a786599416
Replace inaccurate GenerateKey docstring (it claimed to port Cryptographer.generateKeyString directly but the input shape differs: server uses one hex digit per call, client uses Random.Next(0,65535) per call). New doc is honest about the difference and explains why it's safe. Add EncryptForNode_FixedVector_ProducesStableOutput: a pinned AES-CBC vector that catches encoding/IV/padding regressions that would slip past the roundtrip test. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
73 lines
3.2 KiB
C#
73 lines
3.2 KiB
C#
using System.Security.Cryptography;
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using System.Text;
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namespace SVSim.BattleNode.Wire;
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/// <summary>
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/// AES-256-CBC encrypt/decrypt for the node socket channel. Port of
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/// Cryptographer.EncryptRJ256ForNode / DecryptRJ256ForNode in the decompilation.
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/// Key is prepended to ciphertext (cleartext); IV is the first 16 chars of the key.
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/// </summary>
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public static class NodeCrypto
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{
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/// <summary>
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/// Generate a fresh 32-char key for server-initiated encryption.
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/// Calls <paramref name="randHexDigit"/> 32 times expecting a value in [0,15],
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/// formats each as a single hex char, then base64-encodes the resulting 32-char ASCII
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/// string and truncates to 32 chars.
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/// </summary>
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/// <remarks>
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/// Differs from the client's <c>Cryptographer.generateKeyString</c> in input shape:
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/// the client uses <c>Random.Next(0, 65535).ToString("x")</c> per iteration (1–4 hex
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/// chars each). The output distribution is therefore different, but both produce a
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/// valid 32-char UTF-8 AES-256 key — and the client never validates the server's key
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/// since the server is decrypt-only in practice. Server-initiated encryption (e.g.
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/// for <c>synchronize</c> pushes) uses this method.
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/// </remarks>
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public static string GenerateKey(Func<int> randHexDigit)
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{
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var sb = new StringBuilder(32);
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for (var i = 0; i < 32; i++)
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{
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sb.Append(randHexDigit().ToString("x"));
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}
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var ascii = Encoding.ASCII.GetBytes(sb.ToString());
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return Convert.ToBase64String(ascii).Substring(0, 32);
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}
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/// <summary>Encrypt: returns key + base64(AES-256-CBC(plain)).</summary>
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public static string EncryptForNode(string plaintext, string key)
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{
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if (key.Length != 32)
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throw new ArgumentException($"Key must be exactly 32 chars, got {key.Length}", nameof(key));
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using var aes = Aes.Create();
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aes.KeySize = 256;
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aes.Mode = CipherMode.CBC;
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aes.Padding = PaddingMode.PKCS7;
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aes.Key = Encoding.UTF8.GetBytes(key);
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aes.IV = Encoding.UTF8.GetBytes(key.Substring(0, 16));
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using var encryptor = aes.CreateEncryptor();
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var plainBytes = Encoding.UTF8.GetBytes(plaintext);
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var cipherBytes = encryptor.TransformFinalBlock(plainBytes, 0, plainBytes.Length);
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return key + Convert.ToBase64String(cipherBytes);
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}
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/// <summary>Decrypt: input[0..32] is key, input[32..] is base64(ciphertext).</summary>
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public static string DecryptForNode(string encrypted)
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{
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if (encrypted.Length < 32)
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throw new ArgumentException("Encrypted blob is shorter than the 32-char key prefix", nameof(encrypted));
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var key = encrypted.Substring(0, 32);
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var cipherBytes = Convert.FromBase64String(encrypted.Substring(32));
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using var aes = Aes.Create();
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aes.KeySize = 256;
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aes.Mode = CipherMode.CBC;
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aes.Padding = PaddingMode.PKCS7;
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aes.Key = Encoding.UTF8.GetBytes(key);
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aes.IV = Encoding.UTF8.GetBytes(key.Substring(0, 16));
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using var decryptor = aes.CreateDecryptor();
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var plainBytes = decryptor.TransformFinalBlock(cipherBytes, 0, cipherBytes.Length);
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return Encoding.UTF8.GetString(plainBytes);
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}
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}
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