newbie question - hashing & key rotation



I am a programmer who occasionally uses cryptography stuff.

I read this recently in a design doc - "Use SHA-1 with rotating key
for hashing data securely"

This one line stumped quite a bit (probably because of my limited knowledge
of
cryptography) & googling did not help.

I have some idea about "rotating keys" -> but this is in the context of
symmetric encryption - I think changing keys used for the encryption is
called
"key rotation". But in the context of hashing, I don't understand why
rotating
keys are. Can anyone explain?


.



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