A dynamically obfuscated scan chain (DOSC) includes a control module designed to control memory loading, a linear feedback shift register (LFSR), a dynamic Obfuscation Key generator configured to use LFSR to generate a φ-bit protected Obfuscation Key, in order to confuse and change the test data into an output scan vectors when the Obfuscation Key update is triggered. The DOSC also includes a shadow chain, configured to input the φ-bit protected Obfuscation Key generated by the LFSR, and output k└φ×α┘-bit protected Obfuscation Keys, and obfuscated scan chains. The DOSC operating method includes: loading control vectors to LFSR from control module during initialization; generating the Obfuscation Key at an output of the LFSR; generating the Obfuscation Key bit by bit based at least in part on the shadow chain and the Obfuscation Key during a first scan clock after reset in order to confuse test patterns.