#### Airgapped / Offline Airgapped wallets are a more pure form of cold storage that provide elevated protection against key leakage. These wallets, or wallet features, operate completely disconnected from the internet. These devices can generate a new wallet address and private key having never been connected to the internet. Private keys or transaction signatures are sometimes transmitted using methods like QR codes or physical storage media. #### Cold Storage A method involving keeping private keys isolated, largely offline, on devices not connected to the internet (e.g., air-gapped computers or hardware wallets). This approach provides maximum security but requires additional steps for signing transactions securely. Note that cold storage wallets can be connected to networked devices when sending transactions, but the goal is to avoid that where possible. See below. ### Custodial vs non-Custodial With custodial wallets, the private keys are held by a third-party entity such as a financial institution or exchange. The custodian is responsible for security measures and backup of these keys. Users access their funds through an interface provided by the custodian. Note that a user may have a custodial wallet where the custodian maintains the private keys, but the user themselves holds the mnemonic seed. In non-custodial wallets, users have full control over their private keys and therefore their crypto assets. The responsibility for securing and backing up these keys lies entirely on the user. #### Hierarchical Deterministic (HD) Wallets using a master seed value to generate an unlimited number of unique addresses deterministically. Each address can have its own private key derived from the master seed, making it easier for users to manage their funds securely across various transactions. #### Hardware Physical devices designed specifically for storing private keys securely offline while allowing users to sign transactions digitally when needed through secure elements or trusted execution environments. They provide an extra layer of protection against malware and phishing attacks. #### Paper Physical printouts or written records of a user's private key(s) and public address(es). Private keys for paper wallets are best generated offline using verified open source key generators. They offer fully offline storage, making them less susceptible to hacking or online threats. However, because paper wallets have keys printed in plain text, it is clearly a suboptimal way to keep private keys safe. Historically, paper wallets are destroyed when funds are spent/sent; that is, they were intended for single use storage and spending.