	Assert.Equal("SHA512", checksum.Name, true);
	Assert.Equal(SHA512.HashSizeInBytes, checksum.Value.Length);
	Assert.NotEmpty(checksum.ToString());
	Assert.StartsWith("SHA512:", checksum.ToString());

	var result = Checksum.Parse(checksum.ToString());
	Assert.False(result.IsEmpty);
	Assert.Equal(checksum, result);
}
```

{% endcode %}

`Checksum` has built-in type converters and JSON converters, so it can be used with `Convert` and `Serializer.Json`.

## Related Resources

* [Checksum.cs](https://github.com/Zongsoft/framework/blob/main/Zongsoft.Core/src/Common/Checksum.cs)
* [ChecksumTest.cs](https://github.com/Zongsoft/framework/blob/main/Zongsoft.Core/test/Common/ChecksumTest.cs)


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