Function derive_private_key 

pub fn derive_private_key(
    mnemonic_phrase: &str,
    derivation_path_str: Option<&str>,
    network: Option<Network>,
    bip39_passphrase: Option<&str>,
) -> Result<String, DerivationError>

Derives a private key in WIF format from a mnemonic phrase, derivation path, network type, and optional BIP39 passphrase.

Arguments

• mnemonic_phrase - A BIP39 mnemonic phrase (space-separated words)
• derivation_path_str - Optional BIP32 derivation path (e.g., “m/84’/0’/0’/0/0”). Default is “m/84’/0’/0’/0/0”.
• network - Optional network type. Default is Network::Bitcoin.
• bip39_passphrase - Optional BIP39 passphrase. Default is an empty string.

Returns

• Result<String, DerivationError> - The private key in WIF format or an error

Errors

• DerivationError::Bip39Error - If the mnemonic is invalid
• DerivationError::Bip32Error - If key derivation fails
• DerivationError::SecpError - If secp256k1 operations fail