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Add FixedTimeEquals and other crypto helper routines as public API
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63 changes: 63 additions & 0 deletions
63
...urity.Cryptography.Primitives/src/System/Security/Cryptography/CryptographicOperations.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,63 @@ | ||
| // Licensed to the .NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
| // See the LICENSE file in the project root for more information. | ||
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| using System.Runtime.CompilerServices; | ||
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| namespace System.Security.Cryptography | ||
| { | ||
| public static class CryptographicOperations | ||
| { | ||
| /// <summary> | ||
| /// Determine the equality of two byte sequences in an amount of time which depends on | ||
| /// the length of the sequences, but not the values. | ||
| /// </summary> | ||
| /// <param name="left">The first buffer to compare.</param> | ||
| /// <param name="right">The second buffer to compare.</param> | ||
| /// <returns> | ||
| /// <c>true</c> if <paramref name="left"/> and <paramref name="right"/> have the same | ||
| /// values for <see cref="ReadOnlySpan{T}.Length"/> and the same contents, <c>false</c> | ||
| /// otherwise. | ||
| /// </returns> | ||
| /// <remarks> | ||
| /// This method compares two buffers' contents for equality in a manner which does not | ||
| /// leak timing information, making it ideal for use within cryptographic routines. | ||
| /// This method will short-circuit and return <c>false</c> only if <paramref name="left"/> | ||
| /// and <paramref name="right"/> have different lengths. | ||
| /// | ||
| /// Fixed-time behavior is guaranteed in all other cases, including if <paramref name="left"/> | ||
| /// and <paramref name="right"/> reference the same address. | ||
| /// </remarks> | ||
| [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)] | ||
| public static bool FixedTimeEquals(ReadOnlySpan<byte> left, ReadOnlySpan<byte> right) | ||
| { | ||
| // NoOptimization because we want this method to be exactly as non-short-circuiting | ||
| // as written. | ||
| // | ||
| // NoInlining because the NoOptimization would get lost if the method got inlined. | ||
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| if (left.Length != right.Length) | ||
| { | ||
| return false; | ||
| } | ||
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| int length = left.Length; | ||
| int accum = 0; | ||
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| for (int i = 0; i < length; i++) | ||
| { | ||
| accum |= left[i] - right[i]; | ||
| } | ||
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| return accum == 0; | ||
| } | ||
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| [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)] | ||
| public static void ZeroMemory(Span<byte> buffer) | ||
| { | ||
| // NoOptimize to prevent the optimizer from deciding this call is unnecessary | ||
| // NoInlining to prevent the inliner from forgetting that the method was no-optimize | ||
| buffer.Clear(); | ||
| } | ||
| } | ||
| } |
109 changes: 109 additions & 0 deletions
109
src/System.Security.Cryptography.Primitives/tests/FixedTimeEqualsTests.cs
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,109 @@ | ||
| // Licensed to the .NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
| // See the LICENSE file in the project root for more information. | ||
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| using System.Buffers; | ||
| using System.Reflection; | ||
| using System.Runtime.CompilerServices; | ||
| using Xunit; | ||
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| namespace System.Security.Cryptography.Primitives.Tests | ||
| { | ||
| public static class FixedTimeEqualsTests | ||
| { | ||
| [Theory] | ||
| [InlineData(0)] | ||
| [InlineData(1)] | ||
| [InlineData(128 / 8)] | ||
| [InlineData(256 / 8)] | ||
| [InlineData(512 / 8)] | ||
| [InlineData(96)] | ||
| [InlineData(1024)] | ||
| public static void EqualReturnsTrue(int byteLength) | ||
| { | ||
| byte[] rented = ArrayPool<byte>.Shared.Rent(byteLength); | ||
| Span<byte> testSpan = new Span<byte>(rented, 0, byteLength); | ||
| RandomNumberGenerator.Fill(testSpan); | ||
