(Objective-C) 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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#import <CkoCrypt2.h>
#import <NSString.h>
#import <CkoBinData.h>

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

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];

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

// This is the 2nd test vector..
NSString *mnemonic = @"legal winner thank year wave sausage worth useful legal winner thank yellow";
NSString *passphrase = @"TREZOR";
NSString *expectedSeed = @"2e8905819b8723fe2c1d161860e5ee1830318dbf49a83bd451cfb8440c28bd6fa457fe1296106559a3c80937a1c1069be3a3a5bd381ee6260e8d9739fce1f607";
NSString *expectedMasterKey = @"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.
CkoBinData *bdSalt = [[CkoBinData alloc] init];
[bdSalt AppendString: @"mnemonic" charset: @"utf-8"];
[bdSalt AppendString: passphrase charset: @"utf-8"];

NSString *computedSeed = [crypt Pbkdf2: mnemonic charset: @"utf-8" hashAlg: @"sha512" salt: [bdSalt GetEncoded: @"hex_lower"] iterationCount: [NSNumber numberWithInt: 2048] outputKeyBitLen: [NSNumber numberWithInt: 512] encoding: @"hex_lower"];

NSLog(@"%@%@",@"Expected: ",expectedSeed);
NSLog(@"%@%@",@"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
CkoBinData *bdSeed = [[CkoBinData alloc] init];
[bdSeed AppendEncoded: computedSeed encoding: @"hex_lower"];
crypt.EncodingMode = @"hex_lower";
crypt.HashAlgorithm = @"sha512";
[crypt SetMacKeyString: @"Bitcoin seed"];
NSString *hmacSha512_hex = [crypt MacBdENC: bdSeed];

CkoBinData *bdHmac = [[CkoBinData alloc] init];
[bdHmac AppendEncoded: hmacSha512_hex encoding: @"hex_lower"];

CkoBinData *bdXprv = [[CkoBinData alloc] init];
[bdXprv AppendEncoded: @"0488ade4" encoding: @"hex_lower"];
[bdXprv AppendEncoded: @"000000000000000000" encoding: @"hex_lower"];
[bdXprv AppendEncoded: [bdHmac GetEncodedChunk: [NSNumber numberWithInt: 32] numBytes: [NSNumber numberWithInt: 32] encoding: @"hex_lower"] encoding: @"hex_lower"];
[bdXprv AppendByte: [NSNumber numberWithInt: 0]];
[bdXprv AppendEncoded: [bdHmac GetEncodedChunk: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 32] encoding: @"hex_lower"] encoding: @"hex_lower"];

// Double hash using SHA256
crypt.EncodingMode = @"hex_lower";
crypt.HashAlgorithm = @"sha256";

CkoBinData *bdHash = [[CkoBinData alloc] init];
[bdHash AppendEncoded: [crypt HashBdENC: bdXprv] encoding: @"hex_lower"];
NSString *secondHash = [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: [NSNumber numberWithInt: 0] numBytes: [NSNumber numberWithInt: 4] encoding: @"hex_lower"] encoding: @"hex_lower"];

// Base58 encode bdXprv
NSString *computedMasterKey = [bdXprv GetEncoded: @"base58"];

NSLog(@"%@%@",@"Expected Master Key: ",expectedMasterKey);
NSLog(@"%@%@",@"Computed Master Key: ",computedMasterKey);