(VB.NET) BIP39 Compute Binary Seed from Mnemonic

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Creates a binary seed from a mnemonic. Uses the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes).

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' This example assumes the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim crypt As New Chilkat.Crypt2

' Test with the test vectors at https://github.com/trezor/python-mnemonic/blob/master/vectors.json

' This is the 2nd test vector..
Dim mnemonic As String = "legal winner thank year wave sausage worth useful legal winner thank yellow"
Dim passphrase As String = "TREZOR"
Dim expectedSeed As String = "2e8905819b8723fe2c1d161860e5ee1830318dbf49a83bd451cfb8440c28bd6fa457fe1296106559a3c80937a1c1069be3a3a5bd381ee6260e8d9739fce1f607"
Dim expectedMasterKey As String = "xprv9s21ZrQH143K2gA81bYFHqU68xz1cX2APaSq5tt6MFSLeXnCKV1RVUJt9FWNTbrrryem4ZckN8k4Ls1H6nwdvDTvnV7zEXs2HgPezuVccsq"

' The mnemonic sentence (in UTF-8 NFKD) used as the password.
' The string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt.
' The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function.
' The length of the derived key is 512 bits (= 64 bytes). 

' We want the computed seed to be lowercase hex, therefore our salt must also be hex.
' The seed is the keyword "mnemonic" + passphrase (in this case is "TREZOR") converted to hex.
Dim bdSalt As New Chilkat.BinData
bdSalt.AppendString("mnemonic","utf-8")
bdSalt.AppendString(passphrase,"utf-8")

Dim computedSeed As String = crypt.Pbkdf2(mnemonic,"utf-8","sha512",bdSalt.GetEncoded("hex_lower"),2048,512,"hex_lower")

Debug.WriteLine("Expected: " & expectedSeed)
Debug.WriteLine("Computed: " & computedSeed)

' To compute the hd_master_key, duplicate this Python code:

'     def to_hd_master_key(seed: bytes, testnet: bool = False) -> str:
'         if len(seed) != 64:
'             raise ValueError("Provided seed should have length of 64")
' 
'         # Compute HMAC-SHA512 of seed
'         seed = hmac.new(b"Bitcoin seed", seed, digestmod=hashlib.sha512).digest()
' 
'         # Serialization format can be found at: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#Serialization_format
'         xprv = b"\x04\x88\xad\xe4"  # Version for private mainnet
'         if testnet:
'             xprv = b"\x04\x35\x83\x94"  # Version for private testnet
'         xprv += b"\x00" * 9  # Depth, parent fingerprint, and child number
'         xprv += seed[32:]  # Chain code
'         xprv += b"\x00" + seed[:32]  # Master key
' 
'         # Double hash using SHA256
'         hashed_xprv = hashlib.sha256(xprv).digest()
'         hashed_xprv = hashlib.sha256(hashed_xprv).digest()
' 
'         # Append 4 bytes of checksum
'         xprv += hashed_xprv[:4]
' 
'         # Return base58
'         return b58encode(xprv)


' First compute the HMAC-SHA512 of the computedSeed
Dim bdSeed As New Chilkat.BinData
bdSeed.AppendEncoded(computedSeed,"hex_lower")
crypt.EncodingMode = "hex_lower"
crypt.HashAlgorithm = "sha512"
crypt.SetMacKeyString("Bitcoin seed")
Dim hmacSha512_hex As String = crypt.MacBdENC(bdSeed)

Dim bdHmac As New Chilkat.BinData
bdHmac.AppendEncoded(hmacSha512_hex,"hex_lower")

Dim bdXprv As New Chilkat.BinData
bdXprv.AppendEncoded("0488ade4","hex_lower")
bdXprv.AppendEncoded("000000000000000000","hex_lower")
bdXprv.AppendEncoded(bdHmac.GetEncodedChunk(32,32,"hex_lower"),"hex_lower")
bdXprv.AppendByte(0)
bdXprv.AppendEncoded(bdHmac.GetEncodedChunk(0,32,"hex_lower"),"hex_lower")

' Double hash using SHA256
crypt.EncodingMode = "hex_lower"
crypt.HashAlgorithm = "sha256"

Dim bdHash As New Chilkat.BinData
bdHash.AppendEncoded(crypt.HashBdENC(bdXprv),"hex_lower")
Dim secondHash As String = crypt.HashBdENC(bdHash)
bdHash.Clear()
bdHash.AppendEncoded(secondHash,"hex_lower")

' Append the 1st 4 bytes of the bdHash to bdXprv.
bdXprv.AppendEncoded(bdHash.GetEncodedChunk(0,4,"hex_lower"),"hex_lower")

' Base58 encode bdXprv
Dim computedMasterKey As String = bdXprv.GetEncoded("base58")

Debug.WriteLine("Expected Master Key: " & expectedMasterKey)
Debug.WriteLine("Computed Master Key: " & computedMasterKey)