BouncyCastle EC math is slow in Blazor WebAssembly

[JVanloofsvelt]

It takes about a second to derive the next key from an ExtendedKey. Perhaps this library can make use of JSInterop for the Webcrypto APIs when the platform is 'browser'.

[NicolasDorier]

I am surprised it even works. WASM does not support Span? Because if you use the netstandard2.1 version of NBitcoin it is not using Bouncycastle, but something which should be more efficient.

[NicolasDorier]

I can do a special build of NBitcoin for WASM environment, but you will need to guide me here about what should be done for browser environment.

[JVanloofsvelt]

I built it with following compilation symbols set:

• NOCUSTOMSSLVALIDATION
• NETSTANDARD
• NO_ARRAY_FILL
• NULLABLE_SHIMS
• USEBC
• NONATIVEHASH
• NO_NATIVESHA1
• NO_NATIVERIPEMD160
• NO_NATIVE_RFC2898_HMACSHA512
• NO_NATIVERIPEMD160
• NO_NATIVE_HMACSHA512

This way, I managed to build it for target 'netstandard2.0'. Blazor WASM has no support for System.Security.Cryptography, that's why I toggled "USEBC" (and the other NO_NATIVE...'s). Or is there perhaps a more efficient implementation that is not using System.Security.Cryptography? (in that case I must have missed it)

I don't recall exactly if I was able to use Span, I can investigate this later.

[NicolasDorier]

Can you try to toggle HAS_SPAN?

[NicolasDorier]

Also check if you can use

using (var sha = new SHA256Managed())
			{
				return sha.ComputeHash(data, offset, count);
			}

So we can find what is supported or not. Same with SHA512Managed

[NicolasDorier]

I checked the code, toggling HAS_SPAN might already improve things if WASM support it.

[JVanloofsvelt]

I will try. Should this speed up the bouncy castle EC math?

I can try the SHA256Managed, but this is probably not the slowest part.

[NicolasDorier]

If you set HAS_SPAN it will use BC only for hash things. Not EC.

[JVanloofsvelt]

I tried it again, now targetting 'netstandard2.1'.

I had to add these 2 compilation symbols, because System.Security.Cryptography is not supported in wasm:

• NO_NATIVE_HMACSHA512
• NO_NATIVE_RFC2898_HMACSHA512

However, the project won't compile like this because the BouncyCastle source files get removed from the project when targetting 'netstandard2.1', while BouncyCastle is the fallback for the native HMACSHA512 that is now missing. I can restore the files by editing the csproj file to switch RemoveBC off:
<RemoveBC>false</RemoveBC>

Furthermore, I also had to remove the compilation symbol NO_BC

There are a few more issues that I can fix, but the result is that key derivation still runs slow in the browser.

[JVanloofsvelt]

Also check if you can use

using (var sha = new SHA256Managed())
			{
				return sha.ComputeHash(data, offset, count);
			}

So we can find what is supported or not. Same with SHA512Managed

They are not supported.
EDIT: I was wrong, they are supported. HMACSHA is not however.

[JVanloofsvelt]

@NicolasDorier please review my pull request:
https://github.com/JVanloofsvelt/NBitcoin/pull/1

As I wrote earlier, managed SHA256 and SHA512 are not supported in Blazor wasm. After applying the changes from my patch/pull-request, you should be able to build the project for netstandard2.1 and get it to work in Blazor wasm. You'll need to set RemoveBC to false, and add the following compilation symbols:

NO_NATIVESHA1;NONATIVEHASH;NO_NATIVE_HMACSHA512;NO_NATIVE_RFC2898_HMACSHA512

Unlike my first attempt at compiling it for Blazor, I am not forcing the use of Bouncy Castle with the USEBC compilation symbol.

Now the sad news: in Blazor wasm it takes my system 300-500ms to derive an ExtPubKey from a parent key, which is slow.

[NicolasDorier]

@JVanloofsvelt you did not open the PR on the right repo, you did on your fork. I will check what I can do about the RemoveBC. I should be smarter about it.

Your PR seems good.

[NicolasDorier]

I think rather than <ItemGroup Condition=" '$(RemoveBC)' == 'true' "> in the csproj, I should just look for the NO_BC constant.

Now the sad news: in Blazor wasm it takes my system 300-500ms to derive an ExtPubKey from a parent key, which is slow.

Have you tried to set HAS_SPAN ?

[NicolasDorier]

@JVanloofsvelt I am wondering if instead of relying on BC, we could not just import SHA256Managed.cs inside NBitcoin (keep it internal, change the namespace)

After all, this is open source.

[NicolasDorier]

Looking at the source code of dotnet I found implementation:

https://github.com/dotnet/runtime/blob/1d9e50cb4735df46d3de0cee5791e97295eaf588/src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/SHAHashProvider.Browser.cs

Which is very strange, as the name of the file seems to indicate it is supported by browsers oO

But this say otherwise : https://docs.microsoft.com/en-us/dotnet/core/compatibility/cryptography/5.0/cryptography-apis-not-supported-on-blazor-webassembly