(Swift 3,4,5...) 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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func chilkatTest() {
    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    let crypt = CkoCrypt2()!

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

    // This is the 2nd test vector..
    var mnemonic: String? = "legal winner thank year wave sausage worth useful legal winner thank yellow"
    var passphrase: String? = "TREZOR"
    var expectedSeed: String? = "2e8905819b8723fe2c1d161860e5ee1830318dbf49a83bd451cfb8440c28bd6fa457fe1296106559a3c80937a1c1069be3a3a5bd381ee6260e8d9739fce1f607"
    var expectedMasterKey: 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.
    let bdSalt = CkoBinData()!
    bdSalt.append("mnemonic", charset: "utf-8")
    bdSalt.append(passphrase, charset: "utf-8")

    var computedSeed: String? = crypt.pbkdf2(mnemonic, charset: "utf-8", hashAlg: "sha512", salt: bdSalt.getEncoded("hex_lower"), iterationCount: 2048, outputKeyBitLen: 512, encoding: "hex_lower")

    print("Expected: \(expectedSeed!)")
    print("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
    let bdSeed = CkoBinData()!
    bdSeed.appendEncoded(computedSeed, encoding: "hex_lower")
    crypt.encodingMode = "hex_lower"
    crypt.hashAlgorithm = "sha512"
    crypt.setMacKeyString("Bitcoin seed")
    var hmacSha512_hex: String? = crypt.macBdENC(bdSeed)

    let bdHmac = CkoBinData()!
    bdHmac.appendEncoded(hmacSha512_hex, encoding: "hex_lower")

    let bdXprv = CkoBinData()!
    bdXprv.appendEncoded("0488ade4", encoding: "hex_lower")
    bdXprv.appendEncoded("000000000000000000", encoding: "hex_lower")
    bdXprv.appendEncoded(bdHmac.getEncodedChunk(32, numBytes: 32, encoding: "hex_lower"), encoding: "hex_lower")
    bdXprv.appendByte(0)
    bdXprv.appendEncoded(bdHmac.getEncodedChunk(0, numBytes: 32, encoding: "hex_lower"), encoding: "hex_lower")

    // Double hash using SHA256
    crypt.encodingMode = "hex_lower"
    crypt.hashAlgorithm = "sha256"

    let bdHash = CkoBinData()!
    bdHash.appendEncoded(crypt.hashBdENC(bdXprv), encoding: "hex_lower")
    var secondHash: String? = crypt.hashBdENC(bdHash)
    bdHash.clear()
    bdHash.appendEncoded(secondHash, encoding: "hex_lower")

    // Append the 1st 4 bytes of the bdHash to bdXprv.
    bdXprv.appendEncoded(bdHash.getEncodedChunk(0, numBytes: 4, encoding: "hex_lower"), encoding: "hex_lower")

    // Base58 encode bdXprv
    var computedMasterKey: String? = bdXprv.getEncoded("base58")

    print("Expected Master Key: \(expectedMasterKey!)")
    print("Computed Master Key: \(computedMasterKey!)")

}