4.2 KiB
16.3: Using BIP32 in Libwally
NOTE: This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
In §16.2, you were able to use entropy to generate a seed and its related mnemonic. As you may recall from §3.5: Understanding the Descriptor, a seed is the basis of a Hierchical Deterministic (HD) Wallet, where that single seed can be used to generate many addresses. So how do you get from the seed to actual addresses? That's where BIP32 comes in.
Creating HD Addresses
To create a HD address requires starting with a seed, and then walking down the hierarchy until the point that you create addresses.
That starts off easily enough, you just generate a seed, which you already did in the previous section:
unsigned char entropy[16];
randombytes_buf(entropy, 16);
char *mnem = NULL;
lw_response = bip39_mnemonic_from_bytes(NULL,entropy,16,&mnem);
unsigned char seed[BIP39_SEED_LEN_512];
size_t seed_len;
lw_response = bip39_mnemonic_to_seed(mnem,NULL,seed,BIP39_SEED_LEN_512,&seed_len);
Generating a Root Key
With a seed in hand, you can then generate a master extended key with the bip32_key_from_seed_alloc function (or alternatively the bip32_key_from_seed, which doesn't do the alloc):
struct ext_key *key_root;
lw_response = bip32_key_from_seed_alloc(seed,sizeof(seed),BIP32_VER_TEST_PRIVATE,0,&key_root);
As you can see, you'll need to tell it what version of the key to return, in this case BIP32_VER_TEST_PRIVATE, a private testnet key.
🔗 TESTNET vs MAINNET: On mainnet, you'd instead ask for
BIP32_VER_TEST_PRIVATE.
Generating xpub & xprv
Whenever you have a key in hand, you can turn it into xpub or xprv keys for distribution with the bip32_key_to_base58 command. You just tell it whether you want a PRIVATE (xprv) or PUBLIC (xpub) key:
char *xprv;
lw_response = bip32_key_to_base58(key_root, BIP32_FLAG_KEY_PRIVATE, &xprv);
char *xpub;
lw_response = bip32_key_to_base58(key_root, BIP32_FLAG_KEY_PUBLIC, &xpub);
Understanding the Hierarchy
/* 5. Generate key for account */
struct ext_key *key_account;
uint32_t path_account[] = {BIP32_INITIAL_HARDENED_CHILD+84, BIP32_INITIAL_HARDENED_CHILD+1, BIP32_INITIAL_HARDENED_CHILD};
lw_response = bip32_key_from_parent_path_alloc(key_root,path_account,sizeof(path_account),BIP32_FLAG_KEY_PRIVATE,&key_account);
if (lw_response) {
printf("Error: bip32_key_from_parent_path_alloc failed: %d\n",lw_response);
exit(-1);
}
char *a_xprv; lw_response = bip32_key_to_base58(key_account, BIP32_FLAG_KEY_PRIVATE, &a_xprv);
if (lw_response) {
printf("Error: account bip32_key_to_base58 failed: %d\n",lw_response);
exit(-1);
}
printf("Account xprv key: %s\r\n", a_xprv);
char *a_xpub;
lw_response = bip32_key_to_base58(key_account, BIP32_FLAG_KEY_PUBLIC, &a_xpub);
if (lw_response) {
printf("Error: account bip32_key_to_base58 failed: %d\n",lw_response);
exit(-1);
}
printf("Account xpub key: %s\r\n", a_xpub);
/* 6. Generate External Adress Key */
struct ext_key *key_external;
lw_response = bip32_key_from_parent_alloc(key_account,0,BIP32_FLAG_KEY_PRIVATE,&key_external);
if (lw_response) {
printf("Error: root bip32_key_from_parent_alloc Level #1 failed: %d\n",lw_response);
exit(-1);
}
struct ext_key *key_address;
lw_response = bip32_key_from_parent_alloc(key_external,0,BIP32_FLAG_KEY_PRIVATE,&key_address);
if (lw_response) {
printf("Error: root bip32_key_from_parent_alloc Level #2 failed: %d\n",lw_response);
exit(-1);
}
/* 7. Generate Address */
char *segwit; lw_response = wally_bip32_key_to_addr_segwit(key_address,"tb",0,&segwit);
printf("[84'/0'/0'/0/0]%s\n",segwit);
/* Cleanup! */
bip32_key_free(key_address);
bip32_key_free(key_external);
bip32_key_free(key_account);
bip32_key_free(key_root);
wally_free_string(xprv);
wally_free_string(xpub);
wally_free_string(a_xprv);
wally_free_string(a_xpub);
wally_free_string(mnem);
wally_cleanup(0);
}