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151 lines (128 loc) · 4.33 KB
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using System.Formats.Cbor;
namespace NpgsqlRestClient.Fido2;
public static class CborDecoder
{
internal static ILogger? Logger;
public static AttestationObject? DecodeAttestationObject(byte[] data)
{
try
{
var reader = new CborReader(data, CborConformanceMode.Lax);
string fmt = "none";
byte[] authData = [];
Dictionary<object, object>? attStmt = null;
var mapLength = reader.ReadStartMap();
for (int i = 0; i < mapLength; i++)
{
var key = reader.ReadTextString();
switch (key)
{
case "fmt":
fmt = reader.ReadTextString();
break;
case "authData":
authData = reader.ReadByteString();
break;
case "attStmt":
attStmt = ReadMap(reader);
break;
default:
reader.SkipValue();
break;
}
}
reader.ReadEndMap();
return new AttestationObject
{
Fmt = fmt,
AuthData = authData,
AttStmt = attStmt
};
}
catch (Exception e)
{
// Never log the payload itself (attacker-controlled); length + exception is enough to diagnose.
Logger?.LogWarning(e,
"Failed to decode CBOR attestation object ({Length} bytes): {Message}",
data?.Length ?? 0, e.Message);
return null;
}
}
private static Dictionary<object, object> ReadMap(CborReader reader)
{
var result = new Dictionary<object, object>();
var mapLength = reader.ReadStartMap();
for (int i = 0; i < mapLength; i++)
{
var key = ReadValue(reader);
var value = ReadValue(reader);
if (key != null)
result[key] = value!;
}
reader.ReadEndMap();
return result;
}
private static object? ReadValue(CborReader reader)
{
var state = reader.PeekState();
return state switch
{
CborReaderState.UnsignedInteger => reader.ReadInt64(),
CborReaderState.NegativeInteger => reader.ReadInt64(),
CborReaderState.ByteString => reader.ReadByteString(),
CborReaderState.TextString => reader.ReadTextString(),
CborReaderState.StartArray => ReadArray(reader),
CborReaderState.StartMap => ReadMap(reader),
CborReaderState.Boolean => reader.ReadBoolean(),
CborReaderState.Null => ReadNull(reader),
CborReaderState.Tag => ReadTaggedValue(reader),
CborReaderState.HalfPrecisionFloat or
CborReaderState.SinglePrecisionFloat or
CborReaderState.DoublePrecisionFloat => reader.ReadDouble(),
_ => SkipAndReturnNull(reader)
};
}
private static object? ReadNull(CborReader reader)
{
reader.ReadNull();
return null;
}
private static object? SkipAndReturnNull(CborReader reader)
{
reader.SkipValue();
return null;
}
private static object?[] ReadArray(CborReader reader)
{
var length = reader.ReadStartArray();
if (length is null)
{
// Indefinite-length array (legal in lax conformance mode): read until end marker.
var items = new List<object?>();
while (reader.PeekState() != CborReaderState.EndArray)
{
items.Add(ReadValue(reader));
}
reader.ReadEndArray();
return [.. items];
}
var result = new object?[length.Value];
for (int i = 0; i < result.Length; i++)
{
result[i] = ReadValue(reader);
}
reader.ReadEndArray();
return result;
}
private static object? ReadTaggedValue(CborReader reader)
{
reader.ReadTag(); // Read and discard the tag
return ReadValue(reader);
}
}
public class AttestationObject
{
public string Fmt { get; set; } = "none";
public byte[] AuthData { get; set; } = [];
public Dictionary<object, object>? AttStmt { get; set; }
}