Which of the following is not related to security mechanism?

A security mechanism is a technique used to protect information, ensure confidentiality, integrity, authentication, and non-repudiation in communication systems.

Encryption protects data by converting it into an unreadable form.
Decryption converts encrypted data back into its original form.
Digital Signature provides authentication, integrity, and non-repudiation.

e-cash is an electronic payment method used for digital transactions and is not a security mechanism.

Therefore, the correct answer is e-cash.