UA-.NETStandard/Stack/Opc.Ua.Security.Certificates/Common/AsnUtils.cs

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 * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
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 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
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 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
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 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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 * OTHER DEALINGS IN THE SOFTWARE.
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using System;
using System.Formats.Asn1;
using System.Globalization;
using System.Security.Cryptography;
using System.Text;

namespace Opc.Ua.Security.Certificates
{
    /// <summary>
    /// Utils for ASN.1 encoding and decoding.
    /// </summary>
    public static class AsnUtils
    {
        /// <summary>
        /// Converts a buffer to a hexadecimal string.
        /// </summary>
        internal static string ToHexString(this byte[]? buffer, bool invertEndian = false)
        {
            if (buffer == null || buffer.Length == 0)
            {
                return string.Empty;
            }

#if NET6_0_OR_GREATER
            if (!invertEndian)
            {
                return Convert.ToHexString(buffer);
            }
            else
#endif
            {
                var builder = new StringBuilder(buffer.Length * 2);

#if !NET6_0_OR_GREATER
                if (!invertEndian)
                {
                    for (int ii = 0; ii < buffer.Length; ii++)
                    {
                        builder.AppendFormat(CultureInfo.InvariantCulture, "{0:X2}", buffer[ii]);
                    }
                }
                else
#endif
                {
                    for (int ii = buffer.Length - 1; ii >= 0; ii--)
                    {
                        builder.AppendFormat(CultureInfo.InvariantCulture, "{0:X2}", buffer[ii]);
                    }
                }

                return builder.ToString();
            }
        }

        /// <summary>
        /// Converts a hexadecimal string to an array of bytes.
        /// </summary>
        internal static byte[]? FromHexString(this string? buffer)
        {
            if (buffer == null)
            {
                return null;
            }

            if (buffer.Length == 0)
            {
                return [];
            }

#if NET6_0_OR_GREATER
            return Convert.FromHexString(buffer);
#else
            const string digits = "0123456789ABCDEF";

            byte[] bytes = new byte[(buffer.Length / 2) + (buffer.Length % 2)];

            int ii = 0;

            while (ii < bytes.Length * 2)
            {
                int index = digits.IndexOf(buffer[ii], StringComparison.Ordinal);

                if (index == -1)
                {
                    break;
                }

                byte b = (byte)index;
                b <<= 4;

                if (ii < buffer.Length - 1)
                {
                    index = digits.IndexOf(buffer[ii + 1], StringComparison.Ordinal);

                    if (index == -1)
                    {
                        break;
                    }

                    b += (byte)index;
                }

                bytes[ii / 2] = b;
                ii += 2;
            }

            return bytes;
#endif
        }

        /// <summary>
        /// Writer for Public Key parameters.
        /// </summary>
        /// <remarks>
        /// https://www.itu.int/rec/T-REC-X.690-201508-I/en
        /// section 8.3 (Encoding of an integer value).
        /// </remarks>
        /// <param name="writer">The writer</param>
        /// <param name="integer">The key parameter</param>
        internal static void WriteKeyParameterInteger(
            this AsnWriter writer,
            ReadOnlySpan<byte> integer)
        {
            if (integer[0] == 0)
            {
                int newStart = 1;

                while (newStart < integer.Length)
                {
                    if (integer[newStart] >= 0x80)
                    {
                        newStart--;
                        break;
                    }

                    if (integer[newStart] != 0)
                    {
                        break;
                    }

                    newStart++;
                }

                if (newStart == integer.Length)
                {
                    newStart--;
                }

                integer = integer[newStart..];
            }

            writer.WriteIntegerUnsigned(integer);
        }

        /// <summary>
        /// Parse a X509 Tbs and signature from a byte blob with validation,
        /// return the byte array which contains the X509 blob.
        /// </summary>
        /// <param name="blob">The encoded CRL or certificate sequence.</param>
        /// <exception cref="CryptographicException"></exception>
        /// <exception cref="AsnContentException"></exception>
        public static ReadOnlyMemory<byte> ParseX509Blob(ReadOnlyMemory<byte> blob)
        {
            try
            {
                var x509Reader = new AsnReader(blob, AsnEncodingRules.DER);
                ReadOnlyMemory<byte> peekBlob = blob[..(x509Reader.PeekContentBytes().Length + 4)];
                AsnReader seqReader = x509Reader.ReadSequence(Asn1Tag.Sequence);
                if (seqReader != null)
                {
                    // Tbs encoded data
                    ReadOnlyMemory<byte> tbs = seqReader.ReadEncodedValue();

                    // Signature Algorithm Identifier
                    AsnReader sigOid = seqReader.ReadSequence();
                    string signatureAlgorithm = sigOid.ReadObjectIdentifier();
                    HashAlgorithmName name = Oids.GetHashAlgorithmName(signatureAlgorithm);

                    // Signature
                    byte[] signature = seqReader.ReadBitString(out int unusedBitCount);
                    if (unusedBitCount != 0)
                    {
                        throw new AsnContentException("Unexpected data in signature.");
                    }
                    seqReader.ThrowIfNotEmpty();
                    return peekBlob;
                }
            }
            catch (AsnContentException ace)
            {
                throw new CryptographicException("Failed to decode the X509 sequence.", ace);
            }
            throw new CryptographicException("Invalid ASN encoding for the X509 sequence.");
        }
    }
}