ISO 7816-4 CLA Decoder
Decode the ISO/IEC 7816-4 CLA (class) byte: interindustry vs proprietary classification, secure-messaging bits, command-chaining indicator, and logical-channel number.
How to use this tool
What it does
Decodes an ISO 7816-4 CLA byte — logical channel, secure-messaging indication and chaining bits.
When to use it
Use it when a command's class byte carries more than the base value and you need each bit's meaning.
Worked example
Decode 0x0C to see secure messaging with a header included.
Input
Decoded
About CLA
The CLA byte sits at the start of every APDU (CLA INS P1 P2 [Lc] [data] [Le]). Its bit-fields tell the card whether the command is interindustry or proprietary, whether secure messaging is wrapping the body, whether command chaining is in progress, and which logical channel the command targets.
Spec
ISO/IEC 7816-4 §5.4.1.
Companion
Reading
Frequently asked questions
What does the CLA byte encode?
Whether the command is interindustry or proprietary, whether secure messaging applies and in which form, whether the command is chained, and which logical channel it targets.
How do I tell interindustry from proprietary?
The high nibble. 0x0X, 0x1X and similar are interindustry as defined by ISO 7816-4; 0x8X and 0xAX are proprietary, which is why vendor documentation is required to interpret them.
Which bits carry secure messaging?
Bits 3 and 4 of the interindustry CLA. They distinguish no secure messaging, proprietary secure messaging, and the standard form with or without the header being authenticated.
What is command chaining?
Bit 5 set means more command data follows in the next APDU. It is how a payload larger than a single APDU is delivered when extended length is unavailable.
Does anything I paste leave my browser?
Nothing. The tool is entirely client-side: the page ships a static script, does no network calls, and never transmits what you paste. You can confirm it by opening the network tab, or by loading the page and then going offline.