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https://github.com/Sea-Haven-Industries/shoc-backend.git
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77a10e38ca
- Forgot Password is limited to 3 codes an hour and 10 a day per email, and an account gets 10 failed code checks a day across every code it is sent, so new client addresses and new codes no longer buy more guesses. Refused requests answer exactly like accepted ones. - The reset email is queued to a background sender, and unregistered addresses store a row no code can match, so both paths do the same work and return without waiting on the mail provider. Each request also clears expired codes. - Code hashes are HMAC-SHA256 under a key derived with HKDF from the JWT signing secret; rows in the previous unkeyed format stop matching. - Email and code are read only from the JSON body.
61 lines
2.5 KiB
C#
61 lines
2.5 KiB
C#
using System.Globalization;
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using System.Security.Cryptography;
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using System.Text;
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namespace SeaHaven.Services.Helpers
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{
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/// <summary>
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/// Generation and hashing for emailed password reset codes. The raw code exists
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/// only in memory and in the email sent to the account holder. Hashes are keyed
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/// with a server-side key, so a copy of the database alone cannot be used to
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/// brute-force the six-digit codes offline.
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/// </summary>
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public static class PasswordResetCodeSecrets
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{
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private static readonly byte[] KeyInfo = Encoding.UTF8.GetBytes("password-reset-code-v1");
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/// <summary>
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/// Derives the code-hashing key from an existing server secret with HKDF, so no
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/// new secret is needed and the derived key is useless for anything else.
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/// </summary>
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public static byte[] DeriveKey(string serverSecret)
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{
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ArgumentException.ThrowIfNullOrEmpty(serverSecret);
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return HKDF.DeriveKey(HashAlgorithmName.SHA256, Encoding.UTF8.GetBytes(serverSecret), 32, Array.Empty<byte>(), KeyInfo);
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}
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public static string NewCode()
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{
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return RandomNumberGenerator.GetInt32(0, 1_000_000).ToString("D6", CultureInfo.InvariantCulture);
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}
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public static string NewSalt()
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{
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return Convert.ToHexString(RandomNumberGenerator.GetBytes(16)).ToLowerInvariant();
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}
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/// <summary>A value shaped like a hash that no code can match.</summary>
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public static string NewUnmatchableHash()
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{
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return Convert.ToHexString(RandomNumberGenerator.GetBytes(32)).ToLowerInvariant();
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}
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public static string Hash(byte[] key, string salt, string code)
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{
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ArgumentNullException.ThrowIfNull(key);
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ArgumentNullException.ThrowIfNull(salt);
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ArgumentNullException.ThrowIfNull(code);
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return Convert.ToHexString(HMACSHA256.HashData(key, Encoding.UTF8.GetBytes(salt + ":" + code))).ToLowerInvariant();
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}
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public static bool Matches(byte[] key, string salt, string candidate, string expectedHash)
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{
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if (string.IsNullOrEmpty(salt) || string.IsNullOrEmpty(expectedHash))
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return false;
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var actual = Encoding.ASCII.GetBytes(Hash(key, salt, candidate.Trim()));
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var expected = Encoding.ASCII.GetBytes(expectedHash);
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return CryptographicOperations.FixedTimeEquals(actual, expected);
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}
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}
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}
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