Bitcoin Forum

Mnemonic mnemo = new Mnemonic(Wordlist.English, WordCount.Twelve);

using Autarkysoft.Bitcoin.Encoders;
using Autarkysoft.Bitcoin.ImprovementProposals;

public BIP0039 GetBip39FromHex(string hex) => new BIP0039(Base16.Decode(hex));

Byte[] entropy = { 0xfe, 0x5e, 0xa5, 0x18, 0xfb, 0x51, 0x53, 0xd7, 
                    0x34, 0x75, 0x54, 0x52, 0x5c, 0xba, 0xc7, 0x15 }; // 128-bit entropy
            
Mnemonic mnemo = new Mnemonic(Wordlist.English, entropy);
Console.WriteLine(mnemo.ToString());

11111111 11122222 22222233 33333333 3...

bool success = PublicKey.TryRead(Base16.Decode("replace_with_pubkey_hex"), out PublicKey pubkey);
// Make sure success is true
string encrypted = pubkey.Encrypt("replace_with_message");

using PrivateKey key = new PrivateKey("replace_with_private_key_wif");
string decrypted = key.Decrypt(encrypted );

using Autarkysoft.Bitcoin;
using Autarkysoft.Bitcoin.Encoders;
using Autarkysoft.Bitcoin.ImprovementProposals;
using System;
using System.Linq;
using System.Text;

public string MnToHex(string mnemonic, BIP0039.WordLists wl = BIP0039.WordLists.English)
{
    if (string.IsNullOrWhiteSpace(mnemonic))
        throw new ArgumentNullException(nameof(mnemonic), "Seed can not be null or empty!");
    string[] allWords = BIP0039.GetAllWords(wl);

    string[] words = mnemonic.Normalize(NormalizationForm.FormKD)
                                .Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
    if (!words.All(x => allWords.Contains(x)))
    {
        throw new ArgumentException(nameof(mnemonic), "Seed has invalid words.");
    }
    if (!new int[] { 12, 15, 18, 21, 24 }.Contains(words.Length))
    {
        throw new FormatException("Invalid seed length. It should be ∈{12, 15, 18, 21, 24}");
    }

    uint[] wordIndexes = new uint[words.Length];
    for (int i = 0; i < words.Length; i++)
    {
        wordIndexes[i] = (uint)Array.IndexOf(allWords, words[i]);
    }

    int ENTCS = words.Length * 11;
    int CS = ENTCS % 32;
    int ENT = ENTCS - CS;

    byte[] entropy = new byte[(ENT / 8) + 1];

    int itemIndex = 0;
    int bitIndex = 0;
    for (int i = 0; i < entropy.Length - 1; i++)
    {
        if (bitIndex + 8 <= 11)
        {
            entropy[i] = (byte)(wordIndexes[itemIndex] >> (3 - bitIndex));
        }
        else
        {
            entropy[i] = (byte)(((wordIndexes[itemIndex] << (bitIndex - 3)) & 0xff) |
                                    (wordIndexes[itemIndex + 1] >> (14 - bitIndex)));
        }

        bitIndex += 8;
        if (bitIndex >= 11)
        {
            bitIndex -= 11;
            itemIndex++;
        }
    }

    uint mask = (1U << CS) - 1;
    entropy[^1] = (byte)(wordIndexes[itemIndex] & mask);

    return entropy.ToBase16();
}

public string HexToMn(string hex, BIP0039.WordLists wl = BIP0039.WordLists.English)
{
    byte[] entropy = Base16.Decode(hex);
    if (entropy.Length != 33)
        throw new ArgumentOutOfRangeException();

    byte[] ba = entropy.ConcatFast(new byte[3]);

    uint[] bits = new uint[9];
    for (int i = 0, j = 0; i < ba.Length - 1; i += 4, j++)
    {
        bits[j] = (uint)(ba[i + 3] | (ba[i + 2] << 8) | (ba[i + 1] << 16) | (ba[i] << 24));
    }

    int itemIndex = 0;
    int bitIndex = 0;
    uint[] wordIndexes = new uint[24];
    for (int i = 0; i < 24; i++)
    {
        if (bitIndex + 11 <= 32)
        {
            wordIndexes[i] = (bits[itemIndex] << bitIndex) >> 21;
        }
        else
        {
            wordIndexes[i] = ((bits[itemIndex] << bitIndex) >> 21) |
                                (bits[itemIndex + 1] >> (53 - bitIndex));
        }

        bitIndex += 11;
        if (bitIndex >= 32)
        {
            bitIndex -= 32;
            itemIndex++;
        }
    }

    StringBuilder sb = new StringBuilder(wordIndexes.Length * 8);
    string[] allWords = BIP0039.GetAllWords(wl);
    for (int i = 0; i < wordIndexes.Length; i++)
    {
        sb.Append($"{allWords[wordIndexes[i]]} ");
    }

    sb.Length--;
    return sb.ToString();
}

string path = $"Autarkysoft.Bitcoin.ImprovementProposals.BIP0039WordLists.{wl}.txt";