[danuker]

> A key cutting scheme may be useful in the case of mutli tenancy

No. Cutting a key in half doesn't halve its security, but it reduces it exponentially.

256 bits = 2^256 possibilities for bruteforcing

255 bits = 2^255 possibilities for bruteforcing, or half

128 bits = 2^128 possibilities, or 1/(2^128) the security

[vageli]

You can split up a key using something like https://en.m.wikipedia.org/wiki/Shamir%27s_Secret_Sharing

[kilotaras]

1. Key is 256 bits K

2. Half of K is a random 256 bit X

3. Other half is (K xor X), still 256 bit

Having half of key is still 256 bit bruteforcing.

[AgentME]

You could instead construct a key by appending two securely-long passphrases together (which will then go through a KDF in any good encryption software). Give each passphrase half to one person. Recombining them is as simple as typing both of them into the passphrase input in the decryption software.