Table 1.

Security feature comparison of various protocols.

Security attack	Li et al. (29)	Kumar et al. (12)	Kumar et al. (23)	Proposed
Man-in-the-middle attack	✓	✓	✓	✓
Replay attack	✓	✓	✓	✓
Patient anonymity	×	✓	✓	✓
Patient unlinkability	×	✓	✓	✓
Doctor unlinkability	×	×	✓	✓
Data non-repudiation	✓	✓	✓	✓
Data confidentiality	✓	✓	✓	✓
Message authentication	×	✓	✓	✓
Impersonation attack	×	✓	✓	✓
Stolen smart card attack	×	×	×	✓
Session key security	×	✓	✓	✓
Off-line password guessing attack	×	✓	✓	✓
Forward secrecy	×	×	×	✓

✓ - Security attack protected by the protocols.

× - Security attack not protected by the protocols.