API proposal: Add ReadOnlySpan<byte> to IDataProtector (un)Protect

Background and Motivation

Add ReadOnlySpan<byte> overrides so consumer apps are able to avoid a extra array allocation+blockbuffer.copy every time they try to protect\unprotect data.

Proposed API

namespace Microsoft.AspNetCore.DataProtection;

public interface IDataProtector : IDataProtectionProvider
{
+    byte[] Protect(ReadOnlySpan<byte> plaintext);

+    byte[] Unprotect(ReadOnlySpan<byte> protectedData);
}

Usage Examples

var buffer = new ArrayBufferWriter<byte>();

// write some data to buffer
var blob = new Data { Some = "Payload" };
MessagePackSerializer.Serialize(buffer, blob);

IDataProtector protector = provider.CreateProtector("demo");
return protector.Protect(buffer.WrittenSpan);

Alternative Designs

namespace Microsoft.AspNetCore.DataProtection;

public interface IDataProtector : IDataProtectionProvider
{
+    byte[] Protect(ReadOnlySpan<byte> plaintext) => this.Protect(plaintext.ToArray())

+    byte[] Unprotect(ReadOnlySpan<byte> protectedData) => this.Unprotect(protectedData.ToArray())
}

Risks

All of the existing protector implementations have to be changed to implement this change. We could also have a default interface implementation to prevent it breaking to aggressively.

Performance impact should be minimal, and actually open the possibility for apps to avoid a unnecessary array copy, if people use the api correctly

[amcasey]

To get the perf win, we’d have to avoid allocating the array in the API implementation as well, so we’d probably need/want to update these too:

Microsoft.AspNetCore.DataProtection.AuthenticatedEncryption.IAuthenticatedEncryptor.Decrypt(System.ArraySegment<byte> ciphertext, System.ArraySegment<byte> additionalAuthenticatedData) -> byte[]!
Microsoft.AspNetCore.DataProtection.AuthenticatedEncryption.IAuthenticatedEncryptor.Encrypt(System.ArraySegment<byte> plaintext, System.ArraySegment<byte> additionalAuthenticatedData) -> byte[]!
Microsoft.AspNetCore.DataProtection.ISecret.WriteSecretIntoBuffer(System.ArraySegment<byte> buffer) -> void
Microsoft.AspNetCore.DataProtection.Secret.Secret(System.ArraySegment<byte> value) -> void
Microsoft.AspNetCore.DataProtection.Secret.WriteSecretIntoBuffer(System.ArraySegment<byte> buffer) -> void

And probably these, if only for consistency:

static Microsoft.AspNetCore.Cryptography.KeyDerivation.KeyDerivation.Pbkdf2(string! password, byte[]! salt, Microsoft.AspNetCore.Cryptography.KeyDerivation.KeyDerivationPrf prf, int iterationCount, int numBytesRequested) -> byte[]!
Microsoft.AspNetCore.DataProtection.IPersistedDataProtector.DangerousUnprotect(byte[]! protectedData, bool ignoreRevocationErrors, out bool requiresMigration, out bool wasRevoked) -> byte[]!
Microsoft.AspNetCore.DataProtection.Secret.Secret(byte[]! value) -> void
Microsoft.AspNetCore.DataProtection.ITimeLimitedDataProtector.Protect(byte[]! plaintext, System.DateTimeOffset expiration) -> byte[]!
Microsoft.AspNetCore.DataProtection.ITimeLimitedDataProtector.Unprotect(byte[]! protectedData, out System.DateTimeOffset expiration) -> byte[]!
static Microsoft.AspNetCore.DataProtection.DataProtectionAdvancedExtensions.Protect(this Microsoft.AspNetCore.DataProtection.ITimeLimitedDataProtector! protector, byte[]! plaintext, System.TimeSpan lifetime) -> byte[]!

[adityamandaleeka]

Triage: optimizing this is likely going to help in some hot paths. We believe the API needs some design work though.

Note: We’ll need to make sure netstandard2.0 works.