Delayed Proof of Work (dPoW)

Delayed Proof of Work (dPoW) is a consensus mechanism utilized in blockchain networks to enhance security by leveraging the hashing power of an established blockchain to protect another blockchain. It was pioneered by the Komodo platform.

In dPoW, the security of a blockchain, referred to as the "child chain", is augmented by periodically recording a summary of its state on a more secure and established blockchain, called the "parent chain". This summary is accomplished through a process called notarization.

Here's how dPoW typically works:

1. **Notarization**: Periodically, a snapshot of the child chain's state is hashed and included in the parent chain's block. This snapshot serves as proof that the child chain existed in its particular state at that time.

2. **Security Enhancement**: By notarizing the state of the child chain onto the parent chain, the child chain benefits from the higher hashing power and security of the parent chain. Any attempt to tamper with the child chain would require an attacker to overpower the hashing power of both chains.

3. **Protection Against 51% Attacks**: dPoW helps protect against 51% attacks on the child chain by requiring an attacker to not only control the majority of the child chain's hashing power but also that of the parent chain, which is often significantly larger and more secure.

4. **Examples and Cases**:
- **Komodo (KMD)**: Komodo was one of the first platforms to implement dPoW. It notarizes its chain onto the Bitcoin blockchain, thus benefiting from Bitcoin's security.
- **VerusCoin (VRSC)**: VerusCoin employs a variation of dPoW called VerusHashPoW, where notarization is done on both Bitcoin and Komodo chains.
- **Horizen (formerly ZenCash)**: Horizen utilizes dPoW to secure its blockchain, notarizing onto the Bitcoin blockchain.

dPoW has proven to be an effective method for enhancing the security of blockchain networks, especially for smaller chains that might be susceptible to 51% attacks.