Crypto1 is a proprietary encryption algorithm (stream cipher) and authentication protocol created by NXP Semiconductors for its MIFARE Classic RFID contactless smart cards launched in 1994.

By 2009, cryptographic research had reverse engineered the cipher and a variety of attacks were published that effectively broke the security.

[1][2][3][4][5] NXP responded by issuing "hardened" (but still backwards compatible) cards, the MIFARE Classic EV1.

However, in 2015 a new attack rendered the cards insecure,[6][7] and NXP now recommends migrating away from MIFARE Classic.

Crypto1 consists of The usual operation of Crypto1 and Hitag2 ciphers uses nonlinear feedback only during the initialization/authentication stage, switching to operation as a LFSR with a nonlinear output filter (filter generator) for the rest of the communications.