TPM: PCR_Event VS PCR_Extend

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The TCG's "Trusted Platform Module Library Specification" states that both commands PCR_Event and PCR_Extend eventually cause an update to the indicated PCR (and its banks). In addition to that we know that a PCR can only be reset or extended. So what is the difference between the two?

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MiSimon On BEST ANSWER

For TPM2.0 i am aware of 2 differences:

Affected algorithms

  • PCR_Extend extends only the banks selected by the caller
  • PCR_Event extends all banks

Input size

  • PCR_Extend uses digests, so each value must have the correct size for the corresponding hash algorithm
  • PCR_Event can use input data between 0 and 1024 (both inclusive) octets