There are 2 variants:

• Old MiFare-Classic variant.
• New Mifare Plus.

MiFare-classic

It's reverse-engineered. See: https://habr.com/post/141213/

MiFare-plus

It operates in security level 3 (SL3). There are no published exploits for it as fara as the author is aware. So we can't read it.

See also: Unsupportable Cards