I have mine in a lock n lock and in the basement.Just found this on what I consider to be a reputable site:
Curing Salt's Curious Longevity
Curing salt has no hard expiration date. If your curing salt is only salt and sodium nitrate or sodium nitrite, it's good forever. Salt itself never goes bad, though yellowing and other discoloration is common. Moisture is a potential problem as it attracts microbes. To prevent such threats, store curing salts in dry, moisture-lock, airtight containers and in a cool dry place, such as your pantry or a dry goods storage closet. Do not refrigerate or freeze curing salt.
Yup. I just finished a container I had that was 8~9 years old.I've just finished a bag that was 7-8 years old... It's a chemical... components are bound pretty tight... I think it's good as long as it doesn't get damp... It's hygroscopic so it will suck water out of the air... keep it sealed tight... and in the dark...
It will not hurt anything if you replace it... be careful of disposal...
I purchase my pink salt (Cure #1) from Butcher Packer, usually four to five pounds at a time, which is enough for a year of curing (1 pound sealed bags). That keeps it fresh.