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8b8c59589d
This PR encompasses two complementing purposes: A documentation on verifying an Intel SGX evidence as produced by WAMR, including a guide for verification without an Intel SGX-enabled platform. This also contains a small addition to the RA sample to extract specific information, such as whether the enclave is running in debug mode. A C# sample to verify evidence on trusted premises (and without Intel SGX). Evidence is generated on untrusted environments, using Intel SGX.
109 lines
4.9 KiB
C#
109 lines
4.9 KiB
C#
/*
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* Copyright (C) 2024 Intel Corporation.
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* Copyright (C) 2024 University of Neuchatel, Switzerland.
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*
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* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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*/
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using System.Diagnostics;
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using System.Runtime.InteropServices;
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using System.Security.Cryptography;
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using System.Text;
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using System.Text.Json;
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// Set the reference values below
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byte[] mrEnclaveReference =
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{
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0xDA, 0xE0, 0xDA, 0x2F, 0x8A, 0x53, 0xA0, 0xB4, 0x8F, 0x92, 0x6A, 0x3B, 0xC0, 0x48, 0xD6, 0xA9,
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0x67, 0xD4, 0x7C, 0x86, 0x19, 0x86, 0x76, 0x6F, 0x8F, 0x5A, 0xB1, 0xC0, 0xA8, 0xD8, 0x8E, 0x44
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};
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byte[] mrSignerReference =
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{
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0x83, 0xD7, 0x19, 0xE7, 0x7D, 0xEA, 0xCA, 0x14, 0x70, 0xF6, 0xBA, 0xF6, 0x2A, 0x4D, 0x77, 0x43,
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0x03, 0xC8, 0x99, 0xDB, 0x69, 0x02, 0x0F, 0x9C, 0x70, 0xEE, 0x1D, 0xFC, 0x08, 0xC7, 0xCE, 0x9E
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};
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const ushort securityVersionReference = 0;
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const ushort productIdReference = 0;
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string nonce = "This is a sample.\0"; // Notice the \0 at the end, which is mandatory as C-strings are terminated with this char
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string evidenceAsString = """{"type":"sgx_ecdsa","report_base64":"[..]","report_len":[..]}""";
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string wasmFilePath = "../build/wasm-app/test.wasm";
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// Parse and compute the claims
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EvidenceJson? evidenceAsJson = JsonSerializer.Deserialize<EvidenceJson>(evidenceAsString, new JsonSerializerOptions
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{
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PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower
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});
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Debug.Assert(evidenceAsJson != null, "The evidence cannot be parsed.");
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byte[] wasmFileContent = await File.ReadAllBytesAsync(wasmFilePath);
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byte[] nonceAsBytes = Encoding.UTF8.GetBytes(nonce);
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byte[] computedUserData = await ComputeUserData(wasmFileContent, nonceAsBytes);
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byte[] evidenceAsBytes = Convert.FromBase64String(evidenceAsJson.ReportBase64);
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Evidence evidence = new(evidenceAsBytes);
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int libRatsReturnValue = LibRats.VerifyEvidenceFromJson(evidenceAsString, await ComputeUserData(wasmFileContent, nonceAsBytes));
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// Compare and display the results
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Console.WriteLine($"User data, evidence: {BitConverter.ToString(evidence.UserData)}");
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Console.WriteLine($"User Data, computed: {BitConverter.ToString(computedUserData)}");
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Console.WriteLine($"Do the two user data match? {evidence.UserData.SequenceEqual(computedUserData)}");
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Console.WriteLine($"MrEnclave: {BitConverter.ToString(evidence.MrEnclave)}");
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Console.WriteLine($"Do the MrEnclave match? {mrEnclaveReference.SequenceEqual(evidence.MrEnclave)}");
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Console.WriteLine($"MrSigner: {BitConverter.ToString(evidence.MrSigner)}");
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Console.WriteLine($"Do the MrSigner match? {mrSignerReference.SequenceEqual(evidence.MrSigner)}");
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Console.WriteLine($"Security Version: {evidence.SecurityVersion}, expected: {securityVersionReference}");
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Console.WriteLine($"Product ID: {evidence.ProductId}, expected: {productIdReference}");
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Console.WriteLine($"VerifyJsonUsingLibrats returned: {libRatsReturnValue:X}");
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// Compute the user data as computed by WAMR
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static async ValueTask<byte[]> ComputeUserData(byte[] wasmFileContent, byte[] nonce)
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{
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using var sha256 = SHA256.Create();
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var wasmFileContentHash = sha256.ComputeHash(wasmFileContent);
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using MemoryStream stream = new();
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await stream.WriteAsync(wasmFileContentHash);
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await stream.WriteAsync(nonce);
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stream.Position = 0;
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byte[] computedUserData = await sha256.ComputeHashAsync(stream);
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return computedUserData;
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}
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/// <summary>
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/// The layout of the JSON is given by librats.
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/// </summary>
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class EvidenceJson
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{
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public required string Type { get; init; }
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public required string ReportBase64 { get; init; }
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public required int ReportLen { get; init; }
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}
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/// <summary>
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/// The start of the _report_body_t struct from Intel SGX is at offset 0x30.
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/// </summary>
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/// <remarks>
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/// _report_body_t struct: https://github.com/intel/linux-sgx/blob/a1eeccba5a72b3b9b342569d2cc469ece106d3e9/common/inc/sgx_report.h#L93-L111
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/// Attestation flow: https://www.intel.com/content/www/us/en/developer/articles/code-sample/software-guard-extensions-remote-attestation-end-to-end-example.html
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/// </remarks>
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class Evidence(byte[] evidenceAsBytes)
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{
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public byte[] MrEnclave => evidenceAsBytes[0x70..0x90];
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public byte[] MrSigner => evidenceAsBytes[0xB0..0xD0];
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public ushort ProductId => BitConverter.ToUInt16(evidenceAsBytes.AsSpan(0x130, 2));
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public ushort SecurityVersion => BitConverter.ToUInt16(evidenceAsBytes.AsSpan(0x132, 2));
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public byte[] UserData => evidenceAsBytes[0x170..0x190];
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}
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static class LibRats
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{
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/// <summary>
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/// Verifies the evidence using librats native function.
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/// </summary>
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/// <remarks>
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/// Original signature: int librats_verify_evidence_from_json(const char *json_string, const uint8_t *hash);
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/// </remarks>
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[DllImport("/usr/local/lib/librats/librats_lib.so", EntryPoint = "librats_verify_evidence_from_json")]
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public static extern int VerifyEvidenceFromJson(string json, byte[] hash);
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}
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