php - Why have a different salt for every password? -

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this question has answer here:

adding long salt prevents attacker use rainbow table attack. add, example, fve4qrwgfagvwrvfedsgfgbvseasionvwegsf32 passwords before hashing, he's not going have rainbow table these words.

so, why use different salt every password? reason see attacker create rainbow table once default salt, , use rainbow table then. it?


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