Wall Street is increasingly interested in the lucrative business of crypto custody, a market that has been controversial since the early days of cryptocurrency. The principle of 'not your keys, not your coins' has long dominated the space, but major custodial banks are now looking to enter the market. However, they face regulatory hurdles such as the SEC's rule SAB 121, which establishes accounting standards for digital assets. Despite these challenges, the crypto custody market is growing at a rate of 30% per year, although it is significantly more expensive to manage than traditional assets like stocks.