rotating encryption sub keys

[Joseph Oreste Bruni]

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Would it be considered a best practice to rotate encryption subkeys on  
an annual basis, or would that be considered overkill for most uses?

I realize that messages are encrypted using ephemeral session keys  
which in turn are encrypted with public keys. Considering the small  
amount of data (i.e. sessions keys) being encrypted using public keys,  
are ciphertext attacks really even feasible?


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