Encryption where result is always readable even if key is wrong

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encryption

Hi,

I'm looking to protect some data. i.e.

Data block: ABCDEFGHIJKLMNOPQRSTUVWXYZ

I want to store a random encryption key e.t.

Encryption key: A1B2C3D4

But I want to protect this data and key from abuse by internal staff. So each user will be issued with a 4 digit code.

User code: 1234

I'm looking for an encryption technique where if the wrong key is provided it still returns a readable result, just the wrong one.

I plan to encrypt the "Encryption Key" using the user code. The user code will be provided by the user in each session.

Can anyone suggest and existing cypher or alternate technique which allow me to achieve this?

It needs to be a fairly strong encryption.