What is SD card CID number?

Internal SD card information

SD card is a device containing microcontroller and memory chip attached. SD card specific information is stored in internal registers. Each card has a set of information registers : OCR, CID, CSD, RCA, DSR and SCR. The OCR, CID, CSD and SCR registers carry the card/content specific information, while the RCA and DSR registers are configuration registers storing actual configuration parameters.

sd card architecture
SD card architecture

Today we will find out what is the SD card CID register and what information it contains.

CID register

The Card IDentification (CID) register is 16 bytes (128 bits) code which contains information that uniquely identifies the SD card. CID number is set by manufacturer and cannot be changed after is set. As a CID number is unique for each SD card, it is very often used for the software licensing and contents protection. It can be used as a random number for contents encryption, SD locking password generation or license files. However if a card does not conform to the specification or a backdoor is found this information could be changed and CID usage for security purpose compromised this way!

cid register fields
CID register fields
  • MID – 8 bit number which identifies manufacturer.
  • OID – 2-character ASCII string that identifies the card OEM and/or the card contents
  • PNM – The product name is a string, 5-character ASCII string
  • PRV – Product revision. It is composed of two Binary Coded Decimal (BCD) digits, four bits each, representing an “n.m” revision number.
  • PSN – Product serial number is 32 bits ordinary number
  • MDT – Manufacturing date, composed of 12 bits in YYM format, (offset from 2000)
  • CRC – CRC7 is a 7 bit code used for checking errors in the card register


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