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Remove byte[] allocation in VerifyRsa / VerifyECDsa #2589

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merged 2 commits into from
May 13, 2024
+47 −0
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Remove byte[] allocation in VerifyRsa / VerifyECDsa #2589

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f7ac71a
Remove byte[] allocation in VerifyRsa / VerifyECDsa
eerhardt May 9, 2024
ceb1ce8
Respond to PR feedback
eerhardt May 13, 2024
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47 changes: 47 additions & 0 deletions src/Microsoft.IdentityModel.Tokens/AsymmetricAdapter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,10 @@
// Licensed under the MIT License.

using System;
#if NET6_0_OR_GREATER
using System.Buffers;
using System.Diagnostics;
#endif
using System.Security.Cryptography;
using Microsoft.IdentityModel.Logging;

Expand Down Expand Up @@ -330,12 +334,20 @@ private static bool VerifyUsingOffsetNotFound(byte[] bytes, int offset, int coun

private bool VerifyECDsa(byte[] bytes, byte[] signature)
{
#if NET6_0_OR_GREATER
return VerifyUsingSpan(isRSA: false, bytes, signature);
#else
return ECDsa.VerifyHash(HashAlgorithm.ComputeHash(bytes), signature);
#endif
}

private bool VerifyUsingOffsetECDsa(byte[] bytes, int offset, int count, byte[] signature)
{
#if NET6_0_OR_GREATER
return VerifyUsingSpan(isRSA: false, bytes.AsSpan(offset, count), signature);
#else
return ECDsa.VerifyHash(HashAlgorithm.ComputeHash(bytes, offset, count), signature);
#endif
}

private byte[] DecryptWithRsa(byte[] bytes)
Expand Down Expand Up @@ -373,14 +385,49 @@ private byte[] SignUsingOffsetRsa(byte[] bytes, int offset, int count)

private bool VerifyRsa(byte[] bytes, byte[] signature)
{
#if NET6_0_OR_GREATER
return VerifyUsingSpan(isRSA: true, bytes, signature);
#else
return RSA.VerifyHash(HashAlgorithm.ComputeHash(bytes), signature, HashAlgorithmName, RSASignaturePadding);
#endif
}

private bool VerifyUsingOffsetRsa(byte[] bytes, int offset, int count, byte[] signature)
{
#if NET6_0_OR_GREATER
return VerifyUsingSpan(isRSA: true, bytes.AsSpan(offset, count), signature);
#else
return RSA.VerifyHash(HashAlgorithm.ComputeHash(bytes, offset, count), signature, HashAlgorithmName, RSASignaturePadding);
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Since you already have the HashAlgorithmName, why not just call VerifyData and let the framework do the hashing for you (which won't create a temporary array)?

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and let the framework do the hashing for you (which won't create a temporary array)?

This doesn't appear to be the case. When I step into it, I get:

https://github.com/dotnet/runtime/blob/9926d609dab5929941b7924a04521ea2c2df27f3/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSA.cs#L661-L662

Which allocates the byte[].

Here is my test code (on windows):

using System.Security.Cryptography;

RSA rSA = RSA.Create();

byte[] data = [0x1, 0x2, 0x3, 0x4];

byte[] signature = rSA.SignData(data, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

for (int i = 0; i < 1_000; i++)
{
    rSA.VerifyData(data, signature, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
}

image

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Should I submit a similar PR to RSA and ECDsa in dotnet/runtime?

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@bartonjs bartonjs May 9, 2024 •
edited
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It looks like VerifyData(ReadOnlySpan) uses span-hashing, but VerifyData(byte[]) uses array-hashing; because we never override public virtual bool VerifyData(byte[], int, int, byte[], HashAlgorithmName, RSASignaturePadding). So the change in dotnet/runtime to make everyone happier is probably to override that method on all N of our RSA types. (RSACryptoServiceProvider, RSACng, RSAOpenSsl, RSASecurityTransforms, RSAAndroid, and maybe up to double that from the "RSA.Create()" types). Which is going to involve a lot of copy/paste of the argument validation. Bleh.

Here, though, it means

return rsa.VerifyData(
#if NET5_OR_GREATER
    bytes.AsSpan(offset, count),
#else
    bytes, offset, count,
#endif
    signature,
    HashAlgorithmName,
    RSASignaturePadding);

should take your numbers down to 0 (for .NET5+)

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@eerhardt eerhardt May 9, 2024 •
edited
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RSA is still allocating here:

https://github.com/dotnet/runtime/blob/9926d609dab5929941b7924a04521ea2c2df27f3/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSA.cs#L322

image

HashData returns a new byte[].

Test Code:

using System.Security.Cryptography;

RSA algo = RSA.Create();

byte[] data = [0x1, 0x2, 0x3, 0x4];

byte[] signature = algo.SignData(data, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

for (int i = 0; i < 1_000; i++)
{
    algo.VerifyData(data.AsSpan(), signature, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
}

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Weird, since it should have hit the if (this is IRuntimeAlgorithm) above and bypassed the allocation routine. Must've missed a marker interface somewhere, too.

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@eerhardt eerhardt May 10, 2024 •
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In my case, this is an RSABCrypt, which doesn't implement that interface.

https://github.com/dotnet/runtime/blob/acd31754892ab0431ac2c40038f541ffa7168be7/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSABCrypt.cs#L11

On Linux it looks like we get an RSAWrapper, which also doesn't implement it:

https://github.com/dotnet/runtime/blob/9926d609dab5929941b7924a04521ea2c2df27f3/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSAWrapper.cs#L10

#endif
}

#if NET6_0_OR_GREATER
private bool VerifyUsingSpan(bool isRSA, ReadOnlySpan<byte> bytes, byte[] signature)
{
int hashByteLength = HashAlgorithm.HashSize / 8;
byte[] array = null;
Span<byte> hash = hashByteLength <= 256 ? stackalloc byte[256] : array = ArrayPool<byte>.Shared.Rent(hashByteLength);
hash = hash.Slice(0, hashByteLength);

try
{
bool hashResult = HashAlgorithm.TryComputeHash(bytes, hash, out int bytesWritten);
Debug.Assert(hashResult && bytesWritten == hashByteLength, "HashAlgorithm.TryComputeHash failed");

return isRSA ?
RSA.VerifyHash(hash, signature, HashAlgorithmName, RSASignaturePadding) :
ECDsa.VerifyHash(hash, signature);
}
finally
{
if (array is not null)
{
ArrayPool<byte>.Shared.Return(array, clearArray: true);
}
}
}
#endif

#region DESKTOP related code
#if DESKTOP
internal byte[] DecryptWithRsaCryptoServiceProviderProxy(byte[] bytes)
Expand Down
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