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Wallet-File-Formats-and-Types.md

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Wallet file format

Wallet files are files in the configured wallets folder (~/.skycoin/wallets by default) that have the extension .wlt. When the daemon/client start, all *.wlt files from the configured wallets folder are loaded. If any wallet file is detected as invalid, the daemon/client will not start. Wallet files MUST NOT be modified while the daemon/client are running, or else those modifications may be overwritten by the daemon/client when it is quit.

Wallet files contain data in JSON format. Although there can be multiple types of wallet files with different data structures, they all must contain a "meta" field pointing to a JSON object.

When the wallet file is loaded, the JSON data is scanned for the meta.type field. Then, this type is used to determine the rest of the wallet file structure to load.

Wallet metadata

The wallet file's "meta" field object has the following fields:

  • coin: Required. Can be skycoin or bitcoin. Refers to the address format. All fiber coins will be skycoin since they all have the same address format. Note that bitcoin coin type is not supported in the daemon, but the cli has limited support for it.
  • cryptoType: The encryption method for encrypted wallets. The only value should be scrypt-chacha20poly1305.
  • encrypted: A boolean indicating if the wallet is encrypted or not
  • filename: The filename of the wallet
  • label: The label of the wallet, to display in the UI
  • lastSeed: the last seed created by a deterministic type wallet. Required for unencrypted deterministic wallets, but should be empty for any other type of wallet
  • secrets: An encrypted JSON string, containing the wallet's secret data (seed, lastSeed, and private keys)
  • seed: the initial seed for a deterministic type wallet.
  • seedPassphrase: The bip39 seed passphrase. Not required, but only used for bip44 wallets.
  • tm: the creation timestamp of the wallet
  • type: Required. Can be collection, deterministic, bip44 or xpub. Refers to the way keys are managed by the wallet.
  • version: The wallet metadata version. Current version is 0.2 which added encryption support.

Wallet types

Skycoin deterministic Wallets

Skycoin deterministic wallets have the type deterministic and use Skycoin's custom [[deterministic keypair generation method]]. From an initial seed, the wallet will generate a single chain of private keys indefinitely. The seed can be any arbitrary array of bytes, but typically it is a bip39 mnemonic as bytes. The deterministic generation method does not support arbitrary indexing like bip44.

Skycoin deterministic wallets can be created and managed from the web UI.

Keypairs are saved as an array in an entries field in the wallet JSON data. A deterministic wallet with an empty or missing entries array is invalid.

A deterministic type wallet file with no entries is invalid and will not be loaded by the software.

How to manage a deterministic wallet from the cli

Note: do not perform cli operations on a wallet file while it is loaded in the Skycoin daemon or client wallet software, as this can cause data loss

# create a deterministic wallet
# the wallet will have 1 address by default; it cannot be empty
# use `walletCreate --help` for more options
go run cmd/cli/cli.go walletCreate -t deterministic -f mywallet.wlt --encrypt
# generate more addresses
go run cmd/cli/cli.go walletAddAddresses -f mywallet.wlt -n 10

BIP44 Wallets

BIP44 wallets have the type bip44 and implement the bip44 HD (hierarchical deterministic) wallet spec. From a valid BIP39 mnemonic seed and an optional "seed passphrase", two sequences of up to 4294967295 keypairs each can be generated. The first sequence is called "external" and is intended for receiving coins publicly. The second sequence is called "change"; it is internal, and is used for change addresses. When spending from a bip44 wallet, a new change address is generated for each transaction to avoid address reuse.

Skycoin does not implement the "account" feature of BIP44 wallets. The "account" node number is always 0.

Skycoin does not have a BIP44 coin_type assigned in https://github.com/satoshilabs/slips/blob/master/slip-0044.md yet, but is using 8000 while in development.

Keypairs are saved in two separate arrays in the JSON file on disk: external_entries and change_entries. However, in APIs, the two arrays are combined into a single entries array. Each element in the array has child_number, indicating the bip44 path leaf node number, and change, which can be 0 or 1, where 0 is the external chain and 1 is the change chain.

A bip44 type wallet file with no entries in its external chain is invalid and will not be loaded by the software.

How to manage a bip44 wallet from the CLI

# create a bip44 wallet
# the wallet will have 1 address by default; its external chain cannot be empty
# use `walletCreate --help` for more options
go run cmd/cli/cli.go walletCreate -t bip44 -f mywallet.wlt --encrypt
# generate more addresses
go run cmd/cli/cli.go walletAddAddresses -f mywallet.wlt -n 10

XPub Watch Wallets

XPub watch wallets have the type xpub. The wallet is configured with a single "xpub" (extended public) key. An xpub key can be exported from a bip44 wallet using the CLI command walletKeyExport.

xpub wallets can generate new addresses to receive coins or monitor balances, but cannot spend from these addresses. This enables better security for exchange and payments systems integrations, because the "hot" wallet can generate new addresses for deposits or customer payments, without exposing the private keys of that wallet on a live server.

See https://github.com/skycoin/skycoin/blob/develop/INTEGRATION.md#xpub-wallets for instructions on how to set up an xpub wallet.

Warning: Avoid sharing xpub keys. See https://en.bitcoin.it/wiki/Deterministic_wallet_tools#Risks_of_Sharing_an_Extended_Public_Key_.28xpub.29

More information about xpub keys:

Collection Wallets

Collection wallets have the type collection and are an arbitrary collection of private keys. Their type string is "collection". A collection wallet does not have a seed and thus cannot generate new private keys automatically. Private keys can only be added manually. The lack of a seed also implies that if the wallet is encrypted and the password is lost, the private keys in the collection cannot be recovered.

Keypairs are saved as an array in an entries field in the wallet JSON data. Collection wallets may have an empty entries array.

Collection wallets can't be created through the UI but can be created through the cli.

How to manage a collection wallet from the cli

Note: do not perform cli operations on a wallet file while it is loaded in the Skycoin daemon or client wallet software, as this can cause data loss

# create the empty collection wallet
# use `walletCreate --help` for more options
go run cmd/cli/cli.go walletCreate -t collection -f mycollection.wlt --encrypt
# add a private key to the wallet
go run cmd/cli/cli.go addPrivateKey -f mycollection.wlt $PRIVATE_KEY