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| byte[] rented2 = ArrayPool<byte>.Shared.Rent(byteLength); | ||
| Span<byte> testSpan2 = new Span<byte>(rented2, 0, byteLength); | ||
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| testSpan.CopyTo(testSpan2); | ||
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| bool isEqual = CryptographicOperations.FixedTimeEquals(testSpan, testSpan2); | ||
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| ArrayPool<byte>.Shared.Return(rented); | ||
| ArrayPool<byte>.Shared.Return(rented2); | ||
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| Assert.True(isEqual); | ||
| } | ||
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| [Theory] | ||
| [InlineData(1)] | ||
| [InlineData(128 / 8)] | ||
| [InlineData(256 / 8)] | ||
| [InlineData(512 / 8)] | ||
| [InlineData(96)] | ||
| [InlineData(1024)] | ||
| public static void UnequalReturnsFalse(int byteLength) | ||
| { | ||
| byte[] rented = ArrayPool<byte>.Shared.Rent(byteLength); | ||
| Span<byte> testSpan = new Span<byte>(rented, 0, byteLength); | ||
| RandomNumberGenerator.Fill(testSpan); | ||
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| byte[] rented2 = ArrayPool<byte>.Shared.Rent(byteLength); | ||
| Span<byte> testSpan2 = new Span<byte>(rented2, 0, byteLength); | ||
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| testSpan.CopyTo(testSpan2); | ||
| testSpan[testSpan[0] % testSpan.Length] ^= 0xFF; | ||
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| bool isEqual = CryptographicOperations.FixedTimeEquals(testSpan, testSpan2); | ||
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| ArrayPool<byte>.Shared.Return(rented); | ||
| ArrayPool<byte>.Shared.Return(rented2); | ||
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| Assert.False(isEqual); | ||
| } | ||
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| [Theory] | ||
| [InlineData(1)] | ||
| [InlineData(128 / 8)] | ||
| [InlineData(256 / 8)] | ||
| [InlineData(512 / 8)] | ||
| [InlineData(96)] | ||
| [InlineData(1024)] | ||
| public static void DifferentLengthsReturnFalse(int byteLength) | ||
| { | ||
| byte[] rented = ArrayPool<byte>.Shared.Rent(byteLength); | ||
| Span<byte> testSpan = new Span<byte>(rented, 0, byteLength); | ||
| RandomNumberGenerator.Fill(testSpan); | ||
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| byte[] rented2 = ArrayPool<byte>.Shared.Rent(byteLength); | ||
| Span<byte> testSpan2 = new Span<byte>(rented2, 0, byteLength); | ||
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| testSpan.CopyTo(testSpan2); | ||
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| bool isEqualA = CryptographicOperations.FixedTimeEquals(testSpan, testSpan2.Slice(0, byteLength - 1)); | ||
| bool isEqualB = CryptographicOperations.FixedTimeEquals(testSpan.Slice(0, byteLength - 1), testSpan2); | ||
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| ArrayPool<byte>.Shared.Return(rented); | ||
| ArrayPool<byte>.Shared.Return(rented2); | ||
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| Assert.False(isEqualA, "value, value missing last byte"); | ||
| Assert.False(isEqualB, "value missing last byte, value"); | ||
| } | ||
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| [Fact] | ||
| public static void HasCorrectMethodImpl() | ||
| { | ||
| Type t = typeof(CryptographicOperations); | ||
| MethodInfo mi = t.GetMethod(nameof(CryptographicOperations.FixedTimeEquals)); | ||
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| // This method cannot be optimized, or it loses its fixed time guarantees. | ||
| // It cannot be inlined, or it loses its no-optimization guarantee. | ||
| Assert.Equal( | ||
| MethodImplAttributes.NoInlining | MethodImplAttributes.NoOptimization, | ||
| mi.MethodImplementationFlags); | ||
| } | ||
| } | ||
| } |
8 changes: 8 additions & 0 deletions
8
src/System.Security.Cryptography.Primitives/tests/Performance/Configurations.props
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| @@ -0,0 +1,8 @@ | ||
| <?xml version="1.0" encoding="utf-8"?> | ||
| <Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003"> | ||
| <PropertyGroup> | ||
| <BuildConfigurations> | ||
| netcoreapp; | ||
| </BuildConfigurations> | ||
| </PropertyGroup> | ||
| </Project> |
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