Terminal Network Locking via IMSI and PLMN Hash Verification

The patent applies preliminary action by pre-calculating and storing Hash values of valid PLMN numbers in the terminal before actual verification. When a SIM card is inserted, the terminal reads the PLMN number, calculates its Hash value, and compares it with the pre-stored Hash values. This preliminary preparation of Hash values enables fast and secure verification without requiring complex real-time computation during the verification process itself.

The patent replaces the simple mechanical comparison of PLMN numbers with a cryptographic Hash-based verification system. Instead of directly comparing plaintext PLMN numbers, the system transforms them into Hash values using cryptographic algorithms (MD5, SHA-1, or SHA-256). This substitution provides strong security guarantees while maintaining operational simplicity, as the Hash comparison process remains computationally efficient.

The patent replaces the vulnerable unlocking code mechanism with a cryptographic Hash-based verification system. Instead of storing and verifying plaintext unlocking codes that can be cracked, the system stores Hash values of PLMN numbers and uses cryptographic algorithms to verify SIM card authenticity. This substitution eliminates the security vulnerability of crackable unlocking codes while maintaining operational simplicity through automated Hash comparison.

The patent creates cryptographic copies (Hash values) of the original PLMN numbers and stores these copies in the terminal. These Hash copies serve as secure references for verification without exposing the original sensitive data. The system verifies SIM cards by comparing Hash copies rather than requiring users to manually input unlocking codes, thereby improving both security and ease of operation.