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microsoft / ms-tpm-20-ref

Reference implementation of the TCG Trusted Platform Module 2.0 specification.
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the DFStart function may has two lines of code implementation that may be incorrect #103

Open magickli1 opened 1 year ago

magickli1 commented 1 year ago

Hi ，I feel that the DFStart function has two lines of code implementation that may be wrong, the following shows the code https://github.com/microsoft/ms-tpm-20-ref/blob/e9fc7b89d865536c46deb63f9c7d0121a3ded49c/TPMCmd/tpm/src/crypt/CryptRand.c#L191 https://github.com/microsoft/ms-tpm-20-ref/blob/e9fc7b89d865536c46deb63f9c7d0121a3ded49c/TPMCmd/tpm/src/crypt/CryptRand.c#L192

I think the destination parameter of the memcpy function should be dfState->buf, not dfState->iv[0], because the init variable stores inputLength and seedsize. If you copy it to dfState->iv[0], the initial value of dfState->iv[0] will be overwritten. According to the description in step 4 in section 10.3.2 in SP800-90A, the value should be stored in dfState->buf and used as the input parameter of the BCC calculation. In addition, memcpy contains 8 bytes.,so I think dfState->content should be equal to 8, not equal to 4 in the source code.is it a historical error or the current implementation is designed in this way?

In addition, part 4 of the TPM library specification implements only part of Block_Cipher_df (I think steps 10-15 are missing). I would like to ask why the complete DF function is not implemented according to section 10.3.2 (Block_Cipher_df) in SP800-90A.