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Correct .NET 11 RC1 libraries release notes #10570

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Correct .NET 11 RC1 libraries release notes #10570

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20 changes: 13 additions & 7 deletions release-notes/11.0/preview/rc1/libraries.md
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Expand Up @@ -98,8 +98,6 @@ The `Memory<byte>` and `ReadOnlyMemory<byte>` schemas remain non-nullable (`"typ
For a union with object-shaped cases, specify the classifier on the union to select the case from its distinguishing property names:

```csharp
#:property LangVersion=preview

using System.Text.Json;
using System.Text.Json.Serialization;

Expand Down Expand Up @@ -213,17 +211,25 @@ On an Apple M1 Ultra running macOS Tahoe 26.6, encrypting a 16-byte payload with

## AES Key Wrap support

The `Aes` class now supports the unpadded AES Key Wrap algorithm defined by RFC 3394 ([dotnet/runtime #132477](https://github.com/dotnet/runtime/pull/132477)). The new `EncryptKeyWrap`, `DecryptKeyWrap`, `TryDecryptKeyWrap`, and `GetKeyWrapLength` methods complement the padded AES-KWP APIs added earlier in .NET 11.
The `Aes` class now supports the unpadded AES Key Wrap algorithm defined by RFC 3394 ([dotnet/runtime #132477](https://github.com/dotnet/runtime/pull/132477)). The new `EncryptKeyWrap`, `DecryptKeyWrap`, `TryDecryptKeyWrap`, and `GetKeyWrapLength` methods complement the padded AES-KWP APIs added in .NET 10.

@jeffhandley jeffhandley Sep 9, 2026

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This change is correct; thanks. dotnet/runtime#130490


The APIs provide array-returning and span-based overloads for wrapping cryptographic keys, including scenarios used by JOSE libraries.

## Breaking changes
```csharp
using System.Security.Cryptography;

### Numeric conversions are now correctly rounded
using Aes aes = Aes.Create();
aes.Key = RandomNumberGenerator.GetBytes(32);

Starting in .NET 11 Preview 7, conversions between `decimal` and binary floating-point types, and conversions from `BigInteger` to binary floating-point types, round the exact source value once to the nearest representable destination value ([dotnet/runtime #130565](https://github.com/dotnet/runtime/pull/130565), [dotnet/runtime #130566](https://github.com/dotnet/runtime/pull/130566)). The previous conversions could lose significant digits or round through an intermediate value, so existing binaries and code rebuilt with a .NET 11 Preview 7 or later SDK can produce different results.

@jeffhandley jeffhandley Sep 9, 2026

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We missed catching this breaking change note in the Preview 7 release notes as we didn't document it until RC1.

#10542 (comment)

Please check with @tannergooding before removing this per their comment linked there, and I too thought it was a pretty noteworthy thing to cover, albeit late.

byte[] keyToWrap = RandomNumberGenerator.GetBytes(16);
byte[] wrappedKey = aes.EncryptKeyWrap(keyToWrap);
byte[] unwrappedKey = aes.DecryptKeyWrap(wrappedKey);

For example, converting the `double` literal `1.23` to `decimal` now preserves the exact binary floating-point value rather than producing `1.23`. If a value is intended to be decimal, use a decimal literal such as `1.23m` instead of converting a `double` literal. Update tests and serialized expected values that relied on the previous result; there is no compatibility switch to restore the former conversion algorithms. For complete guidance, see [dotnet/docs#55743](https://github.com/dotnet/docs/issues/55743).
Console.WriteLine(
CryptographicOperations.FixedTimeEquals(keyToWrap, unwrappedKey));
```

## Breaking changes

### HTTP metrics are observable instruments

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