79 lines
No EOL
3 KiB
C#
79 lines
No EOL
3 KiB
C#
using System.Security.Cryptography;
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namespace IdentityShroud.Core.Security;
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public static class Encryption
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{
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private readonly record struct AlgVersion(int Version, int NonceSize, int TagSize);
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private static AlgVersion[] _versions =
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[
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new(0, 0, 0), // version 0 does not realy exist
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new(1, 12, 16), // version 1
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];
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public static byte[] Encrypt(ReadOnlySpan<byte> plaintext, ReadOnlySpan<byte> key)
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{
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const int versionNumber = 1;
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AlgVersion versionParams = _versions[versionNumber];
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int resultSize = 1 + versionParams.NonceSize + versionParams.TagSize + plaintext.Length;
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// allocate buffer for complete response
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var result = new byte[resultSize];
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result[0] = (byte)versionParams.Version;
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// make the spans that point to the parts of the result where their data is located
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var nonce = result.AsSpan(1, versionParams.NonceSize);
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var tag = result.AsSpan(1 + versionParams.NonceSize, versionParams.TagSize);
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var cipher = result.AsSpan(1 + versionParams.NonceSize + versionParams.TagSize);
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// use the spans to place the data directly in its place
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RandomNumberGenerator.Fill(nonce);
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using var aes = new AesGcm(key, versionParams.TagSize);
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aes.Encrypt(nonce, plaintext, cipher, tag);
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return result;
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}
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public static void Decrypt(ReadOnlyMemory<byte> input, ReadOnlySpan<byte> key, Span<byte> output)
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{
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AlgVersion versionParams = GetVersionParams(input);
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if (input.Length < 1 + versionParams.NonceSize + versionParams.TagSize)
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throw new ArgumentException("Cypher data is too short to be valid.", nameof(input));
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var payload = input.Span;
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ReadOnlySpan<byte> nonce = payload.Slice(1, versionParams.NonceSize);
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ReadOnlySpan<byte> tag = payload.Slice(1 + versionParams.NonceSize, versionParams.TagSize);
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ReadOnlySpan<byte> cipher = payload.Slice(1 + versionParams.NonceSize + versionParams.TagSize);
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using var aes = new AesGcm(key, versionParams.TagSize);
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try
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{
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aes.Decrypt(nonce, cipher, tag, output);
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}
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catch (CryptographicException ex)
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{
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// Tag verification failed → tampering or wrong key/nonce.
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throw new InvalidOperationException("Decryption failed – authentication tag mismatch.", ex);
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}
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}
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public static int GetDecryptedLength(ReadOnlyMemory<byte> input)
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{
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AlgVersion versionParams = GetVersionParams(input);
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int length = input.Length - (1 + versionParams.NonceSize + versionParams.TagSize);
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if (length < 0)
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throw new ArgumentException("Cypher data is too short to be valid.", nameof(input));
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return length;
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}
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private static AlgVersion GetVersionParams(ReadOnlyMemory<byte> input)
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{
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var versionNumber = (int)input.Span[0];
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if (versionNumber != 1)
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throw new ArgumentException("Invalid payload");
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return _versions[versionNumber];
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}
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} |