CMAC chips

How are they defined? §

• The NTAG424 that produces a CMAC (Cipher-based Message Authentication Code) which cost about $0.50 per chip
• CMACs are based on block ciphers like AES
  • There is a shared secret key on the chip and on the verification server that can verify authenticity of data
• Data included: UID of the chip + incrementing counter
• Similar to digital signatures, but cannot be verified against a public key
• As a result, they are somewhat “dead” — their validity can only be checked with a centralized server, if that goes down or stops getting maintained the chip is useless

Where to get them? §

I have primarily sourced CMAC chips and related software to use them from my friends at IYK! They are also cheaply available for mass purchase on sites like Amazon and Alibaba.