The broad rule of thumb when encrypting is this.

Assuming your enemy knows the way the encrytion works, the data will be useless to him by the time he breaks the cypher.

That means that if your data is only sensitive for 24 hours, a basic transposition or subsitution cypher might work fine. If it is sensitive for 10 years, go for an RSA cypher, if it's sensitive for 50+ years, one time pad it.

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