If you have the encrypted passwords from ypcat, then they are easy to 
check.

irb(main):002:0> enc_pw = "aauZSSiXB7FbU"
=> "aauZSSiXB7FbU"
irb(main):003:0> "ruby".crypt(enc_pw) == enc_pw
=> true

irb(main):005:0> enc_pw = "$1$aaaa$jM9byC6tzuk.OYACuTQrJ/"
=> "$1$aaaa$jM9byC6tzuk.OYACuTQrJ/"
irb(main):006:0> "ruby".crypt(enc_pw) == enc_pw
=> true
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