TPM: PCR_Event VS PCR_Extend

Question

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?

Answer 1

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